PDA

View Full Version : 4x5 Ultra Fine Focusing and Calibration



rvhalejr
19-Dec-2008, 22:16
For Sale:

Loupe and Stands for 4x5 Precision Plenum Photography

Focusing with GG (Ground Glass) is crude and inaccurate.

Offered here is a shimmed plenum and loupe that allows you to verify
that your emulsion plane and focal plane are aligned within .001"
by bringing both into focus simultaneously.

This allows the photographer to validate the camera system and
evaluate details that would not be possible otherwise.

Get the kind of resolution out of your equipment that would make Ansel
Adams cry. Isolate problems, calibrate and utilize equipment at the
highest possible level of performance.

With advances in sheet film scanning (the betterscanning.com fluid
scan film holder of one) you can create high quality 4x5 images that rival
several hundred dollar fluid drum scans.

Using GG is great for composition but almost useless for finely
focused precision photography. Create images reliably and consistantly
that fully exploits the 3200dpi fluid scan resolution with breathtaking
results.

To use the plenum and loupe simply remove the Ground Glass holder.
Once Focused remove the plenum, re-insert the GG and Film Holder
(or 120/220 back) and take the picture.

Satisfaction Guaranteed or Money Back (less shipping)

Pricing Includes Full Documentation and Support

DIY fabrication of the glass and shimming it to the critical dimension.

For normal to near telephoto lenses:
$79.95 for the Loupe (default center of frame stand).

For Wide Angle Angle:
$119 for Loupe and side (of 4x5 frame) stand

$149 for Loupe, side and corner (of 4x5 frame) stand

Ready to go tested shimmed plenums

$49.95 For Glass

$49.95 For Acrylic

Tools for lp/mm Lens Measurement and Profiling
$79.95 for Microscope with Reticule and CS Target.

Transactions will be conducted via ebay and paypal.
Search for "Fine Focusing Loupe" for example listings.
Let me know you saw it here so we can customize your kit.

Shipping is $10, $20 for 4x5 plenums and $30 for 8x10 plenums

Comming soon
$349 4x5 kit with everything for the serious LF photographer
$449 8x10 kit with everything + corner stand (builds on the 4x5 kit)
8x10 plenums are glass only

Still in development
$149 Precision Film Holder (+/- .0005" aligned emulsion plane), USB Black Bag Camera, Documentation and Support

$249 Precision Film Holder (+/- .0005" aligned emulsion plane), Darkroom Night Vision Documentation and Support

$Not Priced yet - Universal upgrade to CCD fluid scanning systems

IanMazursky
20-Dec-2008, 17:32
This is very interesting. I would like some more information.
Would you have any pictures or a website you can post?
I found this (http://cgi.ebay.com/Fine-Focusing-Loupe-35X-for-4x5-Film-Plane-Lens-lp-mm_W0QQitemZ230222785932QQcmdZViewItem) on ebay, is this what i would be purchasing?

Thanks

Nathan Potter
21-Dec-2008, 11:11
Ian, this is a somewhat confusing post. But yes I think what he is selling is a classic focusing telescope with a calibrated reticle within the eyepiece. The magnification factor of the telescope is so high it would require viewing an aerial image only. The second part is, I think, a film holder with a clear screen but perhaps some small fiducials on the side closest to the lens. One focuses the telescope (high power loupe) on the fiducials to capture the equivalent film plane then one focuses the LF lens at the same plane. Now both fiducial and image are exactly parfocal. Next, assuming the film holder is exactly the same design as the test holder (.191 inch depth from the holder stops; or whatever) one will have captured the exact focus plane with the film holder (minus variations in the film flatness of course, which can be significant).

Perhaps the seller can confirm my interpretation as well as yours.

Nate Potter, Austin TX.

Michael Graves
21-Dec-2008, 17:38
Either way, I think it's a violation of forum rules to point to an ebay listing or store in a FS or FT listing here.

rvhalejr
21-Dec-2008, 21:28
I'm afraid you could be right in some small sense, so someone needs to ask site admin for clarification and perhaps suggestions on how one might communicate facts gracefully without violating forum rules (and/or their intent).

We also need a judgment on if the "Critical Mission" nature of the site over rides mindless strict interpretation of its rules. In my providing carefully engineered solutions and techniques to show that film is still superior to digital (and its global marketing machine) I have hopefully served the greater good.

I was hoping to be up front as to how the for sale goods are transacted (on that big nasty auction site and its escrow mini-me who I really do not like - at all).

My guess is an using an URL is generally bad practice, but mention of a site would be ok as long as it has content with honest intellectual and LF forum value (as opposed to cross-posted spam messages we get in our email every day) and that this finding is recognized by members and moderators in general.

As another example, technically I've probably violated that URL concept (along with a
few other members) for yet another compelling LARGE FORMAT FORUM charter driven reason. We did point to a fluid film scanning product that has solved 90% of the problems with holding 4x5 film flat and Newton's rings on flat bed scanners. I've lost hundreds of hours to that problem, multiplied that by other film scanning LF members means it has likely been a HUGE problem in urgent need of a solution to many.

Furthermore I would like to scientifically prove here that film will be superior to digital for the rest of our lives given TWO things.

1.) We can scan LF film at its maximum resolution by holding it near perfectly flat
WITHOUT Newton's rings (hence the critical reference to the betterscanning.com
4x5 fluid scan holder - there you made me do it again)

2.) USING THE SAME TANGO DRUM SCAN FLUID MOUNTING TECHNIQUE (which can cost $300 for ONE full resolution 4x5 scan) to hold the unexposed film perfectly flat
(to +/- .0005") and have the emulsion plane within better that +/- .001" of the finely precision focused image (that pesky 4x5 plenum photography and loupe again - which is actually a microscope available with 90 degree, 75 degree and 65 degree stands for 4x5 wide angle lenses, one can get by with just 90 degree stand for a normal to near telephoto lens).

This far exceeds the repeatable capabilities of ground glass and as such is worthy of telegraphing this information (about the loupe with plenum kit and fluid scanning holder) to forum members, many who have already invested thousands into their equipment and never actually seen what it is really capable of doing and should
be able to do so at will and on a daily basis (another purpose of the forum I would
suppose).

So, is this forum a safe harbor for all things large format ? Or is this forum here so that the strictest interpretation on rules can trump all things Large Format ?

I guess we will find out. In the mean time I've got about a preview of about 60 pages of documentation, drawings and pictures that needs to go out to those who are
interested in more information. I know people embed URLs to pictures on the site
legally so I need to learn how to do that when time permits.

Cheers !

Richard

rvhalejr
21-Dec-2008, 22:22
Greetings Nate !


Ian, this is a somewhat confusing post. But yes I think what he is selling is a classic focusing telescope with a calibrated reticle within the eyepiece. The magnification factor of the telescope is so high it would require viewing an aerial image only.

I'm replacing the 100x microscope with components that are of much more value
the the LF work flow everyone wants.


The second part is, I think, a film holder with a clear screen but perhaps some small fiducials on the side closest to the lens. One focuses the telescope (high power loupe) on the fiducials to capture the equivalent film plane then one focuses the LF lens at the same plane.

I use a clear glass or acrylic plenum that has been shimmed to the "critical dimension"
of .190". Not only do you get mind numbing sharpness (across the entire frame) but
the film emulsion plane can be brought into sharp focus simultaneously. AN involuntary
WOW!!! comes out every time I see it.


Now both fiducial and image are exactly parfocal. Next, assuming the film holder is exactly the same design as the test holder (.191 inch depth from the holder stops; or whatever) one will have captured the exact focus plane with the film holder (minus variations in the film flatness of course, which can be significant).

EXACTLY !!! And yes, out of the box film flatness is our worst enemy. I have a solution and its status is mentioned in another post in this thread.


Perhaps the seller can confirm my interpretation as well as yours.

Not only are we on the same page, but we are both using big-o-loupes !!!

I'm not sure about the use of all the fiducials (both shims and ideally perfect
aligned planes) but after I post some pictures (will need to learn how and
see if they will let me) it should be much clearer.,.

All the best,

Richard

rvhalejr
21-Dec-2008, 22:23
> This is very interesting. I would like some more information.

Would it be ok to send the preview information to ianmazursky.com ? I don't want to be spamming anyone by accident and I'm not sure yet about forum protocol.

> Would you have any pictures or a website you can post?

I do have a pile of pictures and I'll post some as soon as I figure out how and if the
site admin will let me. I'm a old LF guy but using this site is new to me.

> I found this on ebay, is this what i would be purchasing?

Thats an old entry level listing that I should delete since there is a much better kit offered now. For the professionals I've recently decided to recommend a kit that
(1.) Provides Mind-Blowing Focus across the entire frame (got that down).
(2.) Provides a way to expose film in perfect alignment (got that down).
(3.) Hold film so flat it as a mirror like reflection with no distortion when inspecting
the holder. Currently the problem is not the holders, even though a vacuum back
cannot achieve what I want. Its the out of the box film curl that is killing us. Even
the cheap graflex holders can hold the film at +/- .001" of where we need it. I have
a solution, it uses the same taping technique as with the drum scanner. I just need
time to prototype and fabricate a one glass septum holder and test the useage of
a black bag USB camera and/or night vision IR headset in the dark room.
4.) For those of us who do not own a drum scanner, away to do a 4x5 fluid scan on
a flat bed up to 3200dpi with film perfectly flat without newton's rings, thank you
very much betterscanning.com)

So thats it. Every LF Photographer should be able to snap and digitize a 4x5 piece
film so sharp that the end product (500MB Tiff file) would make Ansel Adams cry.

rvhalejr
22-Dec-2008, 12:09
Either way, I think it's a violation of forum rules to point to an ebay listing or store in a FS or FT listing here.

I'm afraid you could be right in some small sense, so someone needs to ask site admin for clarification and perhaps suggestions on how one might communicate facts gracefully without violating forum rules (and/or their intent).

We also need a judgment on if the "Critical Mission" nature of the site over rides mindless strict interpretation of its rules. In my providing carefully engineered solutions and techniques to show that film is still superior to digital (and its global marketing machine) I have hopefully served the greater good.

I was hoping to be up front as to how the for sale goods are transacted (on that big nasty auction site and its escrow mini-me who I really do not like - at all).

My guess is an using an URL is generally bad practice, but mention of a site would be ok as long as it has content with honest intellectual and LF forum value (as opposed to cross-posted spam messages we get in our email every day) and that this finding is recognized by members and moderators in general.

As another example, technically I've probably violated that URL concept (along with a
few other members) for yet another compelling LARGE FORMAT FORUM charter driven reason. We did point to a fluid film scanning product that has solved 90% of the problems with holding 4x5 film flat and Newton's rings on flat bed scanners. I've lost hundreds of hours to that problem, multiplied that by other film scanning LF members means it has likely been a HUGE problem in urgent need of a solution to many.

Furthermore I would like to scientifically prove here that film will be superior to digital for the rest of our lives given TWO things.

1.) We can scan LF film at its maximum resolution by holding it near perfectly flat
WITHOUT Newton's rings (hence the critical reference to the betterscanning.com
4x5 fluid scan holder - there you made me do it again)

2.) USING THE SAME TANGO DRUM SCAN FLUID MOUNTING TECHNIQUE (which can cost $300 for ONE full resolution 4x5 scan) to hold the unexposed film perfectly flat
(to +/- .0005") and have the emulsion plane within better that +/- .001" of the finely precision focused image (that pesky 4x5 plenum photography and loupe again - which is actually a microscope available with 90 degree, 75 degree and 65 degree stands for 4x5 wide angle lenses, one can get by with just 90 degree stand for a normal to near telephoto lens).

This far exceeds the repeatable capabilities of ground glass and as such is worthy of telegraphing this information (about the loupe with plenum kit and fluid scanning holder) to forum members, many who have already invested thousands into their equipment and never actually seen what it is really capable of doing and should
be able to do so at will and on a daily basis (another purpose of the forum I would
suppose).

So, is this forum a safe harbor for all things large format ? Or is this forum here so that the strictest interpretation on rules can trump all things Large Format ?

I guess we will find out. In the mean time I've got about a preview of about 60 pages of documentation, drawings and pictures that needs to go out to those who are
interested in more information. I know people embed URLs to pictures on the site
legally so I need to learn how to do that when time permits.

Cheers !

Richard

rvhalejr
22-Dec-2008, 13:40
These are the first four pages of the sheet film document.

Out of the box sheet film curl is the biggest contributor to
softness. New Tools are to be tested soon so that near
perfect film flatness can be obtained prior to exposure.

rvhalejr
22-Dec-2008, 14:02
This is the Preview for the Loupe Stands on the 4x5
For a normal to near telephoto the 90 degree stand will do
For Wide Angle three stands are required for full frame coverage
90 degree for center of frame
75 degree for middle to side of frame
65 degree for corner of the frame

Note that full frame coverage for a wide angle 8x10 will use the
above stands plus one more for the corner.

Each stand has an arrow center line to be pointed at the center
of the lens aperture.

RichardRitter
22-Dec-2008, 17:19
So does the set up take into fact that sheet film is able to float around in the sheet film holder by as much as 0.010 on inch this depends on the age and make of the holder. It can also bow out more in the center depending on how the camera is being used. Also different makes of film are made on different thickness of stock varying about 0.003 of inch.

Nathan Potter
22-Dec-2008, 18:29
Whew rvhalejr! Your verbosity is really scuttling my curiosity.

Nate Potter, Austin TX.

Sizam
23-Dec-2008, 00:03
I have no idea what this thread is getting at but something tells me I want it. Is this a product usable on 8x10?

rvhalejr
23-Dec-2008, 14:27
So does the set up take into fact that sheet film is able to float around in the sheet film holder by as much as 0.010 on inch this depends on the age and make of the holder. It can also bow out more in the center depending on how the camera is being used. Also different makes of film are made on different thickness of stock varying about 0.003 of inch.

Greetings Richard,

Let me address each of the issues you have raised, but first a make a quick comment.

The kit is designed to let 90 percent of the geared 4x5 systems focus with awesome accuracy. It does, however, require skills to be acquired and a learning curve (training would be a great aid if available). You will have much better control and understanding of each lenses' characteristics than would other wise be possible.

> So does the set up take into fact that sheet film is able to float around in the
> sheet film holder by as much as 0.010 on inch this depends on the age and
> make of the holder.

As you have indicated, getting this finely focused precision image onto film is the biggest problem right now. The higher end kits are designed to help weed out the
poor holders from the better ones. As far as .010 of an inch goes Quick Loads and Ready loads (and out of flat holders in general) are so sloppy that better focusing will have almost no effect and are not recommend unless a lot of softness is acceptable.

> It can also bow out more in the center depending on how the camera is being used.

Yes, that is a known problem with some types of photography, 8x10 and larger formats.

Yet it is possible to tape down film (using a refined version of the betterscanning.com method) to better that +/- .001" (it will have a perfect mirror reflection with no distortion). To my knowledge, there is not a holder available yet to hold this type of septum (or precision plenum). :( sigh

Right now out of the 4x5 box film curl is killing us. If you are lucky enough to get 4x5 fuji, kodak, ilford, etc. out of the box flat (ideally within +/- .0005") and place it in a good quality film holder (flat within +/- .001") one can capture an outstanding image.

> Also different makes of film are made on different thickness of stock varying about 0.003 of inch.

Absolutely. Off the top of my head I think 4x5 films vary from about .006" to .010"
these days. 120/220 backs seem to work well (that reverse curl is known to cause problems if the film sits to long though) and is generally thinner than the sheet film.

The critical dimension will vary (as the documentation discusses) from film type to
film type. That means a dedicated precision plenum will be required for each type
of film and a validating set of bracket shots (with an incrementally differing critical
dimension for each) will be required for every system otherwise we are back to
guessing.

All the best,

Richard V. Hale Jr. (hence the unique rvhalejr user name)

rvhalejr
23-Dec-2008, 14:31
Whew rvhalejr! Your verbosity is really scuttling my curiosity.

Nate Potter, Austin TX.

Its an important technique used to avoid mis-understanding, which we have all
had to much of already.

rvhalejr
23-Dec-2008, 14:35
I have no idea what this thread is getting at but something tells me I want it. Is this a product usable on 8x10?

Yes, I have an 8x10 plenum in stock and 3 out of 4 the four loupe stands ready to go.

rvhalejr
23-Dec-2008, 14:46
There are about 8 .pdf pages attached to messages above that
contain information and images that describe the product in
more detail.

Kirk Gittings
23-Dec-2008, 15:42
I have moved this to the "announcements" area as this is a product that may interest many. The "for sale" area is NOT for business to sell their wares and clearly states that. This thread should be kept to providing information about the product and related questions. Sales should be handled through the business' web site. Links to Ebay sales et all are not acceptable.

rvhalejr
24-Dec-2008, 13:47
I have moved this to the "announcements" area as this is a product that may interest many. The "for sale" area is NOT for business to sell their wares and clearly states that. This thread should be kept to providing information about the product and related questions. Sales should be handled through the business' web site. Links to Ebay sales et all are not acceptable.

Attached are 4 preview pages (1,2,3 and 17 with images) of the loupe stands.

Policy Noted, Thanks,

Richard

rvhalejr
24-Dec-2008, 14:28
I have moved this to the "announcements" area as this is a product that may interest many. The "for sale" area is NOT for business to sell their wares and clearly states that. This thread should be kept to providing information about the product and related questions. Sales should be handled through the business' web site. Links to Ebay sales et all are not acceptable.

Attached are four Sheet film preview pages (1,2,3,4 images and documentation)

Policy Noted. Some of the challenges posed by out of the box film curl are
mentioned here.

If you are lucky enough to be using perfectly flat film in a good quality holder
then the following does not apply. However, if the film you need to obtain
a specific look (a unique brand of C41, E6 or B&W) is curled out of the box
then the following may be of interest.

The fourth page is the most significant as it contains the reflection from
the emulsion of a 4x5 film that has been taped down to +/- .0005" using
rollers similar to drum scan mounting or that documented with the flat
bed betterscanning 4x5 film holder.

This reflection was carefully inspected for any distortion and was verified to
be mirror like. This demonstrates that out of the box film curl can be tamed.
The bad news is that the septum size in the 4x5 film holders is to small to roll
and tape mount film (it was a very time consuming experience and was very
disappointing when it failed on the very last step).

An Infrared camera and or Headset have not been tested yet for use in the
black bag or dark room.

Crafting a "film holder" to expose plenum rolled and taped film is proving to be
(as expected) extremely difficult, expensive and time consuming. Hopefully a
working prototype will eventually result in something I can use reliably without
that much difficulty.

All the Best for Now,

Richard

Sizam
26-Dec-2008, 14:13
I'm still intrigued but I'm not getting exactly what your selling and how to use it. The PDFs read like a biochemistry article on the subject of focusing and film flatness, I need to see an instruction manual and an actual 1-2-3-4 step process of what it is I'd be using and how I'd use it.

Is there a glass sheet that I tape my 8x10 film onto that I slide into some sort of special film holder you provide?

Nathan Potter
26-Dec-2008, 17:35
The most logical solution to in camera film flatness would probably be a vacuum holder. But certainly not so easy to implement technically. There are small portable low vacuum devices used for picking up small parts and something like that could be adapted for the purposes of holding film flat. One would need to design a special film holder of course but I'm sure that could be accomplished. Probably not useful for Quickloads though.

But given the myriad of variables that degrade image quality under practical field conditions I would question the utility of being really fanatical about film flatness in the field. Sounds more like an exercise necessary for precision scientific photography.

In fact I used the vacuum hold down approach for the photo documentation of IC chips before features became so small as to not be resolvable with standard lenses. The film plate was specially machined with a few hundred tiny holes accessing the vacuum space under the faceplate. The vacuum space was connected to a small hose which was attached to a dry vane pump capable a few tens of mTorr vacuum. I sort of wish I had my design for the device now.

Nate Potter, Austin TX.

rvhalejr
28-Dec-2008, 13:52
But given the myriad of variables that degrade image quality under practical field conditions I would question the utility of being really fanatical about film flatness in the field. Sounds more like an exercise necessary for precision scientific photography.
Nate Potter, Austin TX.

A working vacation for photographers can put them on a location where a once in a
lifetime money shot can be taken.

The holy grail of 4x5 photography is a 16bit fluid scan that yields >= 400 mega pixels of an image worthy of high acclaim. The end-product is mural fine art (see my profile for amusement and muse).


In fact I used the vacuum hold down approach for the photo documentation of IC chips before features became so small as to not be resolvable with standard lenses. The film plate was specially machined with a few hundred tiny holes accessing the vacuum space under the faceplate. The vacuum space was connected to a small hose which was attached to a dry vane pump capable a few tens of mTorr vacuum. I sort of wish I had my design for the device now.

In another life I also used high vacuum equipment. I've done a prototype and the
problem encountered was that the film gets rumpled at each hole (with a hole density of about 100 and hole size of about 1/16" ... I have not tried smaller hole sizes (I do have a micro-bit set now) and higher hole densities (200 or 400 - ugh).

Rolling and taping (for film scanning) does hold film perfectly flat. But designing a
a precision holder to accept the plenum/septum is extremely problematic, expensive and time consuming.

In the end it may be less work using a well calibrated pan head with the mural being
a sequence of panels that look like windows. The experience viewing a sectional
verses a continuous display would be different. Perhaps one might be better than the other in different environments.

rvhalejr
28-Dec-2008, 15:08
I'm still intrigued but I'm not getting exactly what your selling and how to use it. The PDFs read like a biochemistry article on the subject of focusing and film flatness, I need to see an instruction manual and an actual 1-2-3-4 step process of what it is I'd be using and how I'd use it.


For sale are
(1) the tools and instructions for taking pictures worthy of a tango (or betterscanning.com flatbed) fluid scan (maybe as high as a giga pixel for 8x10)
(2) the tools and instructions to characterize your lenses (and entire system end-to-end) using the lp/mm MTF metric

There are some many derivative functions and improved capabilities that it is improbable that I could ever describe them all in a way that would satisfy everyone's questions.

Lets just summarize it by saying that the tools and documentation are very powerful
both optically and functionally.


I need to see an instruction manual and an actual 1-2-3-4 step process of what it is I'd be using and how I'd use it.


The 1-2-3-4 alignment instruction document is in the works. Its purpose is for bringing the emulsion plane into perfect alignment with the lens image plane. This is done with feeler gauges, glass gauge blocks, stainless steel rule and honed digital calipers with the .0005" touch feature.

The first task is to characterize the film holders for the critical
dimension (back of camera mating surface to emulsion plane). Once critical dimension
is known a set of bracket shots is taken with plenums shimmed in .001" increments
in and on either side of the emulsion/image plane.

The focus of each shot is done with a piece of developed film you plan to use (taped
to the plenum glass in the flat emulsion/image plane at the critical dimension distance from the back of the camer), a 35x loupe and the 90, 75, 65, and 55 degree stands to cover the entire (160mm 8x10 wide angle) frame. You do not need as many stand changes for normal and near telephoto lenses.

How you bring the center, middle, side and corner of the image into fine focus is
dependent on your lens lp/mm profile characteristics, scene and your style.

The scene image will be in focus at the same time and distance as the grain in the developed films emulsion layer. These planes are aligned to one another (residing in the
same space as close as possible) and calibrated for use with a specific film thickness
and set of holders.

Once you determine which plenum shim distance works best you will shoot with that
from that point forward UNLESS the thickness of your film changes or you use a different type of film (that has a different thickness).

This instruction is a lot different from that of characterizing lens MTF lp/mm measurements (as was described in the older auction site ads).


Is there a glass sheet that I tape my 8x10 film onto that I slide into some sort of special film holder you provide?

If your film does not curl out of the box then a standard film holder should work fine.
8x10 film does seem to have a problem with sagging because of its size and weight.

Rolling and Taping the film to a glass septum will hold the film down with mirror like
precision.

I'd love to provide such a beast (and would be very happy if anyone else did for that
matter).

The 8x10 is going to wait until the 4x5 version is complete.

The biggest issue with rolling and taping is that the glass-septum needs to be about the same size as the film holder to give the tape something to hold onto. This makes
it very difficult to design a film holder that provides plenty of tape room and enclose
the septum and dark side(s).

Precision pieces of sheet metal held together by machine screws (in a laminar fashion) seems to make the most sense at this point.

All this pain is a result of the film OEMs not making film that does not curl. If the fine
focusing methodology becomes generally accepted I would love nothing more than to
see flat film come fresh out of the pouch (box).

bglick
29-Dec-2008, 19:46
I am with Nathan on this one....

But first, i would like to applaud the OP for his tenacity in his pursuit, we need more people like this in LF :-)

Like others, I am a bit confused....but I think I finally understand the targeted goals of the products presented:

1) A method to check / correct the film plane vs. the focus plane (in our case, the gg)

2) A method to make film flat while used in a film holder, to prevent focus errors where film curl, or film buckling exist.

3) A method to place keep film flat while being scanned, and the film resides exactly on the focus plane.

Am I missing anything?

Based on this, here is a few thoughts on each of the above...

1) With most modern cameras, probably mid 80's +, makers go through extremes to keep the film plane and focus plane aligned. This is true of the better film holders as well. Often this task is confirmed and / or tweaked with lasers, which offer precision well beyond what the eye can accomplish via optics. More vintage cameras / film holders would probably benefit from the OP's system.

Keep in mind here..... if the film plane and focal plane are out of alignment, we are often saved by high f stop numbers LF uses. If LF lenses were shot at f4.0, I too would be chasing flatness down to .001".... but in non-macro photography, this issue is not so critical, such as landscapes.

Example, at f22, using .017mm for cc value (60 lp/mm), the film can vary from the focal plane by as much as +/- .015" and still acheive the desired on film resolution. This is 15x greater than .001". At f45 this "depth of focus" slop variable doubles, at f11 it's cut in half.

Also, assuming you are not photographing a flat subject (which would be a good application for the OP product), mis alignment between the film plane and focal plane greater than the amounts above, doesn't reduce resolution on the film, it simply changes the focus distance on the other side of the lens (the scene). For example, lets assume a 150mm fl lens, and you set focus at 40ft. If the film is sitting .015" further back, it will produce sharp focus at a 34ft distance. In most cases, this will rarely have any negative effects on the image recorded.... which is the beauty of LF, it really does have inherent built-in allowances for errors. Our errors of focusing are greater than this, i.e. if you tried several attempts to focus at 40ft on a ground glass, the true fl distance would vary between 35 - 45 ft... the reason is, the gg is not of sufficient resolution to enable better focus. Then toss in movement of the lens panel when locking down focus, inserting film holders, etc. Errors are everywhere.... film / gg alignment is certainly not the "weak" link in the chain. There is many weak links.


In addition, these errors are more likely to exist with lens and film standards not being square to each other, specially in older wooden vintage cameras....as wood moves over time. I would focus on these issues first.

Also a high precisioned straight edge, by a company such as starrett, combined with a high precisioned dial indicator with a roller wheel tip, at .0001" resolution, is a much simpler method IMO to pick up any errors between film plane and gg alignment. You can buy flat sheet shims in thicknesses from .001" to .1" in any increment you want, to simulate the film thickness. You can cut these shims to the film thickness you use, to make a perfect calibration between film holder and film of your choice. The shims at MSC are dirt cheap, less than $15 for a pack of multiple thicknesses. To get really picky, you need to have the focal plane lay in the middle of the grain thickness, which excludes the film base. Of course, films are close enough in thickness where this really is not a problem, unless you have a very unique application....maybe gigabyte film shot at f5.6?


2) The same numbers above, apply to film curl, or lack of film flatness. I see this being problem in two areas.... the first is, pointing the camera downward, specially with 8x10 film, the center will buckle. And secondly, roll film sitting too long in a reverse curl film holder, which there is no good solution for, other than wasting that next exposure. As for holding film flat in film holders, as mentioned previously, micro holes with a small hand pump will make the film perfectly flat, even roll film. I have this with a 6x7 RFH, and it works superb... I have not felt compelled to do this with sheet film. There has been a few makers of vacuum back film holders.... Schneider made them in 4x5 and I think Hoffman made them in 4x5 - 810.


3) Scanner film flatness. This is can be a useful tool if the scanners focal point is not on the film plane. On a flat bed scanner, I lay AN glass over my film, with Kami fluid, and all film is perfectly flat. With the consumer based scanners, this might be an issue, as I am sure QC is limited. Not sure if the betterscanning.com solution can get the film below the glass plane.

Most scanners use lenses in the f5.6 region...this again leaves sufficient Depth of Focus at the film plane, where changes of focus distances of .001" will not deliver any sharper results. The quality of the lens, the quality of the recording device, the quality of the light and electronics is what delivers a great scan. However, I am not discounting the value of confirming the lens focal plane is well aligned with film plane. I think Doug did a great job of exposing this shortcoming...

bglick
29-Dec-2008, 22:14
Following up on the scanner calibration I mentioned above...

On Better Scanning web site, they show the improvement in a .07" focal plane alignment correction, 70x greater than the mentioned .001" correction, and even then, it's not extreme, but still worth it IMO...

http://www.betterscanning.com/scanning/vb_advantage.html

rvhalejr
30-Dec-2008, 00:33
Thanks for the detailed post outlining concerns. Its a long one so it will take some
time to cover all the points raised. If you don't mind me asking I noticed the bglick
post of 16-Aug-2005 "cc vs. lp/mm as it relates to hyperfocal distance"

If that is not a good place for me to gather background information on your perspective feel free to let me know.


I am with Nathan on this one....
...but I think I finally understand the targeted goals of the products presented:
1) A method to check / correct the film plane vs. the focus plane (in our case, the gg)
2) A method to make film flat while used in a film holder, to prevent focus errors where film curl, or film buckling exist.
3) A method to place keep film flat while being scanned, and the film resides exactly on the focus plane.
Am I missing anything?

No.


Example, at f22, using .017mm for cc value (60 lp/mm), the film can vary from the focal plane by as much as +/- .015" and still achieve the desired on film resolution.
No.

Let me assert that "the desired on film resolution" are the same results
that Ansel Adams got at Yosemite, with the end results being a nearly ideal
400 megapixel+ image (resulting from perfectly exposed 4x5 fluid scanned film).

Also I tend to verify, test and document everything, over, and over and over .,.

This is not the first time I've heard that the focal plane envelope of optimal
focus can vary "as much as +/- .015" especially by those who use quick loads
and ready loads. I do not recommended using them because they are known to be very soft.

I thought it was obvious to most that by looking at an unexposed piece of film
in one of those "its so easy" quick and ready things in broad daylight that the
emulsion layer's reflection and distortion at the edges reminds one of a circus
mirror and the scanned results cannot be anything but laughable.

Maybe thats one complication, you are not differentiating between focal
plane flatness, incrementally moving the plane up to a distance of +/- .015
(along the normal vector) AND nasty film curl which is helical in nature,
remembers the curve of the roll it came off of and is a good example of distortion.

I can make since of the former and see that there may exist a lens lp/mm profile
(center, middle, edge and corner of frame circumscribed by the behind lens
conic section) that at a small aperture (approaching the Rayleigh limit) or
pinhole resolve an image within an envelope approaching +/- .007 .,.

Time to put on the Test Engineering hat and figure out what is going on with
this assertion these learned scientists have made.

This perhaps (though unlikely) with the condition that the center, middle,
edge and corner of frame lp/mm values are IMMUTABLE throughout that
envelope !!! (You can-not have good focus if its constantly changing as
a function of the lenses full profile).

OOOOOOOHHHHHHH !!! AAAAAHHHHHH !!! If the pinhole (tiny itsy bitsy aperture)
assertion about the envelope is true, maybe there is some use for
the Nyquist 3d 2*root(3) here, but alias, I regress (sorry,
getting back on target). For the record my working range is usually f8
through f22, ok add an fstop to eather side for less than ideal conditions.

I apologize to the f64 and up folk, I've spent way to much time in another
life modeling knife edge photon scatter in hundreds (maybe thousands) of
photo micro graphs (and 3d beam topologies, 10, 50 and 90 percent
energy lines, etc.).

Ideally this experiment will have four scopes locked on USAF targets and
instrumenting lp/mm as we rack through the normal base envelope AND
that these supposed IMMUTABLE values are recorded on film (as observed)
and easily studied in the fluid scanned generated image (our real world
work flow).

Other constraints (not mentioned, for example, could be) excellent signal
to noise ratio and perfect point resolution, modeled as slope at a point,
correlation with knife edge photon scatter, standard deviation and
(but not limited to) other generally recognised scientific and engineering
methodologies.

Well, even if I fall flat on my face its always best to tell everyone exactly
what I'm going to do, listen to any an all suggestions and complaints,
and then execute it. Let the facts be what they may.

The resolving power of a wide angle schneider lens focused on a power line
(and insulators that hold it) at 100 yards @ f22 is impressive, but seem to be
resolved at one and only one point on the rack an pinion focusing mechanism
(and NEVER behind ground glass - yes I'm a Beattie Ultra-bright addict but only
for composition of the frame as a whole).

I've got a chart somewhere about how ground glass does bad things to sharpness
so if all of your testing has been done behind GG with ReadyLoads I'd need three or
four stiff drinks before telling you the were in focus (my wife calls be a film snob
so I apologize to those who are happy with Quickloads and GG - happiness is
a good thing).

I've tested, verified and documented this over and over again and will
continue to do so. I'd love for your assertion to be true because if I could
re-create it 4x5 photography would be much simpler but alias, I am never
that lucky (sigh).,.

I'm happy for you that there are many a math model that proves this, but
I want to see the results come out of a Heidelberg Tango or Higher end
CCD scanner. Then (what ever the results) look at and maybe come up
with a little math model or two.

Now on the off chance that your assertion is correct I hope to be running
yet another test soon !!! But this time it will be with a piece of mirror
like mounted film inside a newly fabricated film holder.

Now I've really done it, let the cat out of the bag, I hope i do not get
eaten.

I'll use three different shnieider lenses (all wide angle - hopefully one will
have this magical focal plane property under normal use). I do not plan to
go above f32 but should probably use it for completeness. I'm apprehensive
about f64 because it is so dark and there are diffraction issues.

Then I'll run the film through some calibrated wooden graphic holders,
some calibrated plastic elites and then those quick ready easy load things
(choke - anything for science).

I hope I can find a lens that will give me +/- .015 inches of sloop to play with,
but I characterize those things to death although usually not at
infinity. If I cannot reproduce your assertion I'll even go as far as testing
lp/mm with big USAF targets at infinity with a wide angle, normal
and near telephoto lenses (on a foot ball field - anything for science).

Its always fun to learn something new. If there is any way to re-create the
effect described above I will quantify, qualify, study and test it to death.

But I need to actually fabricate that super flat film holder just to be on the
safe side.

All the best,

Richard

rvhalejr
30-Dec-2008, 08:36
Please supply the following information

I. A lens characterization profile (lp/mm matrix) with
A.) Center, Middle, Side and Corner of lens (x axis)
B.) f16, f22, f32, f64 (the limit of pinhole size is your choice along y axis)

II. Repeat with film (or sensor) plane offsets (along the normal
vector) of .007" , .015" , .021" (more if desired).

III. State distance to target, mm size of wide angle lens and
format (6x9, 4x5, 8x10, etc).


Use of common window glass (shimmed for offsets) is fine.
A 35x better pocket microscope is required for somewhat accurate measurements.
For 4x5 90, 75 and 65 degree angled microscope stands are needed.
For 8x10 a 55 degree angled microscope stand will be needed as well.


Best Regards,

Richard

bglick
30-Dec-2008, 12:06
Hi Rich

Thank you for the thorough response....

The only reason I mentioned cc, was how it related to focus plane alignment, NOT hyperfocal distance, which is a completely different issue, un related to the discussion here.


> 400 megapixel+ image (resulting from perfectly exposed 4x5 fluid scanned film).


Rich, through the years, the web is flooded with mis information about how much data film can hold vs. digital recording media. Here is the short version of what is possible with 4x5 film. First, we leave out the scanner, lets ASSUME it will grab every bit of resolution from the film, (regardless of the oversampling required) so that variable is removed. Now it comes down to lens aerial resolution at the f stop used and the MTF of the film. First, use color 4x5, f32. Assume the lens is diffraction limited at f32 (it never is, but lets give film its best chance)... 1500/32 = 47 lp/mm aerial resolution. Lets use the MTF for the color film at 65 lp/m.... a good avg. Combine in the time tested 1/R equation,

1/R = 1/(1/r1 + 1/r2)

R = System Resolution
r1 = Lens aerial resolution in lp/mm
r2 = Film MTF in lp/mm


The On Film Resolution (OFR) is 27 lp/mm. If you extract this out over a 90x120 mm film area (4x5), it will equal 32MP of resolution....this is nothing new, it has been tested by every major lens and film maker for years. There has been many tests that bring 4x5 color film very close to 39MP digital backs. Based on the f stop used for each, the scales can tilt in either direction.... as an example, if you shoot at f11 instead of f32, the OFR jumps to 84MP, a huge increase and will outperform the 39MP digital back, assuming the subject matter can withstand such small DOF range.

If you substitute B&W film, say TMax at 120 lp/mm vs. color, at f32 this value jumps to 49MP, and at f11 176 MP. Still no where near the 400MP you quote, and these are BEST CASE scenarios with a perfect camera system and diffraction limited optics, perfect alignment, etc. And as you know, at f11, the DOF is so small, you will be forced to shooting subjects that are flat, or at infinity. It seems all the digital vs. film comparisons I see, fail to make these associations.... the variables are so great, the resultant outcomes are "all over the map". That is the nature of optics, all variables must be considered in a comparison, and often the photo community wants short n sweet answers to everything. But anyway, hopefully this will bring some realistic MP values into play.


> This is not the first time I've heard that the focal plane envelope of optimal
focus can vary "as much as +/- .015"


This is based on ONE single f stop.... the depth of focus principle of the film plane has been an accepted optical principle for over 100+ years. As you know, Depth of focus is a function of f stop only, not fl. As f stop increases, so does Depth of Focus, hence the amazing viability of LF photography...


As for film curl in sheet film... I personally have never seen it in the thousands of sheets I have used... and when I insert film into my film holders, the edges are held very secure, forcing flatness, spcially in 4x5 which is small enough to prevent bulges, unless you point the camera downward. I have shot quickloads for years, and never had a problem with what you describe, maybe I got lucky batches.... Fuji understands this problem very well... But to be clear, I never shoot LF at f8 either, where any of the problems you mention could surface. So the application is significant factor here ....


> Time to put on the Test Engineering hat and figure out what is going on with
this assertion these learned scientists have made.


Grab any books on photo optics and read about Depth of Focus.... its a simple optics equation that makes perfect sense. Think of it as Depth of Field at the film plane. But more importantly, if you are shooting a scene with depth, the mis alignment issues do bring different parts of the scene into more/less focus...and with a lot of depth, its impossible to evaluate this after the exposure....unless the error was soooo great it might be obvious. The only example I can think of, is extreme curl in roll film, from sitting on a reverse curl, 180 deg roller too long.



> This perhaps (though unlikely) with the condition that the center, middle,
edge and corner of frame lp/mm values are IMMUTABLE throughout that
envelope !!! (You can-not have good focus if its constantly changing as
a function of the lenses full profile).


the examples above, assume consistent aerial resolution on the entire film circle radius. At high f numbers, such as LF...this is decent assumption...as stopping down tends to level the playing field.... but the center of any spherical optic will always be sharpest. So you can reduce the numbers I provided above by 20% to be safe....again, in most cases, we are trying to get in the ballpark.... If you look at Schneiders Website, you can get the MTF curves of all the lenses made, and see radius performance levels out at high f stops. But certainly not true at f5.6, which LF lenses are never optimized for, except the new digital lenses, which can be used for RF or digital backs.


> For the record my working range is usually f8 through f22,


LF lenses will perform very poorly at f8.... these lower f stops are used to produce enough light on the ground glass to compose the image - otherwise, they would not be offered on the lens, they are not for exposing. Most all 4x5 and 810 lenses are optimized in a tight 2 f stop range..... shorter fl's in the f16-22 range, and the mid fl lenses, in the f22-32 range, and the longer fl's in the f45 range. The abberations at f8 on 98% of LF lenses are so degrading, you often can produce a better image at f64. There is a few rare exceptions, and these are very new SSXL designs and a few others, whereas in the short fl's they can be used at f11. But regardless, at f8 - f11, you are reduced to shooting flat subjects or infinity to hold resolution..


You seem to be in agreement with focus error being a necessary evil of LF in general. And of course, the big issue not mentioned is, when you focus at f5.6 and then stop down to f45 to shoot, you have shifted the focus plane, another weak link in the chain here, specially when considering the alignment precision you are pursuing. In other words, no matter how perfect the alignment is in all aspects of the camera, the shortcoming will be the inability to focus precisely, and the inability to focus well enough at higher f stops, due to lack of light. Of course, this is not justification for the rest of the camera system to be completely out of alignment.... but it demonstrates why ultra precision film/gg alignment will often not improve the final OFR.


> If I cannot reproduce your assertion I'll even go as far as testing
lp/mm with big USAF targets at infinity with a wide angle, normal
and near telephoto lenses (on a foot ball field - anything for science).


I have tested all types of lenses for many years.... and its truly remarkable when the set-up is right, how it confirms the math and often the MTF values the makers provide. This is for both film and digital. keep in mind, a football field is extreme. You don't need targets this far from the lens. Chris Perez has done an excellent job testing lenses of all types, I am sure you have seen his web site? His results concur with everything I have ever tested.

http://www.hevanet.com/cperez/testing.html

Thank you again Chris for being such a big supporter of the LF community.

To be clear Richard, I am not knocking your desire to achieve the flatness you desire. And in some extreme shooting situations, I am sure it will be very helpful, such as f5.6 - f8 doing reproduction work of 2d subjects. But using common LF lenses, which probably 90% of them in existence, are designed to be shot at f22 - 45, their is such a large inherent slop factor, in the end...the means don't justify the ends. If you follow this forum, you will see this issue surface every few years.


I think a more obvious area of attack to improve image quality is the squareness between the front and back standards, specially with short fl lenses shot at f8 - f16. As slight un-squareness presents huge variances in the focal plane vs. the film plane. Of course, this problem is magnified in 810 vs. 45.


Comments on your 2nd post....

A good test, to reduce testing time, is to first test the lens with a digital back. I have a set-up that enables a DSLR to mount as a film holder. This gives you a "sure" flat recording plane, and a great focus mechanism, as I use after-market focusing screens sold by Katz Eye Optics - with these screens you can really nail the focus to the levels of accuracy you desire. Now you have a basis to compare film with... Digital recording is subjected to the same 1/R curse....(which is Nyquist theory in action) of course, SWA and even some WA lenses will not perform well with most digital sensors, as this still a weak link in digital sensors....


Anyway, we all are interested in your findings.....

Peter De Smidt
30-Dec-2008, 13:05
Not that long ago, I exchanged info on line with a guy who made a DIY 4x5 vacuum holder. It didn't look that hard to do. It turns out that a rubber bulb pipette bulb has enough suction. I no longer have the contact info, but a little Googling should turn it up.

rvhalejr
30-Dec-2008, 22:55
We are running out of space so I've had to leave some of the good stuff
behind (sigh) :(


Hi Rich
> 400 megapixel+ image (resulting from perfectly exposed 4x5 fluid scanned film).

Lets use the MTF for the color film at 65 lp/m.... a good avg. Combine in the time tested 1/R equation,

1/R = 1/(1/r1 + 1/r2)

R = System Resolution
r1 = Lens aerial resolution in lp/mm
r2 = Film MTF in lp/mm

The On Film Resolution (OFR) is 27 lp/mm. If you extract this out over a 90x120 mm film area (4x5), it will equal 32MP of resolution....this is nothing new, it has been tested by every major lens and film maker for years. There has been many tests that bring 4x5 color film very close to 39MP digital backs. Based on the f stop used for each, the scales can tilt in either direction.... as an example, if you shoot at f11 instead of f32, the OFR jumps to 84MP, a huge increase and will outperform the 39MP digital back, assuming the subject matter can withstand such small DOF range.

If you substitute B&W film, say TMax at 120 lp/mm vs. color, at f32 this value jumps to 49MP, and at f11 176 MP. Still no where near the 400MP you quote, and these are BEST CASE scenarios with a perfect camera system and diffraction limited optics, perfect alignment, etc. And as you know, at f11, the DOF is so small, you will be forced to shooting subjects that are flat, or at infinity. It seems all the digital vs. film comparisons I see, fail to make these associations.... the variables are so great, the resultant outcomes are "all over the map". That is the nature of optics, all variables must be considered in a comparison, and often the photo community wants short n sweet answers to everything. But anyway, hopefully this will bring some realistic MP values into play.


3200ppi is the recognized maximum for high end photography (I've seen it from those way more accomplished than I).

3200ppi^2 == 10 Megapixels per inch of film

4x5 == 20 inches (its not really 4x5)

20 X 10 Megapixels == 200 Megapixels (full color RGB ones, 16bit color depth)

The 39MP digital backs are actually Monochromatic photo sites, 1 pixel is
ether Red, Blue or one of two Greens.

So we can call the 39MP what is is a full color 10MP camera with a bit level depth of 12 (in true kodak fashion you really have to dig to find that one).

Using Monochromatic Digital Back accounting the film 200 RGB Megapixel is actually
600 Mega Monochromatic (less 25% for lack of two greens) is 450 Mega pixels based on monochromatic rgbg photo sites. But 400 seems close enough to make the point.

However, Bob, for general public consumption I defer to your wisdom and stand corrected.



> This is not the first time I've heard that the focal plane envelope of optimal
focus can vary "as much as +/- .015"

This is based on ONE single f stop.... the depth of focus principle of the film plane has been an accepted optical principle for over 100+ years. As you know, Depth of focus is a function of f stop only, not fl. As f stop increases, so does Depth of Focus, hence the amazing viability of LF photography...

Admittedly Scheimpflug is out of scope for me. f8-f16 is good for the 35mm or DSLR spotmeter, f11-f22 for 120/220 backs on 4x5, and f32 is good on a sunny day but freezing movment becomes problematic for me.

I only find use for a limited number of movements and as you probably know use the
4x5 more like a press camera than what is described in bobwheeler.com/photo/ViewCam.pdf



As for film curl in sheet film... I personally have never seen it in the thousands of sheets I have used...

I need to buy my film from you and/or other kind souls on the forum who are
well connected. Having flat film out of the box makes things much easier.

Still, I'd like you to shoot the mirror reflection of your unexposed flat film in a
holder and post it here (like i did with the roll and tape mount example). Carefully
inspect for any distortion or departure from what should be a mirror like image.

Trust but verify.



> Time to put on the Test Engineering hat and figure out what is going on with
this assertion these learned scientists have made.
Grab any books on photo optics and read about Depth of Focus.... its a simple optics equation that makes perfect sense. Think of it as Depth of Field at the film plane.


Depth of Focus has some value (probably much more to view camera purists), but I have to to resist relying on it as an excuse to not shim the plenum so as to
bring Image Focus into the Emulsion Plane.

I glady leave the exploitation of Depth of Focus (and the lack of any need to
shim their plenums, or calibrated their film holders) to View Camera True Believers.


> For the record my working range is usually f8 through f22,



LF lenses will perform very poorly at f8.... these lower f stops are used to produce enough light on the ground glass to compose the image - otherwise, they would not be offered on the lens, they are not for exposing. Most all 4x5 and 810 lenses are optimized in a tight 2 f stop range..... shorter fl's in the f16-22 range, and the mid fl lenses, in the f22-32 range, and the longer fl's in the f45 range. The abberations at f8 on 98% of LF lenses are so degrading, you often can produce a better image at f64. There is a few rare exceptions, and these are very new SSXL designs and a few others, whereas in the short fl's they can be used at f11. But regardless, at f8 - f11, you are reduced to shooting flat subjects or infinity to hold resolution..


I love shooting f32 or f45 if there is enough light and lp/mm is still very good for
that lens. However, if I want to pull detail out of shadows (for HDR) f8 can look
pretty good as the low end of a Bracket Sequence (f8, f16, f32)



You seem to be
in agreement with focus error being a necessary evil of LF in general. And of course, the big issue not mentioned is, when you focus at f5.6 and then stop down to f45 to shoot, you have shifted the focus plane, another weak link in the chain here, specially when considering the alignment precision you are pursuing. In other words, no matter how perfect the alignment is in all aspects of the camera, the shortcoming will be the inability to focus precisely, and the inability to focus well enough at higher f stops, due to lack of light. Of course, this is not justification for the rest of the camera system to be completely out of alignment.... but it demonstrates why ultra precision film/gg alignment will often not improve the final OFR.


No. In the hands of someone like yourself the fine focusing kit will allow you to
reach heights you never thought possible. Use it a few times and you will not
want to part with it.

I think .001" (as a goal) is just good precision (thats why my fan club is in Germany) leaving the other .014" to be used by the view camera photographer as they see
fit.



I have tested all types of lenses for many years.... and its truly remarkable when the set-up is right, how it confirms the math and often the MTF values the makers provide. This is for both film and digital. ... Chris Perez has done an excellent job testing lenses of all types, I am sure you have seen his web site? His results concur with everything I have ever tested.
http://www.hevanet.com/cperez/testing.html
Thank you again Chris for being such a big supporter of the LF community.


He is legendary.



But using common LF lenses, which probably 90% of them in existence, are designed to be shot at f22 - 45, their is such a large inherent slop factor, in the end...the means don't justify the ends. If you follow this forum, you will see this issue surface every few years.


No. You View Camera Folks love to work in that sloop. After you have framed
the perfect shot, whip out the clear class and scopes. Photography will never be
the same for you. You will become even more of a devotee than you are now.

Who knows, maybe you will be the first one to send one back. I'd send you
a bottle of wine if that turns out to be the case.



I think a more obvious area of attack to improve image quality is the squareness between the front and back standards, specially with short fl lenses shot at f8 - f16. As slight un-squareness presents huge variances in the focal plane vs. the film plane. Of course, this problem is magnified in 8x10 vs. 45.


We just need a piece of metal with fine set screws to hold the glass plenum
to calibrate it (achieve best possible focus). Then ether the film holders
or camera back could be shimmed. With some higher end cameras its probably
best to have it serviced at the factory.

Ill continue in the next post ;)

rvhalejr
31-Dec-2008, 00:08
Continued from previous post

QUOTE=bglick;425233]
Comments on your 2nd post....
A good test, to reduce testing time, is to first test the lens with a digital back. I have a set-up that enables a DSLR to mount as a film holder. This gives you a "sure" flat recording plane, and a great focus mechanism, as I use after-market focusing screens sold by Katz Eye Optics - with these screens you can really nail the focus to the levels of accuracy you desire. [/QUOTE]

Great !!! You have the 90 degree line of sight dialed in. But Inspecting through
clear glass at 75 and 65 degrees (for 4x5) will take you to another level of understanding.

As you may already know my work is based on the Charles Sleicher manuscript
that accompanied his lens test chart. His work was the first I came across
that described using a microscope in the film plane to measure lp/mm and give
the 500 lp/mm value for the SLR 50mm f1.8 lens formula.

I verified that with my own microscope and published the picture a long time
ago (the site is long gone). 500 lp/mm is an amazing thing to see . Sadly, many seem to dislike the idea as well as micro-photographs, the fact an alternative
method might exist seemed to annoy a lot of people. I'm Agnostic, its just another tool, maybe helpful for some things and certainly not a solution for everything.



Now you have a basis to compare film with... Digital recording is subjected to the same 1/R curse....(which is Nyquist theory in action) of course, SWA and even some WA lenses will not perform well with most digital sensors, as this still a weak link in digital sensors....

Anyway, we all are interested in your findings.....

Thanks for all the kind words and help with view camera, of which I use but a small
portion of their capabilities. Even though I'm in love with the speed graphic
as a piece of functional art and as iconic symbol for photography in Hollywood
to this day I really respect and appreciate the works created by the large
format view camera community.

I wish people could be nicer (they can get really nasty flame wars going on other
sites) but really appreciate constructive criticism with regard to technique and
theory without which I could never appreciate others fine work as it should be
and (hopefully) improve my own work.

I should consider posting my first manuscript in this forum as it has the disclaimers
in it as to the basic capabilities of the fine focusing kit. Simple things like
I'd rather be caught dead than using Anti-Newton Glass. There is a place for diffusion
filters but AN is something to be avoided (like really gross way over the to wedding pictures - which there are exceptions and I plead guilty to).

Shooting film is very expensive for me right now, so calibrating film holders, plenums and finding a way to hold film flat should save some money that otherwise might be wasted on developed film that is to soft (shooting with a good lens at is highest resolution).

High precision was turned to for the hard, cold straight line architectural look and emulation focusing what Ansel Adams work in Yosemite looks a lot like.

The diffuse soft look is another style I like some times characterized as a glamor,
high emotional image or artsy look (vignetting seems to work well with that).

Whats wonderful about sublte diffusion in Digital and Analog is that it can
increase the signal to noise ratio by a significant amount but
have little or no effect on the smallest detail (as verified by 35X magnification
before shooting).

If You Like very subtle diffusion (with portra and the 65mm SA) and want to
see a similar effect with a digital back magnification at the image plane is a
really big help in choosing the perfect on lens diffuser.

My feeling is that flat film (from connected sources) standard film holders,
calibrated at +/- .002" for 4x5 and +/- .004 for 8x10, clear plenum
shimmed to the same is probably fine for most view camera photographers
out there.

But for Speed Graphic Press Photography fans who appreciate the "brutal

sharpness" found in those photos or exacting resolution in landscape or
architecture may be worthy of a bit more effort as the maximum fstop
for sharpness is (if I understand this correctly) at a point where the
Image Plane envelope of good focus about the emulsion plane approaches
zero.

This is what I have observed up until now. But if the prototype film holder
for forcing film to be flat does no better than a stock (yet calibrated) film
holder with flat film from connected sources then that would be far easier
for me.

And if I do find extreme instances where this is the case I would not recommend
it to anyone unless they found themselves in the same predicament.

So much work to do and so little time (sigh).

Bless us one and All,

Rich Hale (haven't used that one in a long time).

bglick
31-Dec-2008, 11:32
> 3200ppi is the recognized maximum for high end photography (I've seen it from those way more accomplished than I).


Yes, 3200 dpi, / 25.4 / 2 = 63 lp/mm to film, this is possible, BUT ONLY at f2.0 and wider, and that is not reality in LF photography. Run the 1/R equation, it will become quite clear.

I do have some f2.0 lenses that resolve 65 lp/mm, but of course, they are 35mm lenses, they are also "nearly" diffraction limited, and have 18 elements, and weigh 8 lbs, with 100mm wide aperture. 35mm lenses condense their resolution into a tiny projected image circle. LF lenses create large image circles, diluting the resolution over the image circle. When you combine this with the fact LF lenses are only designed at high f numbers, the aerial resolutions favor small formats, in a big way....


1500 / f2 = 750 lp/mm aerial resolution for 35mm lens

1500 / f22 = 68 lp/mm aerial resolution, typical 4x5 application

1500 / f45 = 33 lp/mm aerial resolution, typical 810 application.


As you can see, the 35mm delivers 23x more resolution than the 8x10 lens.


LF gains resolution through film size, unfortunately it can not also hold the optical gains of smaller formats as well - which is the premise you are suggesting. LF looses terribly in aerial resolution due to lenses designed to be used at high f stops. Have you ever seen a diffraction limited f2.0 LF lens that covers 8x10? So you have taken the attributes of tiny formats, such as 35mm high end optics, and are trying to combine them with LF film..... we can only wish n pray that such phenomena as this can be played out in the real world...


The rest of your math I agree with, once you plug in realistic ppi numbers for LF. The 3200 ppi example you offer is real, for 35mm camera systems, using the BEST optics ($6k+ lenses) and Velvia color film. In which case, as you suggest, 10MP per square inch is a fair representation of 35mm systems, which when extracted out to 24x36mm format, is equal to 15MP. This is well accepted. Using lower grade color film, of course the number would be closer to the 10MP value. However, you can NOT extrapolate this to LF, before using 1/R as the basis of what can be resolved in that format.


So, using a realistic 27 lp/mm to film, you will produce 27 x 25.4*2 = 1372^2 = 1.8MP per sq. inch, * 20 sq in (4x5) = 37MP. A huge discrepancy from your original 400MP claim, and your more recent claim of 200MP. Of course, you must take each case on its own merits as all LF lenses and film change the variables, but none of these variables will rock the results to achieve your claims. And most importantly, the f stop you shoot at is still the most critical factor for LF. I hope this makes it clearer.




> The 39MP digital backs are actually Monochromatic photo sites, 1 pixel is
ether Red, Blue or one of two Greens.


Agreed, but in the end, this has proven to be a very small liability, vs. if each pixel could read R,G,B. This is accounted for in many comparisons when Bayer sensors are compared to full RGB sensors such as Foveon. The predicting algorithms are so good, the net effect this, might loose 15 - 30% of the pixel count, based on the colors of the subjects. 20% is a good average.




> So we can call the 39MP what is is a full color 10MP camera with a bit level depth of 12


You are over simplifying here. If you want to learn more about this, google the Foveon sensors, which record RGB at each pixel site. They have been compared to Bayer sensors many times, and the "net gain" is MUCH less than the simple math suggest. Part of the reason is, each sensor can sense parts of other colors, as many colors are mixes of other colors. (an abbreviated position on a very involved issue) Of course, this is why a Bayer sensor resolves best with B&W targets, and it resolves much worse with red targets.... all this is well documented.



Bit depth, is a completely different issue..... it determines the levels of tonality within a color. Although there is a slight relationship between bit depth and resolution, its small vs. the major gaps we are dealing with in this discussion.


> Using Monochromatic Digital Back accounting the film 200 RGB Megapixel is actually
600 Mega Monochromatic (less 25% for lack of two greens) is 450 Mega pixels based on monochromatic rgbg photo sites. But 400 seems close enough to make the point.


I have addressed most of this above. However, if you want to implement the pixel color issue into play..... you can reduce the MP of the backs by....


30% whens shooting Red and Blue Targets

15% when shooting Green Targets

0% when shooting B&W targets.


If you have a digital camera with some good lenses, you can test this by shooting a nice array of color targets, and you will see, after 1/R, these reductions above represent the reality of digital recording of Bayers sensors, using at a min. high end DSLR... we are not comparing a $50 P&S digital camera here. (just to be clear) So a good avg. is 20%... again, we are trying to get in the ballpark in this discussion, i.e. somehow tame 600MP claims down to 40MP... .then one can deal with the nitty gritty details. Of course, these discussions have been going on for years on the internet, most of this is old news.


> Admittedly Scheimpflug is out of scope for me. f8-f16 is good for the 35mm or DSLR spotmeter, f11-f22 for 120/220 backs on 4x5, and f32 is good on a sunny day but freezing movment becomes problematic for me.


Scheimpflug has not entered into this discussion, not sure why you mention it.... and as for f stops, I am not following your logic here. A 35mm camera that requries 5.6 for sufficient DOF, will use f11 on MF, f22 on 4x5 and f45 on 810.... maybe what you wrote above was a typo? Simple rule, you double the format size, you double the f stop for the same DOF.



> Depth of Focus has some value (probably much more to view camera purists), but I have to to resist relying on it as an excuse to not shim the plenum so as to bring Image Focus into the Emulsion Plane.


Yes, both camera manufacturers, film holder manufacturers have done this for us, hence why there is international standards for all these issues. Unless something fell out of alignment, or you are dealing with early 1900's cameras with modern film holders, Depth of Focus at the film plane will resolve any small errors, as suggested in my previous post, by a factor of 15 - 20x, vs. the .001" you are shooting for.

end of part I

...

bglick
31-Dec-2008, 11:33
Part II



> I think .001" (as a goal) is just good precision (thats why my fan club is in Germany) leaving the other .014" to be used by the view camera photographer as they see fit.


As you can tell, I am a stickler for precision. But the precision has to have a desired end effect. I think you are overlooking the fact these issues have been addressed for many years and have surfaced in the products we use....then, Depth of Focus is the reason more precision will not benefit the final product, UNLESS, you have defective equipment, or you are shooting at f8 or wider on LF.... not sure if I explained this well enough...


> No. You View Camera Folks love to work in that sloop. After you have framed
the perfect shot, whip out the clear class and scopes. Photography will never be
the same for you.


you are missing the point Richard. The "slop" is inherent in the physics behind the optics. The slop allowed in the system, is a result of the principles behind Depth of Focus at the film plane. This is optics fundamentals at play, you have confused this with slopy users, slopy cameras, etc. You are trying to take a tolerance set by Depth of Focus, for example of +/- .015", whereas inside this tolerance range, there is no gains to be had, and you are trying to tighten that tolerance to +/- .001". You are ignoring the fact optical principles of Depth of Focus will not allow added gains with tighter tolerances. However, your system would be useful for fast 35mm lenses.


> As you may already know my work is based on the Charles Sleicher manuscript
that accompanied his lens test chart. His work was the first I came across
that described using a microscope in the film plane to measure lp/mm and give
the 500 lp/mm value for the SLR 50mm f1.8 lens formula


BTW, Charles makes a great lens test chart if anyone is interested, and its only about $35. Lets address this 500 lp/mm issue. First, a diffraction limited f1.8 lens can deliver 1500/ 1.8 = 833 lp/mm max. I am using 1500 for an avg. of the color spectrum. But in reality, NO lens at f1.8 at 50mm fl is diffraction limited, its at best, 50% of this value.... so these numbers are just tooo high. The only "near" diffraction limited lenses need to be in the very long fl's, 200mm+, as at these fl's they do not have to contend with the sharp ray angles the normal to WA lenses deliver. This is another optical fundamental shortcoming that will not be overcome in our lifetime. This is why high end refracting telescopes are usually diffraction limited, as their fl's are 500mm+, and yet they only contain 2 or 3 elements, and yet a Zeiss WA lens will have 17 elements and will never be a match to the resolution of a telescope. Sad, but true, photography puts very hardcore constraints on optics designs.



> 500 lp/mm is an amazing thing to see .


The human eye can see a max. of about 1 arc minute. To translate this into lp/mm, requires introducing distance....which can vary. But regardless, the best eyes can resolve 7 - 10 lp/mm, avg. eyes 3 - 5 lp/mm and aging eyes 1 - 3 lp/mm. Even trying to view 500 lp/mm under magnification, it would require for an avg eye, 100x magnification to produce 5 lp/mm at the eye...or about a 2mm fl eyepiece.... is this what you did?


> Shooting film is very expensive for me right now, so calibrating film holders, plenums and finding a way to hold film flat should save some money that otherwise might be wasted on developed film that is to soft (shooting with a good lens at is highest resolution).


IMO, using optics to check alignment is overkill and has too many variables that can produce poor results. You can accomplish film flatness and alignment much easier with precision straight edges and dial gauges. Since they are precisioned so fine, and in mass use in the metals working fields, you can acquire this gear cost effectively, not rely on all the diffraction low cost optics present, and also remove the human eye from the equation, as everyone does not have perfect vision. You also have the big factor of what focus plane the optics itself is focusing on. (too long to discuss here)


I have used a high precision straight edge and .0001" dial gauges and checked all my LF cameras and film holders through the years.... all of them were remarkably accurate, no shims required anywhere. Granted most of my gear was bought new in the past 10 years, I only use Toyo film holders. My point is, I think there is better methods to accomplish your task.... i.e. more accurate, similar cost, and repeatable and eliminates the human vision variable.



> My feeling is that flat film (from connected sources) standard film holders,
calibrated at +/- .002" for 4x5 and +/- .004 for 8x10


i addresses this in my previous post.... these numbers are overkill for the common f stops used in LF photography...



> And if I do find extreme instances where this is the case I would not recommend
it to anyone unless they found themselves in the same predicament.


Rich, I am sure your intentions are sincere, which is often the case within the LF community. I hope you don't find my comments offensive in anyway. This is tricky stuff, and many people can fool themselves when it comes to these issues, they are complex. I deal a lot with optical engineers and have been involved in designing many optics, as well as being a life long photographer. Sometimes knowledge in these areas is hard to find, at any level. And with the internet being filled with more mis information vs. useful information, it sometimes makes it more difficult to get to the right answers to a given task. hopefully I have shed some light on the work you plan to do.

bglick
31-Dec-2008, 13:11
Several years ago, I posted a graph I made that demonstrated the resolution potential between the formats. I should probably update it, as when I made it orginaly, the pixel counts that would finaly surface were different vs. what I used. But regardless, it shows the film comparisons as well.

http://www.pbase.com/bglick/image/50899836/large

You can see, at infinity focus, last set of bars to the right, the 810 format holds a substantial resolution gain over all the other formats, including digital.

However, the bars next to the infinity bars show the formats when the image required a relatively high f stop to accommodate depth of field in the image. In which case, MF, 45 and 810 are relatively close to each other in terms of net resolution when comparing equal size final prints. This demonstrates what I referred to earlier.... there can be NO generalizations made when comparing format sizes, OFR, film vs. digital, etc. All things must be taken into consideration for each comparison. The variables have a radical change on the results / comaprisons.

An extreme example.... if you view the last set of blocks, (infinity focus), you can see 810 will out resolve 35mm, 13MP, (at the same size final output) by 23/4 = 6x. But in the next set of bars, where equiv. f stops are used for each format due to DOF, the 810 can only out resolve 13MP at 10/4 = 2.5x. All these charts assume color film using targets of a contrast ratio that yield 80 lp/mm MTF.... (Velvia)


While this discussion brought in 35mm lenses (albeit their performance was confused with LF lenses) .... today, these 35mm optics are beyond remarkable. While LF lenses are, and always have been somewhat limited by diffraction, 35mm lenses were not limited by diffraction - so we continue to see tremendous advances in optical quality... they just keep improving. Consider a very low contrast subject like this link below.... and hand-held at 200mm.... with a low end DSLR, and yet it can resolve like this?? And for a $900 lens ?... truly amazing...

http://www.pbase.com/bglick/image/105272354

rvhalejr
31-Dec-2008, 14:18
> 3200ppi is the recognized maximum for high end photography (I've seen it from those way more accomplished than I).

Yes, 3200 dpi, / 25.4 / 2 = 63 lp/mm to film, this is possible, BUT ONLY at f2.0 and wider, and that is not reality in LF photography. Run the 1/R equation, it will become quite clear.


Is this the same 1/R equation found in the Appendix of this manuscript ?

diglloyd.com/diglloyd/free/sleicher-res-chart/SleicherResChartInstructions.pdf



35mm lenses condense their resolution into a tiny projected image circle. LF lenses create large image circles, diluting the resolution over the image circle. When you combine this with the fact LF lenses are only designed at high f numbers, the aerial resolutions favor small formats, in a big way....

1500 / f2 = 750 lp/mm aerial resolution for 35mm lens

1500 / f22 = 68 lp/mm aerial resolution, typical 4x5 application

1500 / f45 = 33 lp/mm aerial resolution, typical 810 application.

As you can see, the 35mm delivers 23x more resolution than the 8x10 lens.


If 33lp/mm is all one can get out of 810 then I'd guess (never have used one
although they themselves are beautiful functional art) that any kit to help
sanity check alignment and perform calibration would be futile if not wasted
effort :(



LF gains resolution through film size, unfortunately it can not also hold the optical gains of smaller formats as well - which is the premise you are suggesting. LF looses terribly in aerial resolution due to lenses designed to be used at high f stops.


Suggestion in the context of an avid photographer wondering "why or why not".
Not in any Engineering sense UNLESS it holds up under repeatable testing.



The rest of your math I agree with, once you plug in realistic ppi numbers for LF. The 3200 ppi example you offer is real, for 35mm camera systems, using the BEST optics ($6k+ lenses) and Velvia color film. In which case, as you suggest, 10MP per square inch is a fair representation of 35mm systems, which when extracted out to 24x36mm format, is equal to 15MP. This is well accepted. Using lower grade color film, of course the number would be closer to the 10MP value. However, you can NOT extrapolate this to LF, before using 1/R as the basis of what can be resolved in that format.


No, I'm NOT extrapolating this to anything larger than 4x5 (not 810 or ULF with which I have no experience). Arguably some do not even consider 4x5 LF and when I use a 120/220 back ***OR*** 2x3 format I'm not sure I am either.

Anyone would have a hard time convincing me that Ziess, Scheinder, Nikon APO
lenses versions that rock at 2x3 should not at least be carefully examined in the 4x5
versions.

Hopefully it is recognized that a 2x3 lens with movement will have none at 4x5
and that those who do not consider "Ariel" or lack of movement LF Photography
are not offended.

To me 4x5 is sort of a a miniature LF and the number value of 68 lp/mm seems within the realm of possibilities (maybe dead on for your high quality film, equipment and experience).

That does not mean that it should not or cannot be subjected to repeatable
testing for potentially higher values.

Furthermore, it would seem prudent for little people like my self to sanity check our 1949 vintage gear (yes I rebuilt the focal plane shutter by hand and am proud of it and the history that it represents).



So, using a realistic 27 lp/mm to film, you will produce 27 x 25.4*2 = 1372^2 = 1.8MP per sq. inch, * 20 sq in (4x5) = 37MP. A
huge discrepancy from your original 400MP claim, and your more recent claim of 200MP. Of course, you must take each case on its own merits as all LF lenses and film change the variables, but none of these variables will rock the results to achieve your claims. And most importantly, the f stop you shoot at is still the most critical factor for LF. I hope this makes it clearer.


Sorry if if my huge discrepancy offend anyone, I have no vested interest in digital backs, really expensive photo equipment, etc.

And no (as indicated above) anything less that 70lp/mm is not what I'm generally looking for is high resolution. Any Validation Engineering lp/mm results that do not hold up to a microscope sweeping through the emulsion plane should be called into doubt as a matter of generally accepted good scientific practice.

In another life I worked on a project called the Hubble Space Telescope. No way
would NASA allow us to open up the roof and check the optics because they
knew better. So it went up on orbit and could not focus on a damn thing.

I WILL NEVER BE PUT THAT POSITION AGAIN !!!

The problem many well paid Engineers at large camera and photography related firms
is this. The Microcope and Stand setup to quantify lens resolution has become
very cheap. Anyone can outfit a lab for as little as $3000 (probably a tenth of
what some hear drop on thier systems) and verify marketing claims (unless they
have a closed black box system). This means the numbers can now be easily
verified - should be no problem if they are accurate an repeatable.

So why all the fuss about a little verification and validation ? Beats the hell out of me .,.



> The 39MP digital backs are actually Monochromatic photo sites, 1 pixel is
ether Red, Blue or one of two Greens.

Agreed, but in the end, this has proven to be a very small liability, vs. if each pixel could read R,G,B. This is accounted for in many comparisons when Bayer sensors are compared to full RGB sensors such as Foveon. The predicting algorithms are so good, the net effect this, might loose 15 - 30% of the pixel count, based on the colors of the subjects. 20% is a good average.

> So we can call the 39MP what is is a full color 10MP camera with a bit level depth of 12

You are over simplifying here. If you want to learn more about this, google the Foveon sensors, which record RGB at each pixel site.

They have been compared to Bayer sensors many times, and the "net gain" is MUCH less than the simple math suggest. Part of the reason is, each sensor can sense parts of other colors, as many colors are mixes of other colors. (an abbreviated position on a very involved issue) Of course, this is why a Bayer sensor resolves best with B&W targets, and it resolves much worse with red targets.... all this is well documented.


I respectfully disagree with the Foveon citation. The only valid comarison for
engineering purposes are the photon-multipliers used in Heidelberg Tango Wet
Scans.



Bit depth, is a completely different issue..... it determines the levels of tonality within a color. Although there is a slight relationship between bit depth and resolution, its small vs. the major gaps we are dealing with in this discussion.

> Using Monochromatic Digital Back accounting the film 200 RGB Megapixel is actually
600 Mega Monochromatic (less 25% for lack of two greens) is 450 Mega pixels based on monochromatic rgbg photo sites. But 400 seems close enough to make the point.

I have addressed most of this above. However, if you want to implement the pixel color issue into play..... you can reduce the MP of the backs by....

30% whens shooting Red and Blue Targets

15% when shooting Green Targets

0% when shooting B&W targets.


Thanks for pointing that out, its rare that anyone will mention that color
targets engineered to test design weaknesses do yield poor results.



If you have a digital camera with some good lenses, you can test this by shooting a nice array of color targets, and you will see, after 1/R, these reductions above represent the reality of digital recording of Bayers sensors, using at a min. high end DSLR... we are not comparing a $50 P&S digital camera here. (just to be clear) So a good avg. is 20%... again, we are trying to get in the ballpark in this discussion, i.e. somehow tame 600MP claims down to 40MP... .then one can deal with the nitty gritty details. Of course, these discussions have been going on for years on the internet, most of this is old news.


600MP does need taming (now that the true context of 40MP as been re-stated accurately). From an engineering test perspective I'm uncomfortable assuming
that given the 1/R equation, microscopes sweeping the image/focal/emulsion
plane that there does not exist an optic/film combination lying between
the 40MP and 200MP value.

For strict metrology engineering lab values (nothing the public will see) the 10MP
value and 12bit depth is probably going to stick until repeatable tests demonstrate otherwise.

Futhermore, it is implicit that Industrial and Scientific Tests of the DB should be done raw so that software (an admittedly extremely powerful factor) does not skew highly precise and repeatable measurements.

rvhalejr
31-Dec-2008, 14:20
Continued from previous post (ran out of room) .,.



> Admittedly Scheimpflug is out of scope for me. f8-f16 is good for the 35mm or DSLR spotmeter, f11-f22 for 120/220 backs on 4x5, and f32 is good on a sunny day but freezing movment becomes problematic for me.

Scheimpflug has not entered into this discussion, not sure why you mention it.... and as for f stops, I am not following your logic here. A 35mm camera that requries 5.6 for sufficient DOF, will use f11 on MF, f22 on 4x5 and f45 on 810.... maybe what you wrote above was a typo? Simple rule, you double the format size, you double the f stop for the same DOF.


I'm trying to keep the model as simple as possible (my head hurts).

Scheimpflug is way over my head (so thanks for not goingthere).

I do not think Depth of Focus is of any use on small and medium format cameras
because in lies in the emulsion plane (and therfore is zero).

I believe that it is generally accepted principle that with no movements the
depth of focus on a 4x5 can also be zero, which also happens to be the point
where maximum resolution is achieved.

This seems to be disliked by view camera purists. But there are just enough
movements (if you know what you doing) to have a little fun on a press camera
(speed graphic). I know the Toyo is way better but suspect that a 35x loupe
in the image plane will help resolve an airy disk to as close a point as possible.

This could not be done with much accuracy behind Beattie and Fresnel sceens
(with DOF at zero) maybe some of the newer screens would allow this (would
be nice) so all you would need would be the carson 35X pocket microscope
which I think is under thirty dollars now.



> Depth of Focus has some value (probably much more to view camera purists), but I have to to resist relying on it as an excuse to not shim the plenum so as to bring Image Focus into the Emulsion Plane.

Yes, both camera manufacturers, film holder manufacturers have done this for us, hence why there is international standards for all these issues. Unless something fell out of alignment, or you are dealing with early 1900's cameras with modern film holders, Depth of Focus at the film plane will resolve any small errors, as suggested in my previous post, by a factor of 15 - 20x, vs. the .001" you are shooting for.

end of part I

...

The only thing I want from Depth of Focus is for it to be zero as to attain the highest
lp/mm measurement possible on a 4x5 with no movements and (if affordable) APO
lenses.

bglick
31-Dec-2008, 15:54
> Is this the same 1/R equation found in the Appendix of this manuscript ?


A more complicated version of this formula, which I have not checked, is found on page 8 of the pdf link you provided. The 1/R equation I used, was explained in detail above.... there is several versions of 1/R, most all producing similar results, at least considering the mega differences this thread is evaluating. Basic 1/R refers to non macro of course.



> If 33lp/mm is all one can get out of 810 then I'd guess (never have used one although they themselves are beautiful functional art) that any kit to help sanity check alignment and perform calibration would be futile if not wasted effort


Or, just simply buy $100 worth of straight edges and dial indicators, and with a little mechanical know-how, you can do simple sanity checks for what you were pursuing.... the more precision you require, the more expensive the test gear. There is a few companies such as Toyo USA that will laser check your cameras, and align them for a reasonsable fee. The problem often is in the film holders, assuming they are not modern ones which were not abused...



> No, I'm NOT extrapolating this to anything larger than 4x5

my point was, you can't even extrapolate up to 4x5.... my previous post explained this in detail....




> To me 4x5 is sort of a a miniature LF and the number value of 68 lp/mm seems within the realm of possibilities (maybe dead on for your high quality film, equipment and experience).


With color film, as I mentioned in my previous two posts, OFR (On Film Resolution) is closer too 27 lp/mm. This assumes 65 lp/mm MTF for the film and f32, just as an example.... the 68 lp/mm you refer to is for lens aerial resolution, i.e. not combined with film, which is where 1/R enters into the equation. The lens aerial resolution measures the MTF value of the optic only. This was just for clarification, as based on what you wrote, I was unsure if this was clear....


> Furthermore, it would seem prudent for little people like my self to sanity check our 1949 vintage gear (yes I rebuilt the focal plane shutter by hand and am proud of it and the history that it represents).


Yep, very valid point. If you do a search on this forum, you will find the dates when international standards came into play... I don't recall... but it was a long ago.... anyway, there is a lot more than gg and film alignment, and film flatness to deal with when checking a vintage camera. The alignment between the two standards is equally (if not more) important. These cameras can take a beating over the years.



> And no (as indicated above) anything less that 70lp/mm is not what I'm generally looking for is high resolution. Any Validation Engineering lp/mm results that do not hold up to a microscope sweeping through the emulsion plane should be called into doubt as a matter of generally accepted good scientific practice.


Agreed, but be sure to check the film plane with a high quality optic, otherwise you will have introduced a new weak link in the chain. A good scaner, such as a drum or high end flat bed is usually good enough, but a microscope is even better, considering you have good vision...



> The Microcope and Stand setup to quantify lens resolution has become very cheap. Anyone can outfit a lab for as little as $3000 (probably a tenth of what some hear drop on thier systems) and verify marketing claims (unless they have a closed black box system). This means the numbers can now be easily verified -


Are you referring to examining film, or aerial resolution of lenses?


> I respectfully disagree with the Foveon citation. The only valid comarison for engineering purposes are the photon-multipliers used in Heidelberg Tango Wet Scans.


Just an FYI.....The Tango Wet scans are by no means a high-end standard today.... there is a host of scanners that supersede what a Tango can do, even high end flat beds, from Creo and Screen. Tango drums were all the rage, but in mid 90's...



> Futhermore, it is implicit that Industrial and Scientific Tests of the DB should be done raw so that software (an admittedly extremely powerful factor) does not skew highly precise and repeatable measurements.


Software is an integral part of the Bayer system. The test results I use, and the ones I cited above all use RAW processing and sharpening. The same is true for scanned film, as this is the situation in the real world, i.e. both images are manipulated to their best possible form. (assuming one is not printing with a darkroom enlarger) Since a Bayer file is 80%+ interpolated data, removing software will cripple its capabilities vs. running it through the software mill, which it was designed for.


> I do not think Depth of Focus is of any use on small and medium format cameras
because in lies in the emulsion plane (and therfore is zero).


I think Zeiss, Leica and Mamiya would strongly disagree with your assertion. They have written numerous white papers through the years stating just how critical film flatness is.... you can find them on the web if you search hard enough. But once again, this is due to their camera systems optimizing lenses in the f1.x - f5.6 range. The Mamiya 7 camera is praised not just for its lenses, but for its extreme film flatness, producing 35mm type resolutions in a MF body.


> This could not be done with much accuracy behind Beattie and Fresnel sceens (with DOF at zero) maybe some of the newer screens would allow this (would be nice) so all you would need would be the carson 35X pocket microscope which I think is under thirty dollars now.


The problem with checking anything with a LF ground glass is the simple fact - a ground glass is VERY low resolving... in the 1 - 6 lp/mm range at best. Glass can be ground finer to resolve better, however then it will transmit too much light through the glass and the image will be loose light intensity, making composure nearly impossible under the hood. It's a trade off..... But this is why anything more than a 5x loupe on a gg is way overkill.... the glass itself the limiting factor. Fresnels complicate the matter even more, as they re direct light.


If you want a high resolving glass screen you should use a 3 micron fiber optic plate which will resolve 150 lp/mm, now you can use a high quality magnifier to inspect the image appearing on the fiber optic plate. I once considered this..... I had a spec. prepared and sent it to a few optical fabricators... for 4x5 size, prices ranged from $5k - $10k and for 810....not worth mentioning. Too rich for my blood... not too mention, it would only be for critical inspection of the point of exact focus, not for composing, as it would transmit the image through the plate, not capture it.



> The only thing I want from Depth of Focus is for it to be zero as to attain the highest lp/mm measurement possible on a 4x5 with no movements and (if affordable) APO lenses.


Depth of focus has no true Zero, UNLESS, you are shooting a flat subject or an infinity subject. This is where film alignment and gg alignment becomes critical, but again, only at wider f stops, say f8 or wider.


When shooting a common scene, such as a landscape, which has depth.....then the Depth of "Field" of the subject side of the lens, say 40 ft to infinity, this translates to a compressed range of focus at the film plane.... in this case, a .07" range, which correlates to 40ft to infinity. This assumes a 150mm fl lens. Where the film plane lies, dictates at what distance from the lens, critical focus is achieved. When you consider all the slop in the mechanics of a LF system, the trueness of the standards, the gearing, the lock downs where slight movements occur, etc. .07" is easy to be consumed, hence why high f stops are almost mandatory in LF....... If you compare the precisioned movements on a high end studio view camera for MF digital backs, vs. a LF field camera, its quite obvious how sloppy things really are.... at least when compared to precision variables we are discussing here.


see next post....

bglick
31-Dec-2008, 15:55
Rich, you may find it interesting, ...... what you are trying to accomplish here, (gg / film alignment) is now standard in Canon DSLR's. They now incorporate focus setting offsets you can enter into the cameras memory. After you test for this for a given lens, and make the critical adjustments, every time you use THAT lens, the the plane of sharp focus you see through the viewfinder (our gg), will be perfectly aligned with the digital sensor plane. Such a nice feature, who would have ever imagined this type of technology would be built into consumer grade DSLR's. ???


Of course, with f2 lenses common on these systems, this becomes a very desirable feature. At f2.0, the Depth of Focus at the film plane is about +/- .0015". As you can see, at these LOW f stops, correcting errors at the film plane of .001" is very desirable and EXTREMELY beneficial. But at f32 on LF, the Depth of Focus at +/- .0415", is quite sloppy, about 30 x more sloppy.


There is a good write up on this on the luminous landscape web site.... it also shows a neat product that helps you determine critical focus by taking exposures....this is the same technique I used to confirm my lenses.... this new "lens align" product is ideal for fast and easy digital camera testing of sensor / viewfinder alignment. have a look....

http://tinyurl.com/5pot3p

Nathan Potter
31-Dec-2008, 17:11
bglick, you described a fiber optic plate above that I am not at all familiar with but sounds pretty interesting. Is this an array of fiber optics (3 um in diameter) all set side by side in an array that could be fabricated in 4X5 format? As such the at focus end of the fiber array could capture the image and transmit it on axis to the rear exit of the array. If the fiber sections are clear that would only produce an aerial image that would need to be intercepted by a loupe focused on the front of the array or the rear of the array? (I think the front, but maybe it does not matter). OTOH the front could be ground finely to produce a real image and the scattered light from that surface would tend to be transmitted on axis back to the loupe. If I'm imagining this correctly the result would be an impressively bright digital screen so to speak. I realize that such a device would be necessarily expensive to produce but sounds as if it would be the cats ass for redirecting off axis rays, especially for wide angle lens applications. I might settle for 10 um fibers at a lower cost (1/10 the number of fibers).

I was interested in the lens align product also - pretty cute. It would appear that a version could be used for LF purposes. The advantage would be that one need not futz with the method discussed above so much but use the device in the center and corners of the film plane for a particular lens. Of course the practicality of the exercise can still be called into question given the plethora of hard to control variables endemic with view cameras.

Another point here as discussed above is DOF. DOF requires one to establish an acceptable Circle Of Confusion prior to strictly defining a Depth Of Focus. Which leads me to another point that I confess I'm fuzzy on. I have always assumed that a point of best focus for an ideal lens is the diameter of an Airy disk and that this point along the image axis is a point that tends to an infinity point. In other words the depth of this point is infinitely small. Any light you can shed on this? It won't help my photography but is intellectually interesting.

BTW this is an interesting post and discussion even tho interlaced with considerable hype. Great thanks for the interaction from both of you.

Nate Potter, Austin TX.

rvhalejr
31-Dec-2008, 19:58
...
I have always assumed that a point of best focus for an ideal lens is the diameter of an Airy disk and that this point along the image axis is a point that tends to an infinity point. In other words the depth of this point is infinitely small. Any light you can shed on this? It won't help my photography but is intellectually interesting.



By Jerry Lodriguss "Astrophotography Techniques"
Ref: astropix.com/HTML/I_ASTROP/FOCUS/DEFS.HTM

Spot Size of the Airy Disk
d = 2.44 x lambda x f -- OR --
d = 0.001586mm x f

Linear Diameter of the Airy Disk (f/22 to f/128 added - see attachment),
I think this is right .,.

Maybe it partially explains why my laser pointer does not look like a perfect point.

Richard

bglick
31-Dec-2008, 20:08
> Is this an array of fiber optics (3 um in diameter) all set side by side in an array that could be fabricated in 4X5 format?


This is EXACTLY correct..... Fiber Optic Plates (FOP) can be made with any size fibers, (with 3 micron being about the smallest) and almost any size format, and at any thickness as well. I have made them for different optical products through the years.... however, as they get big, the price becomes exorbitant....as most FOP's are the size of a dime... a big one is the size of a quarter...


> If the fiber sections are clear that would only produce an aerial image that would need to be intercepted by a loupe focused on the front of the array or the rear of the array?


The focus plane is at the front, and is transmitted with virtually no loss in resolution to the rear of the array....where you can use the loupe, its amazingly effective. In the right application, I have used them in between two lenses, and the FOP become s invisible.... but they have 3 micron fibers (1/1000th of a mm). Their purpose is to change the ray angles without sophisticated / expensive optics. They are also used to re direct the location of the plane of sharp focus.



> If I'm imagining this correctly the result would be an impressively bright digital screen so to speak.

Yep, this is true, however, FOP's have an inherent f number, and this is based on several factors.... but like all optics, they eat light, and often this makes their use undesirable when light is limited. But for a gg, this is not such a big deal, at least during daylight hours and say f5.6 lenses.


> I realize that such a device would be necessarily expensive to produce but sounds as if it would be the cats ass for redirecting off axis rays, especially for wide angle lens applications. I might settle for 10 um fibers at a lower cost (1/10 the number of fibers).


You can re direct the rays, and that is part of the beauty of FO in general.... but to accomplish what you desire, I don't think the means will justify the ends. First, the highly angled rays on a WA lens already suffer light loss.... they will loose even more light, maybe up to 2 stops additional. Next, to optimize this process, you would need angled fiber optic strands, to intercept the rays dead-on from the lens, then re direct them to hit the film perpendicular. Net effect IMO is..... loss of light, and marginally better image quality...and such a bundle would be about 5x the price I mentioned above...as this is the edge of technology.

have a look at this pix.... its very close to what you desire.....

http://www.us.schott.com/fiberoptics/images/bee_400-220.jpg


> I was interested in the lens align product also - pretty cute. It would appear that a version could be used for LF purposes. The advantage would be that one need not futz with the method discussed above so much but use the device in the center and corners of the film plane for a particular lens.


I invented my own version of this 10 years ago, and used it to assure all cameras and film holders were true.... it cost a fortune in film / processing.... I used rear shift and rise / fall to take multiple shots per sheet film to confirm...luckily everything was dead-on, otherwise, I would have had to do this exercise over and over till it was tweaked just right with shims. Later, I used the machinist method for checking everything, much easier, and more reliable, as you say, it eliminates all the other variables. Its best to isolate all the variables when testing. But, with digital, all this feedback is instantaneous. specially when tethered to a pc...... How sweet, huh..... hence why digital is amazing....


> I have always assumed that a point of best focus for an ideal lens is the diameter of an Airy disk and that this point along the image axis is a point that tends to an infinity point. In other words the depth of this point is infinitely small. Any light you can shed on this? It won't help my photography but is intellectually interesting.


I am not sure I am following your question.... but I will take a stab at it... forgive me if I repeat things you already understand. The point of sharpest focus, is where the rays converge to their smallest point, creating the smallest airy disk. Where this point lies, depends on several factors.


Lets take a LF lens for example... as the complicated zoom lenses that have internal focus introduce many variables beyond the scope of this discussion. A single fl lens has one fl, and no single focus point. The reality is, we don't actually focus our view cameras, there is no such thing as "focus" to a lens. Lets assume rear focus cameras for simplification. The lens remains still, it performs no function when you focus the rear. It projects all subjects in front of the lens towards the film. Near subjects converging rays are further behind the lens, vs. infinity subjects. By moving the rear standard up n back (focus) we simply align the gg to intercept the converging rays to produce the sharpness we desire. The wider the apt. of the lens, the greater the converging angles, the smaller the distance of convergence that meets the cc criteria you desire to achieve. This is Depth of Focus. Depth of Field also exist at the film plane .... as all subjects are projecting converging rays at different points in front of and behind the film plane.


Thats the basics....but how small the convergence becomes (airy disc diameter) depends on many other factors, unfortunately. But the ceiling is set by apt. diffraction, which is why see this mentioned so often, but this is simply a ceiling, not a true value for all lenses. A LF lens not only has ONE fl that never changes, it also has ONE focus distance it is optimized for, where the airy discs will be the smallest, and also ONE or maybe two F stops where the airy discs are closest to the limits of apt. diffraction. The reason for this is.... all lenses are designed with certain input criteria, such as subject plane distance, image plane distance, stop diameters (apt.), image circle size, etc. This is the basis of the lens design.... after this is accomplished, the designer evaluates how bad the image becomes when you wander from the "design conditions". This determines if a lens design is suitable for a given task. As a general rule, the better a lens performs at the design condition, the worst it will perform at non-design conditions. This is why we have makro lenses, as a lens can not be optimized for infinity AND close focus. This is also why lenses should be shot at their design f stops...or higher, as there often is little or no penalty for raising the f stop, as apt. diffraction becomes the limiting resolution factor.


So the point is, the smallest airy disk a lens can produce is not cut n dry... as a general rule, it will exist at the design subject distance, at the design f stop, and often closer to on-axis vs. off axis. This subject distance could mean infinity, or 6" from the lens, or at f5.6 or f32.... this is what MTF charts tell us....unfortunately, IMO, they don't give us enough charts, but some are better than none... Schneider is getting better at this, Rodenstock still far behind.


Of course, then you have to hope the lens was built to spec and tolerances were held, then tested to confirm aerial resolution. I know this is the case with the new digitar lenses. I don't think this is the case with LF lenses.... hence the bad batches you hear about, such as the SSXL 80's several years ago. There reaches a point where makers just gamble on QC, otherwise lens prices can start doubling very fast.... I think LF lenses are a bargain, all things considered.... Today though, computers have sped up the lens QC procedures, within a few minutes a lens can be analyzed for MTF at different focus distances and f stops, distortion plots, image circle diameters, back focus distance, coma, astig., etc. etc. Most all the big makers today use this equipment. Prices have fallen dramatically in the past 5 years.


There is one other caveat.... everything mentioned above assumes spherical elements...the norm up to 5 - 10 years ago. Aspherical elements change all the rules. Their biggest benefit in camera lenses is their ability to level resolution for on axis vs. off axis rays. In some ashperical element lenses, we can see sharper edges than we see in the corners. This is often desirable, as the center area of an image is only a small % of the total image area. Anyway, just wanted to mention aspherics, as they are playing a big role in modern photo optics. Is anyone aware of LF lenses with ashperics elements being used? I think I recall seeing a few advertised?

Nathan Potter
31-Dec-2008, 23:12
bglick, many thanks. I think you inadvertently answered my question which referred to an Airy disk. I was not very precise in formulating the question.

I clearly get your point about light loss when trying to use a Fiber Optic Plate to transmit strongly off axis rays; DUH. One needs to capture a ray orthogonally to the face of the fiber to achieve maximum transmission.

I was not after the diameter of the Airy disk formed by a lens of a particular NA but wondering more mathematically about the length along the optical axis (that is if you will its equivalent depth of focus) for an object which is in a single plane and for, ideally, using monochromatic light. Thus setting the conditions of a single object plane and monochromatic light the depth of the Airy disc along the optical axis will be about infinitely small. Of course using the whole visible spectrum red and blue will fall slightly in front of and slightly in back of the plane of best focus for green depending on the degree of color correction of the lens. And also objects further behind and closer to the lens will be imaged sharply in front of and behind the plane of best focus chosen that I mentioned above. All this you have alluded to above.

I think rvhalejr answered my same question thinking that I was referring to the diameter of the Airy disk. Sorry to mislead.

The only LF lenses which employ aspheric elements I am aware of are the Super Symmar aspheric series I think introduced about 2000. There is the 80, 110, 150 and 210 at least and maybe a couple of other exotics. And indeed I believe the aspheric element or maybe elements are used to improve the far off axis resolution.

Nate Potter, Austin TX.

rvhalejr
1-Jan-2009, 12:48
I've never really studied Depth-of-Focus and what happens to an Airy Disk on a
4x5 system. It does seem to be a big issue now (DOF - not Depth of Field), so
I'm going to measure it when time permits.

Preferred Simple tools are clear glass, 35x Loupe and the 100x with reticule (when there seem to be commonly held opposing views about, well, the validity of anything and everything).

In the off chance that anyone has used a device (like sinar image attached) to
gather lens lp/mm data (about the point of best measured focus) or has seen it published I would like to study it.

The characterization of what the perfect point does in the depth of focus envelope
(observable measurements) help formulate a clear picture from which generalizations might be drawn. I can get data (myself) for incremental changes along the the film plane's normal vector and extrapolate, but that may be to prone to error (and maybe not even reproducible).

I'd like to see it for an intentionally angled rear standard[1] which is is moved in incremental steps along the the film plane's normal vector.

In LF Photography this may follow the "there is no perfect focus" technique by advocated by the pinhole police[2]

What bothers me about the rich and famous here is that they never have the time
to post a picture of flat unexposed film in a film holder with a reflection off the
emulsion that is not distorted.

They have access to MILLIONS of stock photos but just cannot provide such
a simple image, "OH ALL MY FILM IS PERFECTLY FLAT", well fine, then please
show us.

Well leave the "OH IT DOES NOT MATTER BECAUSE OF THE MAGIC Depth
of Focus ENVELOPE" until there is some repeatable direct measurement data
has to what happens to the airy disk in there.

Please try to restrain yourself from condescending remarks. If you disagree then
please do so respectfully[3]. Broad brush characterizations like "hype"[4], etc.
when someone is trying to conduct a simple impartial engineering validation.

Good etiquette need not be ignored[4], even if speculation is considered to be
over the top. There is no top in science as long as step by step directly
measured repeatable data is available to validate a reasonable limit.

For so many to resist (if not hate) the idea of putting magnifying devices in the emulsion plane and then making lp/mm measurements at f-stops known to be the
sharpest speaks volumes.

---------------
Notes

[1] ref en.wikipedia.org/wiki/View_camera

[2] No picture under f64 is an LF picture

[3] This is a "one star thread" by definition the worst of the worst.

[4] I'm ripping up my degree in digital electronics, swallowing it and
eventually depositing it in the same place any ideas that do not
conform to those of the mega pixel police get relegated to.

rvhalejr
1-Jan-2009, 16:12
Ultra Fine Focusing Image and pdf file summary

Posted 1/1/09
1.) Page 2 of 12 - "4x5 Fine Focusing Loupe and Precision Plenum Photography" What happens to a resolution chart with a variance of +/- .012" as compared to and "film plane in optimum position" annotation (a Sinar source)
2.) Table of Linear Diameters of the Airy Disk (f/22 to f/128 added)

Posted 12/24/08
1.) Page 1 of 18 4x5 - "Film Holder and Flatness Metrology" showing unflat film out of the box and distorted reflection of emulsion when placed in typical
wooded film holder (critical dimension .192 - .193).
2.) What a mirror like flat reflected image looks like (rolled and taped to glass plenum in the same way an Heidelberg Tango fluid mount is).
3.) Page 1 thru 4 "The Standoffs for Off-Center Focusing" showing 35x loupe on shimmed plenum with line-of-sight stands for center, middle and corner of frame.

Engineering a Simple Validation Test:
This is setting the ground work for attaining the best possible focus onto
the flattest possible film in a calibrated film holder using resources common
to everyone.

Constraints:
Avoid extreme apertures known to have detrimental
effects on lp/mm measurement.

Whats the hold up ?
Need a source of out-of-the box flat film to test.
A non-distorted mirror image from the reflection on the emulsion out of
the box is needed. If anyone is well connected enough to obtain such
film please contact me.

The non-distorted mirror image is an indication the film is probably
flat to +/- .001" or better.

More time should be spent making bracketed test shots and test time
instead of trying to defend what is logically the next step after repeatedly
snapping in focus across the entire 4x5 frame using aligned glass and
35x loupe.

This should be a fairly boring confirmation of what is already known.
Many seem ready to reject results and attack the validity of the test
if the results conflict with their beliefs.

I plead guilty expressing unrealistic hopes and expectations in some instances. Its based on a big investment in a "Universal upgrade to CCD fluid scanning systems" Should I have to reveal every detail in order for the reader to allow for the possibility ? Off course not. At least not until I can get some really flat focus on some really flat film and determine what the limits are. For all the skeptics know I may be serious about ISO 25, 12 and maybe 6 film if its already flat. Please allow for the possibility that a fresh set of eyes might find something new.

But that does rise to the level or justify disregarding out-of-hand results (before the tests are even started) because they MAY NOT fit the fervently held canonical belief that only two fstops than can be used for Large Format Photography.

The only unbiased conclusion that can be drawn beforehand is that there MAY be an alternative range that could be exploited depending on ones style or desires.

I just want to get the sharpest image possible. Even if the data shows that other f-stops, other than those convention holds we should use, are more precise with respect to lp/mm targets (ariel modality) does not mean that the conventional fstops are deprecated in any way.

So if anyone wants to help out please recommend a source of film known to be flat.

And if you want to criticize then feel free, but you are expected to support your opinion in the same context as this thread. If you have flat film then post a picture.

If your magic DOF (Depth of Focus) justifies something (fstops, non-ariel focus, etc.) then post images, sketches or cite references that illustrate your claim. The use of
DOF to describe Depth of Focus and/or Depth of Field is obfuscation at its worse for
some of us who do not have "i know the context" built into our DNA especially when
they get intermixed (sigh).

I feel like an idiot for even making two 8x10 plenums and prototyping the corner stand. I honestly wondered if AA used this technique and did not tell anyone. I'm fairly sure that he at least experimented with glass plates and new the value of flatness. I'm no AA expert but Ive been lucky enough to have seen his work up really close and read a few of his books.

On any given day Yosemite is but 4 or 5 hours away. But any dream of going there with an 8x10 has pretty much been crushed. I'm still holding out hope that the 4x5 might work.

bglick
1-Jan-2009, 16:47
Rich, I have been very respectful of your posts, and am only trying to offer input based on my experience. If you find any of this offensive, I will immediately stop. On these forums, its difficult to tell when someone takes offense to others opinions. I can assure you Nate meant no harm in his remarks, he has been an avid supporter of this forum and its members for many years.


> For so many to resist (if not hate) the idea of putting magnifying devices in the emulsion plane and then making lp/mm measurements at f-stops known to be the sharpest speaks volumes.


I probably should have expanded on this, as my point was not well received. There is a few different issues at play here:


1) The issue regarding film holder flatness is two fold. First, the flatness of the film holder plate, where the film lies. This needs to be flat to the film holders border, where it makes contact with the view camera back. Second, the view camera back, where it makes contact with the film holder, must also check flat. The addition of a flat granite surface makes this part easy to test. My position is still the same, this is best performed with off-the-shelf straight edges with a .001 or, as high as .0001" dial indicator. The former is more than adequate and can be had for $15 - $100 based on the brand name.



2) Checking resolution at the film plane is a different issue. This is referred to as aerial resolution, AND it can only be checked accurately by another set of optics at the plane. (or it can be reverse calculated with film, more on that below) The most accurate method would be too send the lens off to a optics testing lab, they can give you an entire report on MTF at any f stop, any back focus distance you spec, and MTF data for designated points on the image circle radius. It would be nice if manufacturers provided this info with each lens they produce, but then, it would create "cherry picking" as everyone would want the primo lenses, not the ones which just barely passed the min. performance thresholds. My guess is, these tests would run $150 - $200 per lens....


A home-brew method of doing the same can be accomplished....but with certain caveats. The subject side of the lens should have targets placed at the desired distances. Image magnification must be determined to know which set of targets equate to lp/mm at the film plane. This is best accomplished by using one large target, and measuring it on the gg, now the image scale is set, which you can apply to the test targets.


Now, the hard parts..... assuming you want to use a loupe, the key is to provide a flat surface the loupe can ride on, but be true to the image plane. I once considered doing this.... and my idea was, use a piece of black FLAT acrylic plastic, (low cost and probably flat to .002" at 4x5 size) and draw 4 radius lines from the center outward to each corner....then drill 4 holes on each radius, allow the loupe to view through these holes....you can now take readings at each radius point and record them.


The loupe and the eye are the next obstacles. Lets assume you have good vision and can resolve one arc minute. (mostly younger people < 45 years of age with no vision problems) If you are testing a lens at f8 the max. aerial resolution delivered to the film plane is limited by apt. diffraction at about 188 lp/mm. This is an avg., you can work out the details for all the different wavelengths of light....this is a general discussion to execute the test so the results make sense, as often is the case, the test results demonstrate other weak links in the chain, vs. the variable you were trying to test...... so the tester is fooled.



So what fl loupe is required to resolve 188 lp/mm? There is where many variables come into play. We will work with well accepted conventions here. First, the eyes resolving capability is inversely proportional to viewing distance, i.e. as we double the viewing distance the eye resolves half, and when we half the viewing distance we can resolve 2x. The conventional viewing distance is 250mm / 10". At this distance, here is a well accepted range of resolution of human vision....


2 lp/mm - low end of vision, seniors, low fovea resolution, abberated eye lens, large astigmatisms, etc.

5 lp/mm - VERY good human vision, often <45 years of age, no vision problems.

10 lp/mm - Excellent human vision, often <30 years of age, low abberations in eye lens, high density fovea. (you qualify for Top Gun fighter school)


If a person falls into the first scenario, at 2 lp/mm resolving power at 250mm viewing distance, we must reverse calc. at what viewing distance his eye must be from the image plane to resolve 188 lp/mm. 188/2 = 94. We must reduce the 250mm view distance by 94%, or 6% * 250mm = 15mm. Therefore the eye must be placed 15mm from the image plane for the observer to resolve a 188 lp/mm target at the image plane. So therefore a 15mm magnifier or film loupe is required, at a min. The quality of the loupe comes into play next. If you use a high end loupe, you can often acheive 80%+ MTF value, which is good....however, lower end loupes, can barely hit 50% MTF, making the loupe the limiting factor. In which case, you should halve the fl of the loupe provide better resolving capability (double magnification), in lieu of higher MTF loupes (more expensive) . Lets consider a 7mm fl loupe, which is 36x. (250/7 = 36x) So at f8, your carson loupe is at its limit for this test, and this assumes it has good enough MTF so it does NOT become the limiting factor to test. You can step up to a good astronomy Eye Piece at 7mm fl for about $75 - $100... since you only use the loupe on-axis, any good plossl design EP in the 7mm fl range will suffice.


Next, the eye... a big part of the equation. The MTF and resolution of the eye is HIGHLY dependent on the pupil diameter..... at low pupils ~ 2.5mm the eyes MTF curve (the eye is a lens, it also has MTF curves), shows about 70% MTF, not too bad. But at 4mm diam pupils, the MTF falls to below 25%, very poor, in which case, the eye will be the limiting factor. In other words, to put the eye in "inspection mode" and not allow the eye to be the weak link the optical train, your light source on the target must be ultra bright.... at a bear min. direct sunlight on the target, maybe more, which is dependent on the fstop you are testing the lens at. You need about 15EV to dilate the pupil down to 2.5mm.... you can easily check this at the image plane with a light meter. Anything less than 15EV, your eye will limit what you can resolve and give false readings...


Next, you need the loupe to be on-axis with the lens rays, so a tilting loupe is required.... you may need to jury rig something for this, or have an ultra steady hand... again, another variable... A tilting field microscope would be ideal.


or....... the simpler alternative, which is easier, cheaper and more accurate is....


Once you confirm the camera system is square, flat and gg / film plane are in alignment, you can shoot a piece of film at each f stop, and evaluate the results on a light box or even better, a cheap microscope. Since we know the MTF value of the film at a given contrast (targets), you can simply use 1/R and reverse engineer to find the lens aerial resolutions at each f stop. Thats the beauty of 1/R, the only missing variable in the equation is the aerial resolution of the lens. Careful film processing should be assured to assure the captured resolution is displayed in the processed film. (not a huge variable)

To be sure the film is laying flat, you may consider tilting the camera up a bit, so gravity pulls the film flat. You will have to place the targets higher of course. Of course start with flat film fresh out of the box. This is where a simple vacuum back would be nice.

Both methods will work, but the film version has a LOT less variables to control, hence why it will produce reliable and consistent results as a home brew testing method.


Your next post.... Part II.....

bglick
1-Jan-2009, 17:45
> The non-distorted mirror image is an indication the film is probably flat to +/- .001" or better.

Rich, can you describe what procedure you plan to use to see a perfect mirror image on film? do you shine light on it? BTW, mirrors are way flatter than .001".... but I am confused how you are implementing this mirror technique to check if the film itself is flat???



> after repeatedly snapping in focus across the entire 4x5 frame using aligned glass and
35x loupe.

I mentioned this in previous posts, I don't know if you disagree with me, or you did not read it....but there is NO glass that can resolve the detail the lens will project. Not even close... you are comparing a glass that might resolve 5 lp/mm vs. a lens that is projecting 100 - 300 lp/mm ? The weak link is the first part of your optical chain, agree? My last post explains how you must intercept the rays directly with a second optic right at the image plane, without the aligned glass. Maybe after you read this, you can comment....



> I plead guilty expressing unrealistic hopes and expectations in some instances. Its based on a big investment in a "Universal upgrade to CCD fluid scanning systems"


Unrealistic expectations are what these forums are for :-) Often, there is reality hackers out there, that are ready to help, and....for free....not so bad IMO... What CCD fluid scanning do you refer to? I am currently use a Screen Cezanne Elite which works very well wet mounted up to 5300 dpi... previously, I owned several drums scanners... I find these high flat beds as good as the best drums. The one exception may be the ICG drum scanners, which I have never used... but my guess is, any improvements would be marginal, in the 5% range for both d range and resolution.




> At least not until I can get some really flat focus on some really flat film and determine what the limits are.

I can assure, you, these limits have been well defined for many years. The only addition that testing offers is, just how close your equipment can be to these known limits. Exceeding the limits, it's not in the cards, hence why all this testing, at best, will give you an estimate if you are "at" the limit, or maybe 30% from the limit..... not a huge range, for the amount of work involved. This assumes decent gear, relatively modern lenses, etc. However, the complexity of the tests and all the variables involved can often lead people to believe they re-wrote every optical principle known to mankind :-)



> MAY NOT fit the fervently held canonical belief that only two fstops than can be used for Large Format Photography.


I will assume you are commenting on my previous post. I never stated that only two f stops can be used.... please re read. What I stated was, typically there is ONLY two f stops on LF lenses where the MTF is optimized. You can see this the MTF curves the manufacturers provide. The fall off is dramatic. You can use any f stop you desire, assuming you are not concerned with achieving the max. image quality that lens can is capable of delivering.


Also, remember, its the contrast that is delivered to the film that matters here, not the resolution. Human vision is more sensitive to contrast than pure resolution, specially in the 2 - 5 lp/mm range. So regardless of what is "resolvable", this does not represent the full story behind image quality, hence why MTF has replaced "resolution" as the standard for expressing image quality.... about the mid 1970's, MTF became the standard to express image quality, not resolution, although the two are obviously related. One look at Mamiya 7 color chromes on a light box will make this point ultra clear - a picture is worth a thousand words...



> So if anyone wants to help out please recommend a source of film known to be flat.


How are you confirming all this film is so un-flat? I can't believe I have been this lucky for the past 15 years? I just layed a piece of 8x10 unprocessed Velvia on a Starett 18" square granite stone, certified to +/- .001" flat across its entire surface .... the film lays DEAD flat. In addition, when i insert the film in my Toyo 810 holders, the edges of the film holders are rather taught, stopping the film from buckling from gravity. Can you better explain the problems you are having? And how you determine these problems?



> And if you want to criticize then feel free, but you are expected to support your opinion in the same context as this thread. If you have flat film then post a picture.


I hope you understand, no one is criticizing you. Post a picture of what? Flat film laying a on granite stone? If the film was out .002", could you see this on a picture posted to the web? how? My guess is, you are using this mirror concept, thinking you need 1/8th wave flatness for the film to flat, this is NOT the case.... but maybe I am not understanding you.... so i await...




> The use of DOF to describe Depth of Focus and/or Depth of Field is obfuscation at its worse for some of us who do not have "i know the context" built into our DNA especially when they get intermixed (sigh).


Rich, these forums are for people to share ideas and to help each other. In this case, I have pointed you in the right direction, and spent too much time already on these posts, as these subjects are not easy to explain clearly in a few sentences. However, I can not spend days putting together tutorials to teach these subjects in detail. Read some photo optics books, check Amazon, they have MANY of them, all for different levels....they contain the graphics, math, and explanations that you need to fully understand the principles which you are addressing in this thread. I can assure you, once you have a better understanding of the optics, your positions on these subject matters will change.




> I feel like an idiot for even making two 8x10 plenums and prototyping the corner stand. I honestly wondered if AA used this technique and did not tell anyone. I'm fairly sure that he at least experimented with glass plates and new the value of flatness.


You should never feel like an idiot for experimenting with any of this Rich, I totally respect your tenacity... which is part of the reason I have worked so hard to explain all this in such detail.. it's all part of the learning experience.


As for AA.... I sincerely doubt he did any of what you suggest, mainly because, it simply is not necessary. What AA understood well was that long fl lens (required on 810 format) had very little DOF....or when high DOF was used, it would dramaticaly reduce resolution. (DOF = Depth of Field, Depth of Focus is spelled out to prevent confusion). So to max. OFR, he understood it was important to push the near subjects far from the lens. This was a secret style he kept hush for years, i think he started it in the late 50's or 60's.... he used to mount his 8x10 on 15 ft high ladders to push the nears out, so the image would produce tremendous sharpness at f32. In his later years, he shot atop his motorhome. I copied this method for many of my 810 shots, its very effective, as you are almost taking an infinity shot, which maximizes the recorded resolution, as you can often shoot at f22 or 32 vs. f64. Its this resolution, whereas the big format differentiates from the smaller formats. It all comes down to a better understandings of the optics math. OFR is a function of aerial resolution which is dictated by apt. diffraction, combined with the MTF of the film used. Since AA shot almost all B&W in 810, it's no coincidence (or magic) his images are deemed utlra sharp, even by todays standards, specially considering the small prints he often makes. In my world, I print up to 10 ft long, so I consider AA prints small, its all relative.


Of course, many on this forum are just as capable of producing the same (or better) today, specially due to better lenses and better films, and much more precise printing methods that offer better tonality, digital sharpening, larger color gamuts, etc. etc. The point being, AA's success was not due to ultra high precision gg / film alignment - to better than +/- .001". Depth of Focus took care of this.... Instead, he learned the value of lower f stops to maximize OFR, which is why many of his shots do not have near subjects.

.

rvhalejr
1-Jan-2009, 19:02
Not that long ago, I exchanged info on line with a guy who made a DIY 4x5 vacuum holder. It didn't look that hard to do. It turns out that a rubber bulb pipette bulb has enough suction. I no longer have the contact info, but a little Googling should turn it up.

I really want to get the 4x5 sharpness I'm seeing onto film. Thats with a Depth of Field of 10ft, 40ft and 300ft.

Its with the 4x5 clear plenum calibrated to a .190" critical dimension at f22 with a
Schneider-Kreuznach Angulon 1:68/90 S/N 5415433 restored Hollywood ready 1949
Speed Graphic. Whats even more of a surprise is that its holding almost the same sharpness into the corners, this from the most inexpensive WA German lenses I
have and my budget is been about zero for the last year.

Anyway, to remove flatness as a variable I'm going to have to try the V-Back again. All I need to see are holes that do not rumple the film as its sucked flat over the hole. I'm going to try .050" and then maybe .020" but I may not be able to get much smaller than that.

As the diameter gets smaller the number of holes along the edge may need to increase. My last attempt at .125" and 100 holes per holder failed (as mentioned
before due to rumpling or distorting the image). I'm hoping that the density on the smaller holes will not go up much as it would take forever to drill and hone 200 holes, 400 would be a month long project.

My roll and tape method progressed but I've seen nothing of the USB IR camera on
order and do not have the time to fuss with one trying in hopes of removing the IR filter (to roll and tape unexposed film in darkness). Then there is the matter of routing a precision .030" channel in the holder for the bigger septum to slip into.

I do have a set of four holders (eight septums at .192 or .193) but have not
been able to find film that is +/- .001 out of the box to match (not that it even
ever existed except for glass plate). I've posted pictures of out-of-the box
curled film and the distorted image from the refection off the un-exposed
4x5 velvia emulsion, outside with full sun in my face and captured by an old Nikon DSLR f8 1/25 ISO 2000 with gamma amplified in photoshop to about 4 so as
everyone can see the mirror like distorted reflection.

I also shot a rolled and taped mounted (perfectly flat like is done for a fluid
drum scan) with a perfect mirror like reflection.

The Proof for Mirror Like Reflection Flatness
Skip this unless you really got to know
I've been using the mirror like reflection as a standard of near-perfect flatness,
no tools or measurement needed if the following is true. Window Glass is usually flat to .001" so it works fine. If I stick a .0015 feeler gauge shim behind the film and roll over it I can see the distortion in the reflection on the film. If I stick a finger-nail flattened piece of common household aluminum foil underneath the film and roll over it I can really can not make out any distortion in the film emulsion reflection with the unaided eye. Since Flattened Aluminum foil is consistently .0005" and the smallest automotive feeler gauge .0015" it is likely that film flatness is between the two values, .001" which is (for my purposes) perfectly flat in a carefully engineered
metrology context (or at least reasonable approximation). It also helps that
whichever way I measure my batch of velvia it comes out to be .0095" thick.
End of really detailed information

All the photographer needs to know is if you can get a mirror like reflection
(no distortion) off the emulsion of a piece of film then its plenty flat.

I've got an excess of out-of-the-box curled junk so if I bought more I'd want to send it back if it was curled as well (and no-one will want to do that).

All the Best,

Richard

rvhalejr
2-Jan-2009, 00:40
Rich, I have been very respectful of your posts, and am only trying to offer input based on my experience. If you find any of this offensive, I will immediately stop. On these forums, its difficult to tell when someone takes offense to others opinions. I can assure you Nate meant no harm in his remarks, he has been an avid supporter of this forum and its members for many years.


The value of what you all are writings is worth far more than what I am able to contribute. My mission (to obtain the best results from what often turns out to be marginal equipment) would be better served in another thread created for the purpose of a structured discussion and planning, procedural documentation, execution and analysis of results. Predictive models and experience are useful, but not at the expense of validation testing. My goal is to obtain the best possible image using tools that make up a simple kit. The 35x Loupe may not be ideal but even it scares a lot of photographers and is far more powerful than the conventional (up to 10x maybe). The 100x with reticule is overkill, but tends to settle a good deal uncertainty when needed. The 400x microscope will remain in the closet as I took and published my last set of micro photographs (of racking through emulsion layers) a long time ago.



> For so many to resist (if not hate) the idea of putting magnifying devices in the emulsion plane and then making lp/mm measurements at f-stops known to be the sharpest speaks volumes.

I probably should have expanded on this, as my point was not well received. There is a few different issues at play here:

1) The issue regarding film holder flatness is two fold. First, the flatness of the film holder plate, where the film lies. This needs to be flat to the film holders border, where it makes contact with the view camera back. Second, the view camera back, where it makes contact with the film holder, must also check flat. The addition of a flat granite surface makes this part easy to test. My position is still the same, this is best performed with off-the-shelf straight edges with a .001 or, as high as .0001" dial indicator. The former is more than adequate and can be had for $15 - $100 based on the brand name.


My wife would kill me if she saw the surface plate. An off-the-shelf straight edge
is part of the kit, as are glass gauge blocks, a feeler gauge and glass plenum (that can substitute as a surface plate as its flat to within about .001" . As an option Digital Calipers can be added, honed and with the .0005" touch feature.

From a metrology perspective your setup is superior to mine (in a lab calibration
context) but I do have a lot of high precision machine shop experience (prior to
going back to school) and believe we both have identified the important datums
that most mechanical engineers would want us to pay attention to.

I have some sketches and pictures of this process but might need to add more
to be sure all the bases are covered. From what I've seen the Stainless Steal
Straight edge, gauge block and feeler gauge are accurate enough. Admittedly
the dial indicator on the gauge block is easier than a feeler gauge. But my wife
would divorce me as as the dial indicator and surface plate would make my garage
into a complete machine shop (and she does know what one looks like).

It would not hurt to compare both (I would need to be really stealthy about it)
but go-nogo gauging and .0005" touch are probably good enough for this old
inspector.



2) Checking resolution at the film plane is a different issue. This is referred to as aerial resolution, AND it can only be checked accurately by another set of optics at the plane. (or it can be reverse calculated with film, more on that below) The most accurate method would be too send the lens off to a optics testing lab, they can give you an entire report on MTF at any f stop, any back focus distance you spec, and MTF data for designated points on the image circle radius. It would be nice if manufacturers provided this info with each lens they produce, but then, it would create "cherry picking" as everyone would want the primo lenses, not the ones which just barely passed the min. performance thresholds. My guess is, these tests would run $150 - $200 per lens....


A home-brew method of doing the same can be accomplished....but with certain caveats. The subject side of the lens should have targets placed at the desired distances. Image magnification must be determined to know which set of targets equate to lp/mm at the film plane. This is best accomplished by using one large target, and measuring it on the gg, now the image scale is set, which you can apply to the test targets.


Now, the hard parts..... assuming you want to use a loupe, the key is to provide a flat surface the loupe can ride on, but be true to the image plane. I once considered doing this.... and my idea was, use a piece of black FLAT acrylic plastic, (low cost and probably flat to .002" at 4x5 size) and draw 4 radius lines from the center outward to each corner....then drill 4 holes on each radius, allow the loupe to view through these holes....you can now take readings at each radius point and record them.


The loupe and the eye are the next obstacles. Lets assume you have good vision and can resolve one arc minute. (mostly younger people < 45 years of age with no vision problems) If you are testing a lens at f8 the max. aerial resolution delivered to the film plane is limited by apt. diffraction at about 188 lp/mm. This is an avg., you can work out the details for all the different wavelengths of light....this is a general discussion to execute the test so the results make sense, as often is the case, the test results demonstrate other weak links in the chain, vs. the variable you were trying to test...... so the tester is fooled.

So what fl loupe is required to resolve 188 lp/mm? There is where many variables come into play. We will work with well accepted conventions here. First, the eyes resolving capability is inversely proportional to viewing distance, i.e. as we double the viewing distance the eye resolves half, and when we half the viewing distance we can resolve 2x. The conventional viewing distance is 250mm / 10". At this distance, here is a well accepted range of resolution of human vision....


2 lp/mm - low end of vision, seniors, low fovea resolution, abberated eye lens, large astigmatisms, etc.

5 lp/mm - VERY good human vision, often <45 years of age, no vision problems.

10 lp/mm - Excellent human vision, often <30 years of age, low abberations in eye lens, high density fovea. (you qualify for Top Gun fighter school)


If a person falls into the first scenario, at 2 lp/mm resolving power at 250mm viewing distance, we must reverse calc. at what viewing distance his eye must be from the image plane to resolve 188 lp/mm. 188/2 = 94. We must reduce the 250mm view distance by 94&#37;, or 6% * 250mm = 15mm. Therefore the eye must be placed 15mm from the image plane for the observer to resolve a 188 lp/mm target at the image plane. So therefore a 15mm magnifier or film loupe is required, at a min. The quality of the loupe comes into play next. If you use a high end loupe, you can often acheive 80%+ MTF value, which is good....however, lower end loupes, can barely hit 50% MTF, making the loupe the limiting factor. In which case, you should halve the fl of the loupe provide better resolving capability (double magnification), in lieu of higher MTF loupes (more expensive) . Lets consider a 7mm fl loupe, which is 36x. (250/7 = 36x) So at f8, your carson loupe is at its limit for this test, and this assumes it has good enough MTF so it does NOT become the limiting factor to test. You can step up to a good astronomy Eye Piece at 7mm fl for about $75 - $100... since you only use the loupe on-axis, any good plossl design EP in the 7mm fl range will suffice.


Next, the eye... a big part of the equation. The MTF and resolution of the eye is HIGHLY dependent on the pupil diameter..... at low pupils ~ 2.5mm the eyes MTF curve (the eye is a lens, it also has MTF curves), shows about 70% MTF, not too bad. But at 4mm diam pupils, the MTF falls to below 25%, very poor, in which case, the eye will be the limiting factor. In other words, to put the eye in "inspection mode" and not allow the eye to be the weak link the optical train, your light source on the target must be ultra bright.... at a bear min. direct sunlight on the target, maybe more, which is dependent on the fstop you are testing the lens at. You need about 15EV to dilate the pupil down to 2.5mm.... you can easily check this at the image plane with a light meter. Anything less than 15EV, your eye will limit what you can resolve and give false readings...


Next, you need the loupe to be on-axis with the lens rays, so a tilting loupe is required.... you may need to jury rig something for this, or have an ultra steady hand... again, another variable...

A tilting field microscope would be ideal.


Continued in subsequent post (we ran out of room).

rvhalejr
2-Jan-2009, 00:46
Continued from previous post

I've fabricated and tested the angled stands for the 35X and they cover the
entire 4x5 frame. Could probably come up with something similar for the 100x.
Take a little practice but its very solid, no rock, but it ain't easy, it can blow
up during machining and about half get tossed (50% yield) There a a lot of
angles to those things and a good deal of honing so that there is no rocking.



or....... the simpler alternative, which is easier, cheaper and more accurate is....

Once you confirm the camera system is square, flat and gg / film plane are in alignment, you can shoot a piece of film at each f stop, and evaluate the results on a light box or even better, a cheap microscope. Since we know the MTF value of the film at a given contrast (targets), you can simply use 1/R and reverse engineer to find the lens aerial resolutions at each f stop. Thats the beauty of 1/R, the only missing variable in the equation is the aerial resolution of the lens. Careful film processing should be assured to assure the captured resolution is displayed in the processed film. (not a huge variable)

To be sure the film is laying flat, you may consider tilting the camera up a bit, so gravity pulls the film flat. You will have to place the targets higher of course. Of course start with flat film fresh out of the box.

This is where a simple vacuum back would be nice.

I've resigned my self to trying that again (ugh).

A regular holder can work if the film is not curled. But unless some turns up that looks
like a mirror (turn on an overhead photo light and sweep the reflected emulsion image
back and forth until the entire piece of film as been examined, if it is all mirror like its
flat, if there is distortion it is not). Deforming the film with .0005" shim and .0015"
feeler gauge tells us the the lowest level of out-of-flat distortion is between the
two at .001" which for our first approximation should be acceptabe.




Both methods will work, but the film version has a LOT less variables to control, hence why it will produce reliable and consistent results as a home brew testing method.


Your next post.... Part II.....

Nathan Potter
2-Jan-2009, 08:50
A few more comments and questions:

rvhalejr, when I was doing IC chip photography in an industrial environment I was after a degree of precision similar to what you are after. I used an optical bench for stability and tilting stages for the standards so could align the standards exactly parallel. Prior to obtaining a vacuum holder for the film I would use a grease to keep the film flat - If I remember it was an Apiezon product - very messy but did the job. It was removed using a solvent (AR xylene) with the film resting on clean room wipes. All messy to do in the dark.

Yes the vacuum holder is a bear to machine and as you describe your efforts I think 0.125 dia. holes are too large given the weak modulus of 6 or 8 mil polyester film. The holes I used were about 0.025 diameter. Since air continually leaks in slightly from around the film edge one needs a continuous vacuum draw. Also the plenum (as you call it) of the holder I made of stress relieved aluminum so that after precision surface grinding warpage would be minimized. The entire holder was machined from aluminum and was compatible with a standard dark slide. A dummy holder could take a ground glass or clear glass for focusing purposes. The stage for focusing was micrometer driven the barrels calibrated in 0.0001 units (2.5um) so extremely fine focus control was possible. Maybe some of these comments will be of help to you.

Two other factors come to mind, now that you and bglick have me thinking about such degrees of precision.

In the case of a monorail camera for example, the Thermal Expansion Coefficient (TCE) of the rail may be relevant. Aluminum runs about 20X10^-6 so the rail can be expected to change length say .002 inch per 10 degrees C for a 10 inch distance between front and rear standards. So for your desired degree of precision you want to have the setup reasonable temperature stabilized.

Another operational factor is the use of the focusing aid. When placed against the GG the rear standard moves forward slightly (depending on the stability of the camera) confounding the exact focus spot. Even my admittedly rugged Technikardan moved at the top up to .007 inch using a feeler gauge and 2 oz. force using a dynamometer. Made a quick check last nite.

Yet another issue I know nothing about has to do with the degree of flatness of field for modern lenses. I would have a hunch that even the best lenses don't have a field flatness for best point of focus that is within 0.010 inch but I don't really know.

Well, just a few more issues to add to the pot.

Nate Potter, Austin TX.

bglick
2-Jan-2009, 09:51
> Predictive models and experience are useful, but not at the expense of validation testing.


This purpose of bringing forth "known" optical principles, is to fine tune the real world testing, so the test, and the results makes sense... and you don't trick yourself with the results. That was my purpose, though it failed miserably. My only final comment on your posts.... your concept of film producing a mirror image has no basis. Film is NOT a mirror, it does not have a uniform reflective surface, its composed of different layers and my guess is, light will reflect off any part of the film NOT just the surface...you are treating film as a first surface mirror, which it is NOT!


> I would have a hunch that even the best lenses don't have a field flatness for best point of focus that is within 0.010 inch but I don't really know.

Good point.... lenses themselves are not held to tolerances this great, at least for LF... the standard can be square, but not the lens panel, and then, all angular errors at the lens panel are exaggerated linearly by distance to the film plane. This is why all this precision is absolute senseless for LF photography.


But more importantly, if the OP read a good optics book, that clearly illustrates Depth of Focus at the film plane, he would comprehend why .001" alignment goals at the film plane will provide no benefits. This is why LF lenses are optimized for f22+ (except a few of the SWA lenses). Its all about Depth of Focus.

However, I am not discounting the need to check alignment on old view cameras, as they can be out .3" without the user even knowing it, and that would represent a very serious error with obvious image degradation.

bglick
2-Jan-2009, 10:51
Nate, the lens panel itself represents a bigger issue than previously thought. The reason is, up till now, we have been discussing flatness on a single plane. A lens board requires co-planar flatness, as the front of the panel supports the lens, the rear side makes contact with the front standard. Co-planar flatness is the hardest of all to achieve, as its not a single milling operation. To hold .001" (or better) thickness tolerance on a lens panel is entering NASA type specs, with only the highest precision mills and machinist can achieve. I can assure you the $150 for high end lens panels we buy are not milled to this level of precision.

The point of mentioning this is..... Angular errors at the lens panel, will double at the film plane each time the focal distance doubles... this is beyond our scope for correcting....... hence the Depth Of Focus gift - which makes LF photography possible.

As for the lens tolerances you mentioned.... an interesting story. I deal with the Schneider factory in Germany a lot, for specialty cameras I build. About 4 years ago, I start using a lot of Digitar lenses. One lens had a defective Copal shutter. I asked the factory if I could replace it with some other new Copal 0 shutters I had on hand. The response was - NO! You must send the lens back to Germany.

The reason is..... to produce the advertised MTF, and hold the film image plane flat to the digital sensor, the front and rear elements must held "near" perfectly square, and therefore must be shimmed with accuracies well below .001".... a laser is used through the lens front, and the projected points are measured till they meet a min. requirement. Then, the shims are permantely secured. That shutters serial number is dedicated to THAT single Digitar lens. Anyway, this demonstrates how the errors that enlarge (due to distance) are the errors that require the most precision to control. Well beyond the home-brew measures this thread is addressing. Not to mention, each lens and lens/panel will have its own slight errors which are never consistent, hence why alignment down to .001" between the image plane and film plane is impossible for a camera system that used many film holders and many lenses / lens panels.


But of course, these Digitar lenses are optimized at f5.6, not f32, so it's a completely different animal vs. LF film photography. Depth of Focus works against the digital user, and works in favor of the LF film user.... Kudos to the virtues of BIG film !!!

rvhalejr
2-Jan-2009, 14:18
> The non-distorted mirror image is an indication the film is probably flat to +/- .001" or better.

Rich, can you describe what procedure you plan to use to see a perfect mirror image on film? do you shine light on it? BTW, mirrors are way flatter than .001".... but I am confused how you are implementing this mirror technique to check if the film itself is flat???

Here are some images, Note that I had to face and shoot into full sunlight with the DSLR. No significant light penetrates the film, its not back light. This is all reflection off the undeveloped out-of-box film emulsion. Focusing on the emulsion is very difficult. You set up AF on spot and aim for one of those airy disk like dots on the reflected image plane.

This is how to document, but not how I envision it. The photographer would use emulsion reflection to check their mirror like roll and tape job for flat bed scanning (borrowed from the old tango fluid mount technique). Any really out-of-the-box flat film in a film holder when held under a photo lamp or chandelier will have an emulsion reflection very to that here, which is similar to a hand mirror and easily detected by the naked eye once you have trained yourself to do so.

When the film is not flat we get a "circus-mirror" effect (some will recognize that phrase from NK so don't rat me out or he may get on me again - which is ok, anything for photography, I mean science).

Since to material I get for plenums is flat to about .001" (there can be up to that much variance in thickness) and the simple go-nogo qualification test, the smallest distortion detectable by my old rebuilt eyes appear to be between .0005" and .0015" according to the instructions that fallow.

The detection procedure was to place a shim between the film and glass table top (poor mans surface plate and/or husband with way to many tools and camera gear) and roll over it, firmly, (with a rubber roller or 2" piece of PVC pipe). .0005" will not deform the film but the .0015" shim seems to.

Like mounting film on a drum scanner press to lightly and it will not go flat, press to hard and you'll put ripples in the emulsion, even with another piece of film or optically clear acetate on top for protection.



> after repeatedly snapping in focus across the entire 4x5 frame using aligned glass and 35x loupe.

I mentioned this in previous posts, I don't know if you disagree with me, or you did not read it....but there is NO glass that can resolve the detail the lens will project. Not even close... you are comparing a glass that might resolve 5 lp/mm vs. a lens that is projecting 100 - 300 lp/mm ? The weak link is the first part of your optical chain, agree? My last post explains how you must intercept the rays directly with a second optic right at the image plane, without the aligned glass. Maybe after you read this, you can comment....


Theoretically you are the best, Experimentally you appear to be reticent, so let me try to bring you up to speed. A while back I wondered if there would be any use for a pocket microscope on the GG to help with focusing (since they have become so affordable now). I thought (being au unusually clever experimentalist) that his could potentially be fertile ground (much earlier I had put a microscope in the emulsion plane and knew that it could work) to investigate.

When I finally got the right pocket microscope (Lots of helical Adjustment because I knew there was at least ONE INCH OF DEPTH OF FOCUS to deal with). I stuck it on my old Ultra-brite fresnel GG and was disappointed. It was obvious the GG had to go, so I pulled it off (leaving the back register ready to accept whatever I could find.

SO... I grabbed some CDs (ya know they fit in the Film holder slot PERFECTLY) with HOLES IN THE MIDDLE so there would be nothing between the film plane image and pocket microscope. Four CDs stacked on each other put the stand of the 35x Micro... OPPS!!! I mean Loupe stand right almost right on the film plane.

I had a whopping bunch of helical adjustment (to move the loupe forwards and backwards along the film plane's NORMAL VECTOR. What I saw snap into focus at almost a point floored me (90mm Schneider Angulon at f22).

Thats a first rough approximation, and the point of best focus cannot really be a point and must have a small range, as any Microscopist OOOPs !! I mean loupe fine focuser should know. I'd set the eyepiece helical adjustment in the middle (as it only turns 1 revolution in either direction and travels about .125" total). Then tweak it at the eyepiece. Then go back and tweak the camera rack (and pinion) OOOOOOhhhhhhhh AAAAAAHHHHhhhhhhh look at that airy disk .,.

The 100x with reticule is really painful to use, its good for checking lp width and
distance, and even the size on an airy disk (which I have not done but have recently posted a table of values the vary by f-stop). The 35X microscope probably needs to be characterized in terms of 1/R that make sense, etc.

So I've concluded that a 400X microscope with stand is the probably capable of measuring the lp/mm metric of any lens made (so far and as CS mentions in his manuscript and I experimentally verified). The 100x is for those of us that need assurance the lens we just bought and sold meets expectation (and its characteristic profile can be certified to). The 35-40x Loupes good for everyday AA wannabe photographers with old reconditioned (undergone optical surgery) eyeballs. And with a little help from our friends (hats off to bglick) we might just get a chance to have a religious behind the lens of our big cameras at Yosemite (or where ever we happen to have good subjects and good light).



> I plead guilty expressing unrealistic hopes and expectations in some instances. Its based on a big investment in a "Universal upgrade to CCD fluid scanning systems"

Unrealistic expectations are what these forums are for :-) Often, there is reality hackers out there, that are ready to help, and....for free....not so bad IMO... What CCD fluid scanning do you refer to? I am currently use a Screen Cezanne Elite which works very well wet mounted up to 5300 dpi... previously, I owned several drums scanners... I find these high flat beds as good as the best drums. The one exception may be the ICG drum scanners, which I have never used... but my guess is, any improvements would be marginal, in the 5% range for both d range and resolution.


I think I just had a religious experience over your scanner, OOOOOhhhhh, AAAAHHHHhhhhh !!! :^)




> At least not until I can get some really flat focus on some really flat film and determine what the limits are.

I can assure, you, these limits have been well defined for many years. The only addition that testing offers is, just how close your equipment can be to these known limits. Exceeding the limits, it's not in the cards, hence why all this testing, at best, will give you an estimate if you are "at" the limit, or maybe 30% from the limit..... not a huge range, for the amount of work involved. This assumes decent gear, relatively modern lenses, etc. However, the complexity of the tests and all the variables involved can often lead people to believe they re-wrote every optical principle known to mankind :-)



If I may be so bold to suggest that this may arguably be similar to the classical differences between the theorist and experimentalist, not that you (nor I or any engineer/scientist for that matter) cannot wear both hats. I'm old so here comes another story to illustrate .,.

Once upon a time I worked with rocket scientists (ref the HST post). After having to many glasses of wine at lunch I saw a little gray humanoid with a 10 gallon hat and overheard gray talking to a group of Senior Scientists, but his mouth was not moving. They were just another group visiting from the area 51 facility.

Now, many often point to this anecdotal story and explain, all of our technology came
from crashed alien space ships !


Running out of space, continued in subsequent post .,.

rvhalejr
2-Jan-2009, 15:30
Continued from previous post .,.

The problem is all of our technology comes from paper after published paper, each
one building on the previous work and incrementally bringing us closer to the ever elusive final approximation. I'm sure that all the technology in, for instance, stealth aircraft comes from a pile of incrementally publish papers if stacked on top of each other would reach over one hundred feet high.

No where in that stack is there a giant leap in science and technology that could have come from anywhere but a lot of dedicated researchers and developers spending their entire professional life trying to incrementally improve the understanding and utility of their discipline.

I have not done this with optics (yet) but there are disciples in which I have exhaustively read and researched papers and patents, I recommend that to anyone who believes that a giant leap due to one person (or aliens for that matter) is possible.

What ever our findings are they will conform to well accepted optical theory and convention. The only thing that has changed is the common availability of a more powerful optical tool (pocket microscope/loupe). In theory it removes more uncertainty from the process of conformal focusing (like my old eye balls).

In another life I characterized the energy profile of 10MeV photon accelerator beams for a group of board licensed medical physicists based on conventional mathematical models and theory. It did create a stir but it was due to a small incremental improvement in visualization as a result of lot of hard work and hand wringing on my part (nothing like sticking ones neck out for the possibility on an incremental advancement.

A wise man once told me at some point you will need to run it up the flag pole and they will either shoot at it or salute.

My characterization of photon scatter (presumably the enemy of resolution) starts with the rate of change at a point, then change the rate of change (second derivative) and so on. Math is not my strong suit.

But somehow, after looking at the data, and reconciliation with generally accepted mathematical theory, the project can be neatly summarized and perhaps provide some small incremental improvement to those interested in the discipline.

Continued in subsequent post .,.

Nathan Potter
2-Jan-2009, 16:02
Huh, Phew! Richard you seem to be drifting into never/never land. I think you were on track with your original objective so you need to beam back down on an electromagnetic wave - Maxwell can show you how. Keep experimenting even with primitive tools; it's good for the mind.

Nate Potter, Austin TX.

rvhalejr
2-Jan-2009, 16:50
Continued from previous post .,.

(I lost a post in here somewhere, I will try to recover for some semblance of continuity of thought .,. )



> MAY NOT fit the fervently held canonical belief that only two fstops than can be used for Large Format Photography.

I will assume you are commenting on my previous post. I never stated that only two f stops can be used.... please re read. What I stated was, typically there is ONLY two f stops on LF lenses where the MTF is optimized. You can see this the MTF curves the manufacturers provide. The fall off is dramatic. You can use any f stop you desire, assuming you are not concerned with achieving the max. image quality that lens can is capable of delivering.


I am concerned about the max lp/mm a lens can deliver, on 45 thats usually a couple off stops and according the legendry site for lp/mm lens characterizations you cited in a previous post the lens I'm using is likely the most sharpest between +f16, f22 and -f32 which is an interval best described as a function of probabilistic distribution i.e. the two stops the lens was designed and manufactured for.



Also, remember, its the contrast that is delivered to the film that matters here, not the resolution. Human vision is more sensitive to contrast than pure resolution, specially in the 2 - 5 lp/mm range. So regardless of what is "resolvable", this does not represent the full story behind image quality, hence why MTF has replaced "resolution" as the standard for expressing image quality.... about the mid 1970's, MTF became the standard to express image quality, not resolution, although the two are obviously related. One look at Mamiya 7 color chromes on a light box will make this point ultra clear - a picture is worth a thousand words...


Tonality, (Contrast) and references to the zone system is a another body of work for me (more than worthy of future discussion)... :) ...I've had a couple of Mamiyas, good to hear they finally got it right. Don't get me started on 645, 66, 67, 69, 612, etc. or the love will come gushing out. Lets save that one for a rainy day.:D

I'm very comfortable evaluating optical systems (in my tiny little way) OR films at their near theoretical limit exclusive of each other. Throwing film in the mix scares me, but I know eventually I'll have to go there. I just wanted it as flat at exposure as it will be at scan time (to keep variables in the work flow on a level playing field). I've been hoping (erring on the side on conservatism) that .001" would be a SAFE place to start
(wait for it at the end).

Having said that I need a high altitude examination of all the documentation (at some
point) and decide what are the best places to bring in 1/r equations. Since I've used
CS's manuscript as a starting point, and it does start out with empirical 1/r it will be included ideally at some appropriate point.

It's probably poor etiquette that I have not cited it up front because one might conclude (reasonably) that the phrase "Fine Focusing and Calibration" should not be used without 1/r being cited immediately, otherwise the author/poster would be overlooking (what appears to be) the most important fundamental of the discipline.

Very poor form :o OUCH !!!



> So if anyone wants to help out please recommend a source of film known to be flat.

How are you confirming all this film is so un-flat? I can't believe I have been this lucky for the past 15 years? I just layed a piece of 8x10 unprocessed Velvia on a Starett 18" square granite stone, certified to +/- .001" flat across its entire surface .... the film lays DEAD flat. In addition, when i insert the film in my Toyo 810 holders, the edges of the film holders are rather taught, stopping the film from buckling from gravity. Can you better explain the problems you are having? And how you determine these problems?


In light of the four images (two of flat and two of out-of-flat film) and other details revealed I'm going to assume your very reasonable questions are in the process of being drawing us closer to a consensus.

I'm now going to attach an example of 4x5 velvia that exhibits the horns of film curl from hell, out-o-the-box (a freshly opened pack). Hey, its a piece now, "The HORNS of HELL" one of my really artsy (sic considering all the pain) photos.



> And if you want to criticize then feel free, but you are expected to support your opinion in the same context as this thread. If you have flat film then post a picture.

I hope you understand, no one is criticizing you. Post a picture of what? Flat film laying a on granite stone? If the film was out .002", could you see this on a picture posted to the web? how? My guess is, you are using this mirror concept, thinking you need 1/8th wave flatness for the film to flat, this is NOT the case.... but maybe I am not understanding you.... so i await...


The new information in the thread-up date (four in the previous post and the soon to be infamous "The HORNS of HELL" piece) may help bring us closer to a consensus.

I HATE going off topic (I'm probably a worse Offending Poster {OP?} than everyone else) but optical flats and newtons rings are a discussion I'm looking forward to at some future time (and re-visting the latest electronic flatness probes, etc.)

At this point I'm hoping to attain the best possible alignment within a reasonable probability. There is more to this than should be described here, so please wait until the end of this sub-thread before investing your valuable time in a reply (I tremble
at the thought of your bill rate).



> The use of DOF to describe Depth of Focus and/or Depth of Field is obfuscation at its worse for some of us who do not have "i know the context" built into our DNA especially when they get intermixed (sigh).

Rich, these forums are for people to share ideas and to help each other. In this case, I have pointed you in the right direction, and spent too much time already on these posts, as these subjects are not easy to explain clearly in a few sentences. However, I can not spend days putting together tutorials to teach these subjects in detail. Read some photo optics books, check Amazon, they have MANY of them, all for different levels....they contain the graphics, math, and explanations that you need to fully understand the principles which you are addressing in this thread. I can assure you, once you have a better understanding of the optics, your positions on these subject matters will change.


A better understanding of optical system theory will definitely be helpful. I think our positions are that far off now and that difference is probably more a function of me not giving you all the details (like the images attached) or just not communicating well enough (writing can be hard) and flat out ignorance of LF protocol (I had an earlier
mishap with movements a while back) I think the end of this sub-thread will bring us closer.




> I feel like an idiot for even making two 8x10 plenums and prototyping the corner stand. I honestly wondered if AA used this technique and did not tell anyone. I'm fairly sure that he at least experimented with glass plates and new the value of flatness.

You should never feel like an idiot for experimenting with any of this Rich, I totally respect your tenacity... which is part of the reason I have worked so hard to explain all this in such detail.. it's all part of the learning experience.

As for AA.... I sincerely doubt he did any of what you suggest, mainly because, it simply is not necessary. What AA understood well was that long fl lens (required on 810 format) had very little DOF....or when high DOF was used, it would dramaticaly reduce resolution. (DOF = Depth of Field, Depth of Focus is spelled out to prevent confusion). So to max. OFR, he understood it was important to push the near subjects far from the lens. This was a secret style he kept hush for years, i think he started it in the late 50's or 60's.... he used to mount his 8x10 on 15 ft high ladders to push the nears out, so the image would produce tremendous sharpness at f32. In his later years, he shot atop his motorhome. I copied this method for many of my 810 shots, its very effective, as you are almost taking an infinity shot, which maximizes the recorded resolution, as you can often shoot at f22 or 32 vs. f64. Its this resolution, whereas the big format differentiates from the smaller formats. It all comes down to a better understandings of the optics math. OFR is a function of aerial resolution which is dictated by apt. diffraction, combined with the MTF of the film used. Since AA shot almost all B&W in 810, it's no coincidence (or magic) his images are deemed utlra sharp, even by todays standards, specially considering the small prints he often makes. In my world, I print up to 10 ft long, so I consider AA prints small, its all relative.


WOW ! What wonderful insight you have. What you have described really amazes me.

At a later time I would like to discuss this one movement, which to implement correctly requires raising the front lens up (I'll post a picture) but to do that on a 4x5 the lens must be capable of covering 8x10 if significant fall off is to be avoided. This is the LF Architectural Technique I'd go for instead of trying to get on top of a trailer. Not quite the spatial orientation of that you describe but maybe good enough for a LF Yosemite Picture taking wanna-be (the pdf on LF Rise is two pages).

Continues in next post

rvhalejr
2-Jan-2009, 17:21
Continued from previous post



Of course, many on this forum are just as capable of producing the same (or better) today, specially due to better lenses and better films, and much more precise printing methods that offer better tonality, digital sharpening, larger color gamuts, etc. etc. The point being, AA's success was not due to ultra high precision gg / film alignment - to better than +/- .001". Depth of Focus took care of this.... Instead, he learned the value of lower f stops to maximize OFR, which is why many of his shots do not have near subjects.
.

And so it is. I want to exploit f stops with the best OFR which may not be the same as the best lp/mm . I think the best thing for me is get the best precision gg / film alignment within reason, and then make sure the Depth of Focus is adequate to encompass the emulsion layer.

The 35x Eyepiece can move at least a half turn without affecting focus noticeably, a distance along the film plane normal vector of about .030" inch == +/- .015" which a photography guru once told be was a good thing. I need to verify that this is truly Depth of Focus and not just a characteristic of the 35x optic (which at this point I doubt).

The Sinar post (attached) demonstrates that (in some instances) a variance of .012" is not good.

Some of my best customers are Sinar owners (known for really flat film holders, etc.)
so I use the 4x is better and safer rule; .012/4 == .003" should be good in just about any circumstances.

I initially went for .001" (and may get it) but there is a good probably some systems will end up at .002". I'm saving .003" as a margin of safety, Iv'e dropped a glass plenum before (what a dangerous mess) and have also done that to film holders (there goes the alignment).

Whats FANTASTIC about this is that the acrylic plenums do not break, but their thickness can vary by about .003" (or a little worse even) so thats great because its acceptable (if I've finally got it right about Depth of Focus). Same goes for film holders.

Now if I could just get Ready Loads or Quick Loads or even sheet film that doesn't look like a circus mirror .,.

rvhalejr
2-Jan-2009, 17:27
Huh, Phew! Richard you seem to be drifting into never/never land. I think you were on track with your original objective so you need to beam back down on an electromagnetic wave - Maxwell can show you how. Keep experimenting even with primitive tools; it's good for the mind.

Nate Potter, Austin TX.

Thanks Nate,

The bglick reply is complete with images.
Refocusing (what a horrible pun) on the original objective is good.
Any time your see never-never land please yank me back !!!

God Bless America and Vacuum Grease.

Richard:)

bglick
2-Jan-2009, 18:42
> This is all reflection off the undeveloped out-of-box film emulsion.


Yes, its reflecting, but not necessarily from a fixed flat surface. You are treating film as if it was designed for use as a 1/8th wave first surface mirror?? Film is made to absorb light, not reflect it.....you are making waaaay too many assumptions here.




> When the film is not flat we get a "circus-mirror" effect

Even though I still can't grasp your premise....what good is this technique? You take unexposed film, expose it to light, confirm it gives you a mirror like surface with your trained eye, now what? Toss the film in the trash? I don't get it?



> Like mounting film on a drum scanner press to lightly and it will not go flat, press to hard and you'll put ripples in the emulsion, even with another piece of film or optically clear acetate on top for protection.


I have wet mounted thousands of pieces of film to drums, I always pull hard to create flatness, I have NEVER once experienced ripples in the film???? Maybe the scan results confused you? I know at least 10 people with drum scanners, this has NEVER been mentioned by anyone, ever, in the last 15 years. When you mention, the ol' Tango wet scan method....there is nothing old about it, we still do it the same way today...



> What I saw snap into focus at almost a point floored me (90mm Schneider Angulon at f22).

yes, on-axis, you probably saw near diffraction limited resolutions of 70 lp/mm. No surprise here. If you really want a retina orgasm, try a Canon 200mm f2.0, delivering 750 lp/mm at the image plane, magnified with a 2mm EP (125x). Aerial resolution is unfortunately not what we can resolve...



> So I've concluded that a 400X microscope with stand is the probably capable of measuring the lp/mm metric of any lens made


CS is checking high rez 35mm lenses at apertures in the f1.x range.... you are checking LF lenses in the f16+ range.... 400x is too much magnification to properly assess what can be resolved at f16+, it's not the right tool. I provide the method for determining the right fl magnifier to use, in my previous posts.



> The 35-40x Loupes good for everyday AA wannabe photographers with old reconditioned (undergone optical surgery) eyeballs.


Rich, I use loupes from 5x to 125x to examine aerial resolutions - based on the f stop they are being examined at..... more magnification is not "better" as you are suggesting. Using too much magnification, you can't see the target you are trying to resolve...you will only see the edge of a line, from this, you can not assess if it's "resolvable"... understand? The goal is, use the right size magnifier so you can "see" the targets large enough to asses whether they are resolvable.




> If I may be so bold to suggest that this may arguably be similar to the classical differences between the theorist and experimentalist,


Rich, you continue to suggest I am a theorist.... I have more test gear in my studio than most photo companies own. I am obsessed with testing things. I use optical theory to design the test, so the test is sensible and the results useful. Without optical theory, how would one understand what to test, and how to evaluate the results?



> The only thing that has changed is the common availability of a more powerful optical tool (pocket microscope/loupe). In theory it removes more uncertainty from the process of conformal focusing (like my old eye balls).


" Common availability " of loupes is whats changing the world here? Magnifiers for the purpose of whats being used here, have been around since the early 1900's in almost all fl's from 2mm to 50mm. (5x - 125x)......and since we only use them to view on-axis, they have not improved substantially, at least since the 50's. Astronomy Eye Pieces are the best magnifiers for on axis viewing....as you know, they have been around since the 1600's.


No comments on the photon accelerators, as this is a photo forum. But I think Nate is on target here...you started on-course... just like every 2 years, this forum is hit with the "I wonder if gg / film alignment is accurate enough, and if I improve it to .001", I can enlarge to 100 ft, or get equiv. 400 MP size files. Anyway, from there, I offered suggestions to steer you back on the tracks of reality, and somehow you drift into photon accelerators? sheeesh....


> Since I've used CS's manuscript as a starting point, and it does start out with empirical 1/r it will be included ideally at some appropriate point.


I have communicated with Charles many times, a super nice guy.... not an optical engineer. His "manuscript" (better known as Instructions he provides with the test target he sells) is useful to teach newbies how to use his chart and interpret the results. He makes an attempt to reverse engineer 1/R to determine the MTF of film....since I discussed this with him, he realized the error he was suggesting in the so called manuscript. He made it clear in the "manuscript" he was simply speculating. he has since removed his speculation on the MTF of the film. You have an old pdf file. The point is, don't put all your eggs in one basket.... more importantly, buy a good book on photo optics, it will save you a ton of time in the testing lab....


The Velvia film you show with "horns" is a bit curled indeed.... I never recall having film that curled, but it still is not that significant when you insert into a film holder, assuming the film holder holds the films edges tight....it will flatten right out....


I read your attached Hale / Sinar pdf..... this document leaves out one very important issue, what f stop was used? Sinar equipment is used 90&#37; in studios, not in the field. And also, these examples, probably shot at wide apt's AND flat subjects have almost nothing in common with your dream Yosemite shot, which has a tremendous amount of depth.

Also in the notes in the pdf, Sinar had to push the enlargement to 20x to see the image degradation in the target samples, from the "poor" film holder vs. the "good" Sinar film holder. Yes, 20x enlargement would also stress out the alignment issues, specially when combined with wide apertures. However, most people use LF to keep enlargements under 10 - 12x, as grain often becomes noticeable. But even on 4x5, 12x represents a 60" print.

You are not grasping the value of these inputs...its a classic case of, "the devil is in the details" .... as I mentioned at least 3x, this level of accuracy is VERY important, when you are shooting at f5.6 and you are shoot flat subjects.... in which I have agreed, if that is what you are pursuing, then your pursuit is worthwhile... I was under the impression you were trying to match AA's landscape shots in Yosemite.


Anyway, I think this thread has reached the point of no return.... I tried my best to help steer you in the right direction, but my comments have fallen on deaf ears. In addition, your posts are becoming more erratic, too hard to comprehend ...so best of luck with your endeavor....

rvhalejr
2-Jan-2009, 20:32
> ...
but my comments have fallen on deaf ears...


Quite the opposite. Every word you have written, every thought expressed will
be carefully analyzed, researched and studied. Your kindness in reeling me
back in is to be emulated and admired.

I just can't turn on a dime, old people get to move slow, so there you go.
Sometime the wisest thing one can do is not make any comment at all,
which I admit to be guilty of.

I apologize about the once every couple of years thing. What a pain.

I will try to be the best student of the optics discipline I can be. Obviously
there is a lot to catch up on.

I think Your wonderful. If I ever find that your speaking out here I'll be the guy
who falls to your feet and kisses your shoes, and be proud of it.

rvhalejr
3-Jan-2009, 12:19
Does any one have a source for really flat 4x5 ?

Out-of-the-box Really flat film test:

1.) Place on a glass table top, gently tap the emulsion surface with
a ball point pin. (Hint: The reflection off the emulsion should not change
where the tip of the pin touches the film).

2.) The reflection off the emulsion under bright light should look like a
typical hand mirror (no circus mirror distortion around the edges).

3.) For the mechanically inclined, a .0015" feeler gauge should not
be able to slip in between the glass table top and film. Flattened
household aluminum foil is ok (it runs between .0005 and .001")

Please Note:
I do not mean to antagonize or disrespect that part of
the LF community who feel this is a waste of time.

FYI: My Reasons are as follows (if you are curious):
A.) I would like to keep the emulsion plane as flat as possible during
exposure (and of course fluid scanning) and save the the Depth of
Focus envelope for artistic expression, stylistic preference or just
flat out cover up my mistakes.

B.) I am old, my eyesight sucks and "c" is about the size of a dime
or .2 lp/mm (at least ten times worst that the average photographer,
I did have razor sharp vision when younger).

Instead of giving up on photography I use focusing aids, a 35x loupe
for 45. I count it as a big blessing that I can still rack in an image
across the entire frame with simple tools. It is another blessing to
get a really big image into PS to blow it up and look at the detail.


Thanks for the understanding, kind words and your time.

AutumnJazz
4-Jan-2009, 09:27
Do lenses even resolve enough lp/mm at F16 and smaller to even warrant something like this?

The page linked below seems to indicate that defocus and diffraction severely handicap any lens' resolving power.

rvhalejr
4-Jan-2009, 13:23
Do lenses even resolve enough lp/mm at F16 and smaller to even warrant something like this?

The page linked below seems to indicate that defocus and diffraction severely handicap any lens' resolving power.

I am a subscriber to the theory that the effective diffraction limit is twice the value often cited by what I believe is the standard calculation. I've seen absolutely no problem with that or defocusing when using the loupe/plenum technique, other than vastly improved control over the final image and far better insight into the finer points of LF photography, simply because everything is resolved so much better.

That you have to ask that question is very, very sad. The zealots seemed to have convinced us that at f16, one of the better resolving settings for published lp/mm data are of little value in the field with a view camera.

My experience is that the device at f32 is very useful (often with a
hood of course) and may be so even smaller, perhaps including camera obscura (I'm now putting on body armour and helmut).

The "something" referred to is a product, part of a "business", that does not make enough profit to pay for my 4x5 film (which under a bright light has a circus mirror emulsion reflection that even the critics admit disappears when pulled and taped down for a fluid drum scan).

I can honestly say I love using the 35x loupe/plenum combination and NOT ONE HAS EVER SENT BACK FOR A REFUND which I would be more than happy to do if it does not suit any photographers technique or needs (absolutely no problem).

It may be possible that there is an Ideal replacement for the bright ground
glass and Fresnel lens combo I use, perhaps negating the need for the plenum.

But at this moment I do not believe that is generally the case. Even if it
were, the 35x loupe would still work the same (in theory anyway).

One thing I'd like to see done is the taking and publishing of the measurements for defocusing (I'm assuming you mean the Depth of Focus {DoFocus} at the Emulsion Plane after it has been carefully aligned with the Image plane for the final Image Rack-In).

If you (or an author, instructor, etc.) would like to do that I think it would be great. If nothing else it would better define the DoFocus envelope under various conditions (including, hopefully, a few test cases with basic movements that I use).

I would like to see more information published on the use of small optical pocket microscope systems to evaluate and characterize Optical LF systems.

I've never believed that characterization of SLR, MF, LF and ULF systems would (as the critics would have us believe) be EXACTLY(sic) the same. Yet It seems that the opposite may also be true, that there should be some reasonable similarities while giving recognition to the limitations imposed by optical boundaries.

Sadly, I do know that I'll never be able to investigate all the optical opportunities the Loupe and Plenum combination affords. My hope is that others will and thus provide a generally accepted incremental improvement in the discipline in some small way.

I'm also burdened by the knowledge that the work CS may
have been deprecated here. I ask forgiveness as I forgive those who may be imperfect as I certainly am.

All the Best to You and Yours and God Bless ALL on this first Sunday of the New Year.

AutumnJazz
4-Jan-2009, 15:07
Whoops, forgot my link... http://www.largeformatphotography.info/fstop.html

rvhalejr
5-Jan-2009, 11:37
Thanks !!! A perfect citation !!! I did not want to see this painful comment on the first page though:


... Film flatness is more problematic with LF than with other formats ...

Amen

I'll be looking at the pro/con issues in hopes of aggregating a generally acceptable summarization.

rvhalejr
5-Jan-2009, 11:47
Does any one have a source for really flat 4x5 ?

Out-of-the-box Really flat film test:

1.) Place on a glass table top, gently tap the emulsion surface with
a ball point pin. (Hint: The reflection off the emulsion should not change
where the tip of the pin touches the film).

2.) The reflection off the emulsion under bright light should look like a
typical hand mirror (no circus mirror distortion around the edges).

3.) For the mechanically inclined, a .0015" feeler gauge should not
be able to slip in between the glass table top and film. Flattened
household aluminum foil is ok (it runs between .0005 and .001")



Photographing the mirror like reflection and posting the image gives
validity to test. It's not easy getting a useful digital image of
a near perfect LF emulsion reflection.

I just wanted to share that I used a 2x flip-down magnifiers on my
crappy old D100 and S2 .,. seems to help .,.

bglick
6-Jan-2009, 19:02
I am trying to stay away from this thread, but nothing worse than mis-information still being spread.....


> Photographing the mirror like reflection and posting the image gives validity to test.


The only validity to photographing a films surface is.... you will potentially demonstrate that film does not have a front reflective surface, and therefore will NEVER reflect a perfect image like a front surface mirror will. Film was never designed or tested for wave front errors.


To get to the beef of what you are trying to ascertain.... you should test some film holders for plenum flatness. Record values at different XY coordinates. Use a high tolerance straight edge (<.001" per 6") and dial indicator, .0005" or better. The set-up is called a depth gauge, where you plunge the dial indicator down until it makes contact.

Next, insert film into film holder, run the same test at the same coordinates. Use a good light, you can easily see when the guage pointer makes contact with the film. (of course, you must account for film thickness) These are the results that matter - not using film as a mirror . With good 4x5 holders, the film probably will not bulge more than .006" vs. the previous plenum readings. At f16+ apertures, errors in flatness at this level will be undetectable in the final image, even when imaging flat subjects. See Depth of Focus above...

Nathan Potter
6-Jan-2009, 19:48
Well I'm also trying to stay away from here. But there are other techniques that can be used to check film flatness. They involve interferometry. The simplest would use an optical flat and a monochromatic light source. You'd need an 8 inch diameter flat to cover 4X5 film. You could use a sodium lamp. Since film is very flexible you can't place the flat right on the film surface since it will (the film) deform to the flat. So you need to suspend the flat just above the film say by .020 inch. Then count fringe displacement. I say this but I'm not sure that most film has adequate reflectivity for this technique as bglick has mentioned.

An entirely more elegant method is to use a projection interferometer such as manufactured by Tropel Inc. Again film reflectivity may be an issue.

rjhalejr, examining a reflected image of a straight line say from a bright lamp could only yield qualitative information about the degree of flatness and not real hard numbers. And again your concern is how the film sits in a standard holder so the dial gauge scan of film in holder as suggested by bglick seems like a feasible way to collect some decent data. But even with that technique you don't want to depress the spring loaded back.

Nate Potter, Austin TX.

bglick
6-Jan-2009, 20:18
> Then count fringe displacement. I say this but I'm not sure that most film has adequate reflectivity for this technique as bglick has mentioned.

> An entirely more elegant method is to use a projection interferometer such as manufactured by Tropel Inc. Again film reflectivity may be an issue.


Nate, you correctly point out, all these methods are dependent on film having a single reflective surface. I can assure you, this is not the case. Film is partly transmissive, otherwise rays would not hit the film grain below the surface. So light scatter and light reflectivity can ocurr at many depths. I never tested this scientifically, but its just obvious...

More importantly, the mechanical testing method is so simple, and has accuracies in the magnitude of 10x greater than what is required, and it cost $100....why look any further?

rvhalejr
7-Jan-2009, 14:41
rvhalejr, examining a reflected image of a straight line say from a bright lamp could only yield qualitative information about the degree of flatness and not real hard numbers. And again your concern is how the film sits in a standard holder so the dial gauge scan of film in holder as suggested by bglick seems like a feasible way to collect some decent data. Nate Potter, Austin TX.

NO.

Quantitatively (in a meterology lab) the runout (dial indicator readings as its swept across the surface) should be with +/- .0005" if you have fastened the film correctly by rolling and taping it (for a an in-the-limit fluid scan or perfect mirror image as has been provided more than once here in the form of an image).

I am more than willing to try and help anyone take any type of picture they want.

The problem with the dial gauge is that when it contacts the film it may read inaccurately if there is any gap between film (and septum, plenum, glass table top, etc.) and a good metrological granite surface plate.

I was going to mention temperature normalization but it seems the film may curl after twenty-four hours because fluid scanning tape is not that strong (since film was tugged on it acts like a spring).

How the film sits in the holder is not of much concern UNLESS it deforms the film in some manner (visual deformation is just sooo... gross), not a common problem with high end holders. The cheap wooden ones need inspection and adjustment but good ones can hold flat film within +/- .001 which is probably good enough unless we insist on compounding other errors.

Newton's Rings
Place a piece of glass on top of any film (on a glass table top) and you will see Newton's rings. The highest quality flat bed scanning can be accomplished within glass sheets on top and bottom (a glass sandwich so the embedded software/firmware can work really good). The problem is that Newton's rings will end up in the image so the method cannot be used (sigh).

Place an optical flat on film lying on a surface plate and your readings will be perfectly flat for any film suffering from out-of-the-box film curl because the weight of the flat is acting like a press, squishing it nicely into place...you might prop the flat up matched feeler gauges (or gauge blocks) but film variations will probably be constrained by the flat itself.

That's similar to the reason why I'm apprehensive about the run out with a gauge. If we see any deformation in the reflected image (where the probe intersects the film) we will not have an accurate reading (worthy of certification).

*** HOWEVER *** A good metrologist can develop good "touch" with the technique AND hit accuracy better than .0005" !!! Sooo... if bg is relaxed, and careful he can get a perfectly certifiable measurement for film out of the box if its curled or not.

A good metrologist will often photograph their work and include it in a document signed off by managers, at least one state representative, and engineers certifying to the accuracy and correctness of the measurement to specified standards for ASME Safety Related Items.

That is why I have provide images to this thread, as part of the certification process. I did not expect others to be so photographically challenged.

This may mean using a tripod, close up lenses, dslr, light metering, careful attention to lighting, planning, using auto focus, being able to differentiate between distortion or lack there of and so on .,.

Sorry for all the metrology, but I'm way out in front of this at f32 (under the hood) with the near target at 7ft (bottom of 4x5 frame) and the far target at 20ft (top of 4x5 frame) and the third target anywhere in-between, starting to plan the validation of tilt (and swing) with the 90 degree and pre-set 75 degree loupe(s).

I've learned more about that this morning. To make it idiot photographer proof (for me) I need two reference points to provide no-brainer radial and tangential alignment marked or etched into the glass (to line up the 75 degree stand arrows with those points on the glass/acrylic plenum in the dark).

If I had to guess right now i'd say it might work at f64 but its going to be very, very dim. Maybe a small patch of etched glass may be used to "light up" the correct positioning of the near far targets (using reflectors or photo lights). But f32 is definitely do-able with some not so insignificant study and work.

bglick
7-Jan-2009, 16:16
.


This is starting to become comical....

> The problem with the dial gauge is that when it contacts the film it may read inaccurately if there is any gap between film and septum.


For those interested.... you simply push the dial gauge probe downward, till it makes contact with the film.... with a good light and and 3x glasses, its very obvious when it hits the film... record this value. Since we know the distance the plenum lies, and we know the film thickness, all that remains is the air gap between the film and the plenum. It doesn't get much easier than this when it comes to testing....




> That's similar to the reason why I'm apprehensive about the run out with a gauge. (worthy of certification).


First, who is certifying this? For what purpose? How did we go from a rough check, to certifications?




> If we see any deformation in the reflected image (where the probe intersects the film) we will not have an accurate reading


Accurate? how accurate do you need it? Even if you only hold accuracy to +/-.002" with the prob method due to bad eyes, weak light, or bad technique, that is 8x greater than the worst error you are searching for? I still don't think you have comprehended this, because you are still NOT comfortable with the Depth of Focus principle.




> A good metrologist will often photograph their work and include it in a document signed off by managers, at least one state representative, and engineers certifying to the accuracy and correctness of the measurement to specified standards for ASME Safety Related Items.


I must have got lost somewhere, I thought this was about a simple reality check "test" to assure you have sufficient film flatness to take pictures of Yosemite as a hobby. How did this home hobby test, elevate to the level of needing State Representatives signatures and engineering certifications? Huh? Anyway, I will let you have your fun .... I couldn't help responding to this one.... Maybe you were being humorous, and I just didn't get it.... I hope a newb doesn't read this thread, he will go back to digital :-)


And after you have Mastered Depth of Focus to simplify your life, I STRONGLY recommend a book on lens tilt by Harold Merklinger. You should rip through it in a few hours, it's the Bible of lens tilt. It is in book form, and now free in pdf some where on the internet.... have fun....

D. Bryant
7-Jan-2009, 16:25
I hope a newb doesn't read this thread, he will go back to digital :-)

Well if they do they will surely need this:
:)

http://www.rawworkflow.com/lensalign/

rvhalejr
8-Jan-2009, 12:26
Whoops, forgot my link... http://www.largeformatphotography.info/fstop.html

“Some people think that instead of using all that math, you should just rely on inspecting the GG”

Sure, follow the path of least resistance. Sometimes use air (or clear glass) to remove all grain with the aid of a flexible and powerful magnification device (loupe). The math will work itself out later.

“When you stop down, it gets pretty dim, especially through a lupe in the corners of a wide-angle view”

I think what QT Luong was observing might have been occlusion from not using the required loupe stands for sides, top and bottom of frame (my reference is a Schneider 90mm angulon).

The loupe stand angles for 4x5 are roughly 90, 75, and 65 degrees for center, side and corner.

The loupe stand angles for 8x10 are roughly the same plus a corner stand at 55 degrees.

There is little fall of in the corners with a good lens that covers the full frame with the correct loupe and stand at f22 or wider (you may not need to use the dark cloth hood if light is not hitting the back of the camera directly).

The f-stops at or above f32 pose special challenges because of the lack of light, I can resolve CFLs at about 7 feet (bottom of frame) and 21 feet (top of frame) indoors (which I think is about the limit for a normal household ceiling and floor. What resolves is exciting in that the near far targets are much sharper than f22, but I do not feel comfortable working at that pay grade until there are some tools that will make it easier. The practicality of using near far reflectors or lights is also in doubt.

Testing of movements and examination of models and sketches (i.e. Wheeler's rule of 60) indicates there are likely to be issues with tilts (and swings). I've rarely used shifting and tilting and have to come up speed and working in very very dim light is difficult. Shifts seem to be easy, tilts are going to take some work.

In passing it should be mentioned that Full Open is ok (for background blur) but be sure to check for occlusion in the corner of the frame by the lens throat before hand (you do not want to be in the penumbra). To do this you must put your eye in the corner (no back or gg ) and check lin-of-site to the aperture. If the opening is round you are good, if its out of round do not use that f-stop (unless you like the vignetting).

Thanks again for the URL, I still need to talk about a few more things .,.

rvhalejr
8-Jan-2009, 13:01
And after you have Mastered Depth of Focus to simplify your life, I STRONGLY recommend a book on lens tilt by Harold Merklinger.


I would like to do Master Depth of Focus (DoFocus) as you have described. But where I depart from your generally accepted prospective is to better define the use of the envelope's interval such that it may (under some conditions) be exploited.

All of your previous posts (going back to 1999 ?) are very insightful.



it's the Bible of lens tilt. It is in book form, and now free in pdf some where on the internet.... have fun....


In addition to Mastering Conventional DoFocus fundamentals I will try to get a hold of the Bible of lens tilt by Harold Merklinger.

I would like to request one sheet of out-of-the-box film from any member of this most esteemed forum who has the time, for a little dimensional characterization, and statistical analysis, just for grins.

The goofy math side of me would still like to calculate the distortion (if any) of spatial frequencies in an USAF target exposure on film that is curled verses that which is not, just for grins.

All the Best,

R.

rvhalejr
8-Jan-2009, 15:37
Here are a couple of posts (some old) some of you may want to comment on:

... largeformatphotography.info/forum/showthread.php?p=422634#post422634

This post expresses the idea that lp/mm lens data can match up with the generally accepted characteristics of a lens.

... largeformatphotography.info/forum/showthread.php?p=155415#poststop

This post expresses the idea that APOs are lenses that have smaller than normal wavefront errors. Perhaps this is contrary to the sentiment expressed by one (of a handful of large web) personalities (ba thinking, perhaps indirectly referenced by bg earlier) that spherical aberration is mostly wavefront error and thus lp/mm measurements (as cited in the first url) should not be used because (we cannot be sure someone skipped a patch and is using a subsequently spurious resolution, or they took the measurement wide open and must be messing with the mathematically imaginary wave front interval) even though it gets better than reported values at f8 and higher (which surprise !!! looked way sharper and way dimmer) .,. Is that the executive summary ? .,.

I'm now chumming the water for more great white sharks .,.

Also, excuse my ignorance but by pointing the really cool DSLR calibration tool (Twice so far?) while most seem to agree feel that "we do not need no stinking lp/mm tests" is just to good to resist. .,. :D

In the off chance ANYONE out there would see any value in doing something similar for LF before its patented (Sand bag on ground @ 6ft from lens, tape measure extended to top of BIG light stand at 30 feet from lens, with aircraft warning light on top) ? These distances just happen to land at the bottom and top of the 4x5 frame behind a 90mm lens with which I hope to use some ideas from the tilt bible). I would assume that lp/mm targets at near, far and somewhere of to the side (in the middle) form a plane in which to take and compare lp/mm reference points (or not)?

Well, off to study the DoFocus Masters and why newb(s) should use curled film out of the box and not question the all powerful DoFocus. Here sharky sharky, .,.

R.

rvhalejr
10-Jan-2009, 16:28
I must have got lost somewhere, I thought this was about a simple reality check "test" to assure you have sufficient film flatness to take pictures of Yosemite as a hobby.

Sure, and thanks for your contribution to that :^)


How did this home hobby test, elevate to the level of needing State Representatives signatures and engineering certifications? Huh?

Well... Beyond the Park Pictures I've been toying with the idea of using the 4x5 press for (and maybe its cousin the view) Architectural work or maybe as a tool to help document large engineering projects (in a former life).

That type of LF photography seems to offer the benefit of a wide perspective and a high degree of precision. Hence the possible value in quantifiable or even certifiable results at some point. An Architectural subject like that is just up the road from Yosemite called Hetch-Hetchy, a big dam and lake that holds a lot of drinking water. Power plants and those new giant wind mills might be good to

Anyway, I would like to model basic tilt scenarios and put them in a spreadsheet or two since that is a known method for making life easier.

The coc (airy disk in the emulsion/image plane) that I believe I'm after is .001" or .0254mm which is as small as I can make out with a Carson 40x Loupe[1].

That can be repeated by looking at gap between the .0015 and .002 feeler gauges (stuffed together in a slit cut into cardboard with a box knife). Optically, the DoField of the 40x Loupe is very small (as one would expect).

We can exploit that when looking for a .001" dot in the Image Plane to directly measure the in/out delta for the DoFocus Envelope (90mm Angulon at f32).

As we rack in and out the entire distance is probably all DoFocus in the emulsion/image plane. A .001" airy disk may not be resolvable behind the 90mm Angulon at f32 (as a table included in this thread seems to indicate) but .002" is probably more than good enough for the informal evaluation of Sharpness verses DoFocus I'm trying to do (along with tilts thrown in for good measure, which are new to me).

The Focus/Check[2] procedure seems like a good place to start for a tilt newb, it might make sense that the last Focus/Check be done where the 40x loupe is an option.

I may be getting Pc and Pf mixed up (I'm dyslexic and old) as far as their repective importance goes, but maybe real world tilt is about balance between the two points (whats on the ground verses the subject which is further away, maybe beyond hyperfocal distance).

As a practical matter I need to fashion some dowels for the Speed Graphic so I can hold a tight tolerance in the lens board tilt angle (thank goodness the bed drops down and the front standard can be taken off the rails for tilting using the edge closest to the bed as a hinge).

The dowels need to be selected for 0, 5, 7, 9 and 11 degree tilting (My best guess as for the most use full tilt angles, I could be wrong).

I'm still looking for the simplest equations that can be translated to the focus check procedure in the field, can be sketched easily and be put in a spread sheet or two.

I should probably include the 8.5 x 11" cheat sheat but its on the other computer that needs some re-wiring (the cat must have gone wild last night).

I'm hoping to come up with some sketches (from the tilt cannons) for the back of the 8.5 x 11" cheat sheet that will show how to take measurements in the field (for most situations) and then plug them into the spread sheet or manual calculator as some have done.

Notes:
------
[1] Carson 8x20mm Monocular, 5x Stand Magnifier, 40x Microscope With Default 90 degree stand, I craft a few stands now and then for the 75 and 65 degee tilt on the gg for side and corner of the 4x5 glass plenum

[2] Ref ... largeformatphotography.info/articles/bond-checklist.html



And after you have Mastered Depth of Focus to simplify your life, I STRONGLY recommend a book on lens tilt by Harold Merklinger. You should rip through it in a few hours, it's the Bible of lens tilt. It is in book form, and now free in pdf some where on the internet.... have fun....

Merklinger is impressive, there are some triangles in there that look promising.,.
...
Yep, Thats what LF photography is all about. It would not be fun if it were all about work.

bglick
10-Jan-2009, 18:32
> A .001" airy disk may not be resolvable behind the 90mm Angulon at f32 (as a table included in this thread seems to indicate) but .002" is probably more than good enough for the informal evaluation of Sharpness verses DoFocus I'm trying to do


I can't tell if you genuinely want help, or you are using this forum to run a blog on your current LF learning experience? But whatever, with the numbers you present above, you have reduced your capture down to about 24MP camera... that's OK, but vs. the 400MP goal you initially aimed for, its quite a reality check, huh....


I have asked many times about the 40x loupe...but you never answer... what are you viewing? The gg? If so, this is so overkill, its not even useful... a gg can resolve maybe 4 lp/mm max., so any 3x loupe is suitable...



> As a practical matter I need to fashion some dowels for the Speed Graphic so I can hold a tight tolerance in the lens board tilt angle

Or, just tack on this instead, accurate to within +/- .5 degrees.... no dowels required, unless you desire the cumbersome work. In addition, degree spreads are quite large for WA lenses. The beauty of these electronic gauges is, you can check both the front and rear angles, as the net effect of front tilt is, front tilt - rear tilt.

http://www.wixey.com/anglegauge/images/top06.jpg

http://www.wixey.com/anglegauge/index.html

rvhalejr
11-Jan-2009, 02:10
> that's OK, but vs. the 400MP goal you initially aimed for, its quite a reality check, huh....

I respectfully disagree. Analysis indicates that 200MP has been the yield for 4x5 for about eight years now if the numbers RC published are still true. If 200MP can be proven then 400MP becomes much more realistic. I just cannot say that my critics will comprehend or approve of the method, yet.

If I had your 4x5 back I might never touch film again and be making the same arguments.


>
I have asked many times about the 40x loupe...but you never answer... what are you viewing? The gg? If so, this is so overkill, its not even useful... a gg can resolve maybe 4 lp/mm max., so any 3x loupe is suitable...

...largeformatphotography.info/forum/showthread.php?p=423824#post423824

I respectfully disagree with your logic, your numbers, your technique and conclusions. You do understand how the 40X is used, I've provided plenty of pictures and pdf files, and you have reached the conclusion that it is not suitable. I respect your position but need to wait and see what I can come up with.

I think even you would have to admit focusing with a 40x loupe and clear glass plenum would be far more precise than something much less powerful, huh ?

I resolved 100 lp/mm with the 90mm Angulon at f8 so its just a matter of getting it on film and scanning, right ?

Once I get a vacuum or plenum film holder prototyped I will begin the hunt for the right lenses and settings to obtain the 200MP yield. I also already told you how to double the yield of any film, which you already know.

What we disagree on is that it will yield anything useful. You claim that it will not and cite sources. I think it will and can use citations from your sources to make my case.

> As a practical matter I need to fashion some dowels for the Speed Graphic so I can hold a tight tolerance in the lens board tilt angle



Or, just tack on this instead, accurate to within +/- .5 degrees.... no dowels required, unless you desire the cumbersome work. In addition, degree spreads are quite large for WA lenses. The beauty of these electronic gauges is, you can check both the front and rear angles, as the net effect of front tilt is, front tilt - rear tilt.


Very sweet gadget indeed.

bglick
11-Jan-2009, 09:44
> I respectfully disagree. Analysis indicates that 200MP has been the yield for 4x5 for about eight years now if the numbers RC published are still true. If 200MP can be proven then 400MP becomes much more realistic.


Rich, you never explain, "how" or "why" you disagree. I provided all the numbers in the previous posts to explain why your 200 / 400 MP value is so far from reality. Why don't you take the time to explain "what" in particular you "respectfully disagree" with?



> I just cannot say that my critics will comprehend or approve of the method, yet.


The entire world knows what the max. resolution color film can resolve at each f stop. Unless you defy the physical limits of imaging, then your 200 / 400 MP values are smoke n mirrors.... you are still fooling yourself... and it doesn't seem as if you want the true answers.... Basic imaging premises such as 1/R and DofFocus you are still not embracing. As a scientist, you should consume these conventions, like crumb cake with your coffee.



> If I had your 4x5 back I might never touch film again and be making the same arguments.

Why? My film holders / back are like most others, off-the-shelf with no modifications, as none were required....



> I think even you would have to admit focusing with a 40x loupe and clear glass plenum would be far more precise than something much less powerful, huh ?


As mentioned previously, its according to what you are focusing on. If your goal is to do a film test, the film focusing loupe is way to unreliable.... as mentioned in my previous posts, you have way too many variables. Instead, shoot some test targets several times...first best focus on the gg, then move the back standard up n back in .003" increments with a dial gauge. maybe 6 shots total. The processed film will answer all your questions within a day. (where is best focus, and what can yo resolve to film) You will also determine EXACTLY how much you resolved on film and lay to rest your claims for 200/400 MP images. Or you could keep this blog running for a few more months .... which makes more sense?



> I resolved 100 lp/mm with the 90mm Angulon at f8 so its just a matter of getting it on film and scanning, right ?

NO! You may have resolved 100 lp/mm in the aerial resolution....but run this through 1/R....then you will get a "best case" resolution on film....and that is what matters here, right? So to answer your question again, NO, you can NOT get 100 lp/mm on color film .... which is what this discussion was about, right?



> What we disagree on is that it will yield anything useful. You claim that it will not and cite sources.


I am not citing sources, I am simply applying basic imaging concepts that are proven, and have been been around for 50+ years, embraced by Zeiss, Leica, Schneider, Fuji, Kodak, etc...and I am applying them to what you are proposing.


You do realize, for your claims to be accurate you will have proven all these makers wrong.... all their research and millions of dollars into testing by the worlds best optical engineers will be proven faulty by your 35x Carson loupe and clear glass plenum....hmmmm.... do you really think that is possible? Its not like these are secret formulas and can't be tested, as the rest of the imaging world, like myself has confirmed these princlipes for many years.

You do realize your position is : my 35x Carson loupe will prove Zeiss, Leica, Fuji wrong in what they have demonstrated for the past 50 years. All their testing, and the millions of people who have tested the same, are all wrong, as this thread will rock the imaging world...right?



> I think it will and can use citations from your sources to make my case.


Please advise us how we can get the yields you propose? What lenses, what f stops, what film, what type of subjects (with or without depth) will yield 200/400MP images? State specifically for us, OK Rich? You seem to be ultra scientific, so you must provide details, as your general statements just keep this thread floating in "the land of mystery" ..... or maybe that is how you prefer it? If you want help, people will provide it, but I still think that is not the case...

rvhalejr
11-Jan-2009, 18:35
> I respectfully disagree. Analysis indicates that 200MP has been the yield for 4x5 for about eight years now if the numbers RC published are still true. If 200MP can be proven then 400MP becomes much more realistic.

Rich, you never explain, "how" or "why" you disagree. I provided all the numbers in the previous posts to explain why your 200 / 400 MP value is so far from reality. Why don't you take the time to explain "what" in particular you "respectfully disagree" with?

> I just cannot say that my critics will comprehend or approve of the method, yet.

The entire world knows what the max. resolution color film can resolve at each f stop. Unless you defy the physical limits of imaging, then your 200 / 400 MP values are smoke n mirrors.... you are still fooling yourself... and it doesn't seem as if you want the true answers.... Basic imaging premises such as 1/R and DofFocus you are still not embracing. As a scientist, you should consume these conventions, like crumb cake with your coffee.


There is a very simple way to test this, but like so many in the LF movement school of thought your are stuck with a circus mirror brick wall limit. It kills me to see you so anal retentive about the analogies I try to draw. I'm one of a very few who can show you how to do it, how to prove it, and hopefully contribute to its usability in some small way for reasons that may sometimes need be expressed in between the lines.

I've never expected more than a handful of experts to achieve that level of yield, the effort justified only by the certainty that a masterpiece is being recorded.

What follows is both amusing and in code, So get a good cup-o-joe and a cookie and read it carefully (probably best in the morning) with the knowledge that you have been gracious enough to let me learn how you think.

I told you about a film under the microscope study that produced hundreds (if not thousands) of micro-photographs verifying the thickness of the emulsion (about .001" to .0015") and the base. In another one of your earlier post someone pointed out the MP limit of 35mm as determined by FBI forensics but I'm not sure you ever recognized that (when marching in the circus clown mirror and mushy movements parade).

On the other extreme side of the scale (to the very far) I brought up the Hubble and what failure to test the optical system resulted in. I've worked with remote sensing images, that means something like the Hubble pointed at the ground and mapping the surface, and even though Google maps can show the street any of us live on, from space, much of that technology (for on orbit and air breathers) still remains sensitive. All this from 1/R and a lot of other complex variables.

There are a lot of ways to analyze an Image and I'm sure there exists some outdated science somewhere buried in an international military, forensics or reconnaissance organization's vault that confirms optical limits and resolving properties of film far beyond what the circus mirror clown parade believe that their tilt bible preaches about the DoFocus envelope in every possible instance of the near and far.

I'm saddened by all the marketing hype about MP that comes by every couple of years. But that's no excuse for implying that lenses do not exist with resolving power that was designed to maximize resolving characteristics and fit in a 4x5 frame . I'm sure none of the lenses you own are likely to yield whats been suggested as a requirement, which is nothing more than a good APO high lp/mm and flat profile lens. :rolleyes:

But because of the thrashing CS got I have no expectations as to the circus mirror mentality ever caring consider that photons are photons whether traveling through a microscope, telescope, linear accelerator, slr, mf or lf camera. The fact that weight is no longer given to lp/mm profiles by BA speaks volumes. I have no doubt that when he takes a mushy lens and tilts it that the image resolved is a result of intentionally distorted circus mirror wave fronts. This does not invalidate the optics and physics outside the lens tilt circus mirror domain.

The optics that worked for reconnaissance in WWII (on 5” wide roll film if a recall correctly) can still be observed with the USAF lp/mm target today when used with skill and precision (as suggested in yet another previous post). The benefits of Precision Fine Focusing seem to be recognized by European and Asian lens manufacturers and photographers. Not so in the US. Granted sometimes Precision is emphasized to such an extent that it becomes amusing, but it can be a good thing to have a muse of which the circus mirror lens tilters should not be exempt.


explain, "how" or "why" you disagree

The How regarding best possible Focus: The one and only plane of sharp focus can not be allowed to move out of parallel with the emulsion plane, both of which are constrained by a flatness "rule of thumb" requirement of no greater than +/- .001" (for precision purists). Recognize that for all intensive purposes both planes are one and the same as verified by an out of camera optical system with a magnification of no less than 35X.

The Why: The limit of resolution for these conjoined planes is that of the airy disk (a good approximation of the perfect point). Calculated diameters as a function of f-stops should not be considered empirical limits due to intentional variability in designs, manufacturing and desirable characteristics. OEMs will exploit sharpness optimization, when given the chance, beyond what simple calculations indicate (presumably fractional wave front formula tweaked with super computers).

Within these high precision APO lenses are bound to be designs known to be brutally sharp and verified by solid lp/mm characteristic profiles. But they become more difficult to evaluate at ever smaller spatial frequencies with simple methods. Using an 100x to get a high 200MP yield would be a lot of work even with tool sets designed specifically for the job.

I feel no need to rock the world with stratospherically high MP yields. A 35-40x loupe is a lot easier to use than a high power one, so its a nice comfortable compromise. If I recall correctly above 100lp/mm may require the 100x or higher to resolve the lp/mm patches without skipping one and introducing spurious resolution. The field of view is so small its like the patches are 8.5x11 paper on a football field from a mile high (or couple of kilometers) in an air plane. Its hard to find the football field much less sequentially evaluate the targets without getting lost.

Given the practical magnification compromises with the loupe, a reasonably priced lens could be selected to match performance, that is why the 90mm Angulon , a common not so expensive as the Super Angulon (which is likely more capable of stratospherically high MP yields than its cheaper cousin) is used in everyday tests.

I'm simply scaling back expectations (monster MP yields) to place the emphasis on ease of use whereby the focus/check procedure remains enjoyable instead of becoming a frustrating task requiring a lot of labor and time.

There are some films that are expected to yield no significant improved resolution due to their unsurpassed realistic color rendering and diffusion characteristics. As a footnote films can be E6, C41, BW and/or duplicating which is known to be as slow as ISO 12 and maybe lower, what does that do to your noise floor and Yield ?

bglick
11-Jan-2009, 19:22
.

Rich... you mentioned the word stratosphere many times.... and IMO, that is exactly where this thread is now...... or somewhere between the stratosphere and the Hubble Telescope you designed, which is floating out in space. Most of your post, I simply can not follow ...you are jumping from

"circus mirror brick wall limits",
Hubble errors,
wavefront errors of photographic film,
linear accelerators,
WWII Reconnaissance cameras,
"mushy movement parades".........


All along, I thought this thread revolved around film flatness and OFR. In the end, this simple photographic endeavor might be too simple for a man of your intellect... just a guess. Einstein had to find someone to tie his shoes...?


I will leave you with my final thoughts...then you can have free reign, and continue your blog (this thread)....


> The How regarding best possible Focus:

Your desire and justification for this has obviously not changed since your initial post. Therefore, you have clearly NOT embraced the basic optical principles that set these limits, which i wrote too many times to repeat. As I suggested earlier, you are on-course to prove Fuji, Leica, Zeiss wrong about their published findings for well over 50+ years. (when MTF became widely accepted) I wish you luck...it's a heck of an endeavor with a $35 Carson Loupe as your main tool.


> The Why: The limit of resolution for these conjoined planes is that of the airy disk

This is false, and you still have not accepted 1/R... as simple as the formula is, .... and as scientific as your background suggests, this baffles me. But it's your hobby, so run in the direction that brings you happiness. At some point, I can assure you, all roads lead back to

1) 1/R,
2) apt. diffraction limits and,
3) the MTF of film.

You have set-out to defy these rock solid principles.... which have been proven over and over again for the past 50 years. In addition, i am sure you would agree that a digital sensor is FLAT.... if you use a digital senor on the back of a 4x5 camera, you can test all your lenses, as the resolution of the sensor is quite obvious.... you can adjust the sensor plane with the focal plane till its just perfect.... then, you can also test DofFocus. These back adapters can be had relatively cheap...then just hang a DSLR. It might start to convince you that 1/R sets the limits. Google Nyquist, you will find enough reading material for a few days...it represents the basic premise behind the 1/R formula.


I am sorry i can not offer anything else... so, enjoy your journey...

rvhalejr
13-Jan-2009, 12:39
... it's a heck of an endeavor with a $35 Carson Loupe as your main tool

its a 40x, any 35x to 40x will do.



...
"But we can use (B&W) films for which the MTF extends above 200 cy/mm,
the Gigabit(TM) film was available in 4x5" ! "
...
In Europe we do not recognize software patents, so all pre-processing tricks, at least for the European market, will be secret know-how. And if a company is issued a software patent for digital image pre-processing valid only on the US, taking into account that you have to disclose a minimum of technical details in a patent, this would mean that the patent is kept secret for European readers !

Ref ...largeformatphotography.info/forum/showthread.php?p=429612#post429612



...
I use an 8x10 camera and when I drum scan the image I have a 568 megapixel file.
...

Ref ...largeformatphotography.info/forum/showthread.php?p=429985#post429985

rvhalejr
13-Jan-2009, 13:57
As of this post it is clear that a 40x Carson Loupe can be had for about
$40 (including shipping).



... it's a heck of an endeavor with a $35 Carson Loupe as your main tool




... any 35x to 40x will do .,.


Ref ...largeformatphotography.info/forum/showthread.php?p=430001#post430001

As luck would have it, 4 CDs placed on the back of a 4x5 (1949 Hollywood Ready Speed Graphic - its the standard, but the experts know that) will suspend the Loupe at about the convergence of Emulsion and Image plane when positioned over the hole in the CDs.

This is a demonstration recommended for any Instructor who would like to capture the imagination of a class.

The exercise can become more academic when a piece of developed 35mm film is placed over part of the hole (the FOV of the 40x allows this) and the loupe is focused on emulsion grain in the same plane that the Lens Image is the most sharp.

A USAF lp/mm or cy/mm target can be placed in front of the camera and resolution roughly estimated and correlated to MTF measurements.


For Sale:
For normal to near telephoto lenses:
$79.95 for the Loupe (default center of frame stand).


The reason I charge $79.95 for loupe is that it includes a complete documentation set. At that very low price point support will be provided, but only to not-for-profit institutions.

bglick
13-Jan-2009, 16:27
In case your interested Rich, I responded to the post you cited above...

Just like the film / focal plane alignment comes up every 6 months, so does the 500 MP 8x10 film issue..... draw your own conclusions.


> I use an 8x10 camera and when I drum scan the image I have a 568 megapixel file.


http://www.largeformatphotography.info/forum/showthread.php?p=430059#post430059

rvhalejr
13-Jan-2009, 20:37
In case your interested Rich, I responded to the post you cited above...

:) Thanks .,.



There are some films that are expected to yield no significant improved resolution due to their unsurpassed realistic color rendering and diffusion characteristics.


Ref .,.largeformatphotography.info/forum/showthread.php?p=429492#post429492

I was kind of hopping you would run with that one, so If you do not mind me asking,
are you shooting with c41 p-nc? (message me if you do not get p-nc in a few secs,
when i'm in the c41 mood I'm addicted to the stuff) .,.

bglick
13-Jan-2009, 22:56
I only shoot chrome film....

rvhalejr
14-Jan-2009, 09:57
I only shoot chrome film....

You did not question this:

Ref ...largeformatphotography.info/forum/showthread.php?p=429612#post429612



... film transmits fine details with a low contrast well above 100 cy/mm.

But we can use (B&W) films for which the MTF extends above 200 cy/mm, {AND}
the Gigabit(TM) film was available in 4x5" ...


So are you o.k. with "well above 100 cy/mm" for chrome/e6 and
MTF extends above 200 cy/mm for bw ?

bglick
14-Jan-2009, 10:40
Two issues that people get carried away with here. First, only Gigabyte film, a B&W speciality scientific film has these extreme levels of resolution...I did try it once, its not very pleasing IMO....

Secondly, these MTF values are often stated for only the highest contrast, which is very unrealistic.... often times you can not even find targets to test at these contrast ratios, so it is impossible to shoot real world subjects at these MTF values. Hence why all our target testing of film / lenses produces OFR's much higher than we could ever acheive in the field. 1.5x more is very common. You will see this when you shoot CS's targets, as his charts have RGB and B&W targets.

In the real world, most color chrome film has an MTF of 40 - 60 lp/mm.... neg film, probably 20% less due to different grain structure.

B&W varies greatly from 60 - 100 lp/mm, excluding Gigabyte film. (I a have not checked the latest version). Please keep in mind, this is the MTF of the film only, its ONE variable in 1/R equation, it does NOT represent the resolution the film can resolve.

For me, I now only shoot color chrome film, occasionaly some color neg.

rvhalejr
14-Jan-2009, 17:22
Amen. :)

rvhalejr
15-Jan-2009, 14:38
... Vacuum Grease...

...largeformatphotography.info/forum/showthread.php?p=1350#post1350



With the large amount of *depth of focus* inherent in large format, I seriously doubt that a vacuum film back would make much of a difference.

rvhalejr
15-Jan-2009, 15:35
I am sorry i can not offer anything else... so, enjoy your journey...

Au contraire .,. :)

...largeformatphotography.info/forum/showthread.php?p=430475#post430475
...largeformatphotography.info/forum/showthread.php?p=430476#post430476
...largeformatphotography.info/forum/showthread.php?p=430476#post430477

Ref post430475 Re: Top-end digital concerns {Intro into Spreadsheet and Plots}

> ... remember, the f #'s and their MP's are MAX. POSSIBLE recorded resolutions, not min. resolutions. This also represents the resolution at the POF (Point of exact Focus). So this assumes you are shooting a FLAT test target or an infinity scene, both having a flat focal plane. When you introduce depth into the equation, the near and far points will always have less resolution than the POF, (up to a point) so the f# and MP's values I offered above, you can cut them by 20 - 50% (estimate) based on the amount of depth you have in a scene. This is why the 568 MP values are so far from reality.... real world depth MP values for 8x10 at f45 can be in the 40 - 90 MP range, based on the amount of depth and f stop used. (more on this below) There has been several web examples of 40 MP digital captures nearly matching 8x10 film - same composure being compared...(color, not B&W) .... and when there is enough depth in the scene the gap can be surprisingly small...but shoot infinity subjects or FLAT subjects, and 8x10 film will destroy a 40 or 60 MP back. This is why the comparisons are all over the map... the devil is always in the details....


When I plot 4x5 @ f22 on a cy/mm vrs. rack and pinion distance (fl = 90mm so x-axis points are roughly at 78, 82, 86, 90, 94, 98, 102mm) I get a wedge shape (it looks like an inverted V, or roof pitch from the side) with the POF being the highest point (maxima and intersectoion of two somewhat straight lines). The line leading up to the POF (at points < 90mm) has a positive slope, The line past the POV (at points > 90mm) has a negative slope described as y=mx+b ...

When I plot 4x5 @ f32 the shape of the wedge becomes flatter due to DoFocus,
Let y'=m'x'+b'

When I plot 4x5 @ f45 the shape of the wedge becomes flatter due to DoFocus,
Let y''=m''x''+b''

and the differences between f22 and f32' and f45'' variables (and b the constant) should generally be ???


>
Here is a simple example that hopefully will bring these numbers into reality.....

We shoot a flat target at f45 with 8x10 color film with 60 lp/mm MTF at the given contrast value of the target. We assume perfect film alignment, focus and diffraction limited lens at f45, single focal plane.... OK?

AT best, we can resolve:

1/(1/33+1/60) = 21 lp/mm

(1500/45 = 33 lp/mm aerial rez)

This means a 30 lp/mm target at the film plane will NOT be resolvable under magnification...it will appear as a blob, vs. cleanly defined lines. It means 20 lp/mm target on the film will appear barely discernible....not a blob, but not sharp. A 10 lp/mm target will look sharp, and a 5 lp/mm target will look razor sharp. This is MTF at work... the finer the detail, the less contrast that is Transfered (hence the T, in MTF) This testing procedure is as old as the hills.... no voodoo math here.



Where does 1/33 come from ???

Where does 1500 come from ???

If we use a three targets:
(1) at near focus (probably near the ground)
(2) in between and to the side (the POF)
(3) at the hyper-focal distance (probably on the top of a light stand) and record three cy/mm values, should this data set (and the plane they define) still be called aerial ???

Thanks before hand,

R. :p (a sign of joy, not disrespect)

bglick
15-Jan-2009, 15:49
> Au contraire .,.

I stopped commented on your mis guided journey..... my posts after that point, were about generic issues... got it?



> I get a wedge shape (it looks like an inverted V, or roof pitch from the side) with the POF being the highest point (maxima and intersectoion of two somewhat straight lines).


This seems to be off from your previous journey, so i will comment. The Depth of focus at the image plane is equal, in front of, and behind the image plane, so perfect wedge is the ALWAYS the resultant plot....... but why plot it? Once you comprehend the definition of DofFocus, its always the same?


> Where does 1/33 come from ???

Your quote above shows where it comes from?? 1500 comes from the avg. wavelengths of light, that determines the MAX. aerial resolution value a lens can project..... 1500 / f stop = max aerial resolution. .... mentioned several times... research "Apt. Diffraction limits" to understand this aspect, again, 100 year old accepted formula, nothing new here either.... It's obvious, after all these posts, you are "now" just starting to investigate 1/R.... ??? carriage in front of the horse? :-)

rvhalejr
16-Jan-2009, 07:42
>
rvhalejr> I get a wedge shape (it looks like an inverted V, or roof pitch from the side) with the POF being the highest point (maxima and intersection of two somewhat straight lines)...

The Depth of focus at the image plane is equal, in front of, and behind the image plane, so perfect wedge is the ALWAYS the resultant plot....... but why plot it? ... :-)

"Complexity is our enemy", differentiation between stops might be enlightening, perhaps second derivatives and the previous question about 3 simultaneous targets .,.

Bummer, I just realized we cannot upload xls files here .,.

rvhalejr
16-Jan-2009, 11:23
...largeformatpro.com/examples_color.html

How many MP ?

Attached is an example of post scan grain reduction
est. image data loss 10&#37; (signal)
est. grain data loss 90% (noise)

Also distributions in sky pre/post

rvhalejr
19-Jan-2009, 13:14
Ref ...pbase.com/bglick/lens_tests

How many MP ?

Attached is an example of noise (grain) measurement as compared to the same area when it is ideally perfect.

This is a first order approximation.

The Original/Idealized under the curve ratio is ==
1/((base e) + (gamma/base e))

Where gamma is 2.2 (Windows) 1.8 (Mac) or 1.4 (some Archival Master Files more or less, the limits for gamma are 2.5 and 1) and base e == 2.71

This example (DSLR) exhibits the ratio similar to the previous Drum Scan example (Over-Scanned at 3200cy/mm yielding 320MP SOP - Standard Operating Procedure) after heavy post-scan processing and noise (grain) reduction.

A better Approximation would have targets in each (film and digital example) with the same cy/mm value.

The same cy/mm (or lp/mm) value is unlikely to be the same so a compensating factor would be used on the film and digital data to normalize.

There is no relationship implied here as to the 1/R, diffraction limits and airy disks as contrasted with the mini-camera-obscura and pinhole modeling of the different film (and digital) formats.

Individual point sampling (in the past) has verified that this method is
similar to the results obtained when calculating the standard deviation,
rms grain values or the generally accepted S/N ratios.

rvhalejr
22-Jan-2009, 08:25
….cityastronomy.com/rez-mag-contrast.htm

Let HRDS == One of the following limits Hale, Rayleigh, Dawes or Sparrow

Hale's Limit (2.71/2) or 1.36 550 • 0.206/D = resolution "arc.
(ex: 1.36 550 • 0.206 == 154.1/127mm= 1.213”arc
Simplified: 154.1/D in mm = resolution "arc or 6.06/D in inches
Rayleigh limit: 1.22 • 550 • 0.206/D = resolution "arc.
(ex: 1.22 • 550 • .206= 138.23/127mm= 1.088"arc)
Simplified: 138/D in mm = resolution "arc or 5.45/D in inches
Dawes Limit: 1.025 • 550 • 0.206/D = resolution "arc
(ex: 1.025 • 550 • 0.206 = 116.13/127 = 0.91"arc
Simplified: 116/D in mm = resolution "arc (or 4.56/D in inches)
Sparrow's Limit: 0.94 • 550 • 0.206/D = resolution "arc
(ex: 0.94 •550 • 0.206= 106.50/127mm= 0.839"arc
Simplified: 107/D in mm = resolution "arc (or 4.2/D in inches)

Where
D == Diameter of telescope mirror
ex: n.nn == period, peak-to-peak or trapezoid (OTDR cats eye) like pulse

Resolving power is the ability of the components of an imaging device to measure the angular separation of the points in an object.

ex: 1.213” == 0 degress 0 minutes 1.213 Seconds

1/60*60*60*1.213 == 3.82um

More: ...microscopy.fsu.edu/primer/anatomy/numaperture.html


ref: ...physics.emory.edu/~weeks/confocal/resolution.html

The best resolution for an optical microscope is about 0.2 microns = 200 nm.

The good news is, there's a difference between resolution and "ability to locate the position".

If you have one tiny and isolated fluorescent object, you can often locate the position of that object to better than your resolution. The image of the object will show up as an extended blob, and you can find the "center of mass" of that blob-shaped image. If the blob is N pixels wide and each pixel is M microns across, you can estimate the center of the blob to about M/N accuracy, which often beats the optical resolution. This is a useful trick, but not solving the same problem as resolution. In some cases you can do various tricks to make the spot size bigger (increase N) so that you can locate the center even better. Various experiments I've heard of have claimed to be able to locate the centers of spots to within 10-30 nm using this sort of method.

rvhalejr
22-Jan-2009, 14:31
Ref ...pbase.com/bglick/lens_tests

How many MP ?
...
This example (DSLR) exhibits the ratio similar to the previous Drum Scan example (Over-Scanned at 3200cy/mm yielding 320MP SOP - Standard Operating Procedure) after heavy post-scan processing and noise (grain) reduction.
...


*** Note: 320MP from 4x5 film == 4000 dpi !!! *** TYYYPPPoooo...
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
(3200 dpi is 200MP from 4x5 SOP)

SNR Noise Reference ...imatest.com/docs/noise.html (Standard Deviation)

The Following Approximates End Product YIELDS for various formats
(DeFocus <= 0 mm; film flatness <= .001 for LF)

Let SNR for 4x5 film = 1/3 (200MP film scan yields about 65MP);
1.75 MP per cm^2 from 3200dpi fluid film scan (10cm x 12.5cm == 125cm^2)
0.58 MP per cm^2 end product yield

Let SNR for 120/220 == 1/2 (33MP/66MP for 645/6x9 yields 16MP/32MP)
1.24 MP per cm^2 from 2800dpi fluid scan
.65 MP per cm^2 end product yield

Let SNR for 35mm film == 2/3 (16MP film scan yields about 12MP)
1.75 MP per cm^2 from 3200dpi fluid film scan
1.24 MP per cm^2 end product yield

=============================================================
See attached Table of Resolution when DeFocus <> 0

1.) An example of how film flatness, precise focusing (with a 35-40x loupe) and
calibration can be important. ref. ...normankoren.com/Tutorials/MTF5.html
for some more uses for loupes .,.

2.) In the table that followed, Lens aberration and resulting
lp/mm values look to be lowfor some quality LF primes that
have good Aberration Balancing.
ref. ...mellesgriot.com/products/optics/fo_6_5.htm

3.) Fairchild Imaging's CCD595 CCD sensor has 85 Megapixels,
9216x9216 8.75 &#181;m pixels; 8.064 cm2 It's designed for aerial
reconnaissance and probably six years old (check the
telescope mirror equations for the size needed to read a
license plate from 250 - 500 miles up on orbit).

4.) Under "Carl Zeiss MTF curves are measured – not just
calculated"

"As far as we can see today Carl Zeiss is still the only
manufacturer to print MTF curves which are measured,
which describe lenses that can actually be purchased,
not just calculated curves of highly ambitious designs
which may exceed the manufacturer's capability of
turning them into reality."
ref ...normankoren.com/Tutorials/MTF2.html#Zeiss

Note: check 120/220 Ziess Lenses .,. (6x7 or 6x9 ?) against Mamiya(s 6x6) .,.

rvhalejr
23-Jan-2009, 14:00
=============================================================
See attached Table of Resolution when DeFocus <> 0


The url to download the spreadsheet is on this page:
...largeformatphotography.info/merklinger-spreadsheet.html


Continuing from the previous post:
ISO 25 4x5 film held very flat and finely focused might yield

Let SNR for 4x5 film = 1/3 (320MP film scan would yield about 107MP);
(10cm x 12.5cm == 125cm^2 for 4x5" film)
(4000dpi == 2.5 MP / cm^2)

2.5 MP per cm^2 from 4000dpi fluid film scan
0.83 MP per cm^2 end product yield

rvhalejr
23-Jan-2009, 14:03
This product is no longer being offered.

Previous customers will continue to receive support.



For Sale:

Loupe and Stands for 4x5 Precision Plenum Photography

Focusing with GG (Ground Glass) is crude and inaccurate.

Offered here is a shimmed plenum and loupe that allows you to verify
that your emulsion plane and focal plane are aligned within .001"
by bringing both into focus simultaneously.

This allows the photographer to validate the camera system and
evaluate details that would not be possible otherwise.

Get the kind of resolution out of your equipment that would make Ansel
Adams cry. Isolate problems, calibrate and utilize equipment at the
highest possible level of performance.

With advances in sheet film scanning (the betterscanning.com fluid
scan film holder of one) you can create high quality 4x5 images that rival
several hundred dollar fluid drum scans.

Using GG is great for composition but almost useless for finely
focused precision photography. Create images reliably and consistantly
that fully exploits the 3200dpi fluid scan resolution with breathtaking
results.

To use the plenum and loupe simply remove the Ground Glass holder.
Once Focused remove the plenum, re-insert the GG and Film Holder
(or 120/220 back) and take the picture.

Satisfaction Guaranteed or Money Back (less shipping)

Pricing Includes Full Documentation and Support

DIY fabrication of the glass and shimming it to the critical dimension.

For normal to near telephoto lenses:
$79.95 for the Loupe (default center of frame stand).

For Wide Angle Angle:
$119 for Loupe and side (of 4x5 frame) stand

$149 for Loupe, side and corner (of 4x5 frame) stand

Ready to go tested shimmed plenums

$49.95 For Glass

$49.95 For Acrylic

Tools for lp/mm Lens Measurement and Profiling
$79.95 for Microscope with Reticule and CS Target.

Transactions will be conducted via ebay and paypal.
Search for "Fine Focusing Loupe" for example listings.
Let me know you saw it here so we can customize your kit.

Shipping is $10, $20 for 4x5 plenums and $30 for 8x10 plenums

Comming soon
$349 4x5 kit with everything for the serious LF photographer
$449 8x10 kit with everything + corner stand (builds on the 4x5 kit)
8x10 plenums are glass only

Still in development
$149 Precision Film Holder (+/- .0005" aligned emulsion plane), USB Black Bag Camera, Documentation and Support

$249 Precision Film Holder (+/- .0005" aligned emulsion plane), Darkroom Night Vision Documentation and Support

$Not Priced yet - Universal upgrade to CCD fluid scanning systems

rvhalejr
26-Jan-2009, 14:21
>
Nate, you correctly point out, all these methods are dependent on film having a single reflective surface. I can assure you, this is not the case. Film is partly transmissive, otherwise rays would not hit the film grain below the surface. So light scatter and light reflectivity can ocur at many depths. I never tested this scientifically, but its just obvious...


The phenomena of disbelief when confronted with irrefutable photographic evidence can be quantified as characteristic of the value believer personality type as opposed to the more impartial scientifically orientated thinking judging type (if memory serves me correctly here).

If any of you ever take the time to look at ALMOST ANY piece of undeveloped film you would find its primary reflection is on the surface (of the emulsion, we do not care about the base which is also reflective).

As far as I know this is totally dependent of the refractive index of gelatin and air (as opposed to the acetate polymer base). When two mediums have the same refractive index there can be no reflection (i.e. when a glass rod is submerged in a fluid of the same refractive index it disappears - I've to a bottle of it around here somewhere from edmund scientific I think, I'd take a picture but that is meaningless to the true believer personality types).

Yes film is a transmissive, and yes sheet glass is transmissive and it also has a very reflective surface when held up to a light source at the appropriate angle.

This is a late correction to this thread and I've been well aware of its inaccuracy since it was first posted. It was intentionally overlooked so as keep the exchange of ideas flowing from which I have benefited as well as (hopefully) others.

I'm still reviewing the thread (and related ones) for useful citations while integrating and synthesizing refined approximations.

rvhalejr
26-Jan-2009, 14:52
This product is no longer being offered.

Previous customers will continue to receive support.

The kit might be offered sometime in the future if some
improvements can be made.,.

This might deserve consideration:

"four images that suggest if the lens is outstanding (a given) and a 40x loupe
used to dial in the peak Point-of-focus behind ideally perfect ground glass (intentionally staying away from plenums here), with a finely calibrated system (another given) and ISO 25 film flat to within .001" AND a tilt angle of not more than 1.5 degrees (I'm admittedly a newb at the very subtle art of tilting)..." A 4000dpi scan might be useful.

...largeformatphotography.info/forum/showthread.php?p=433563#post433563

Loupe Stands and Plenum (in place of GG when focusing with 35-40x Loupe)
...largeformatphotography.info/forum/showthread.php?p=423824#post423824

Wixey Digital Angle Gauge accurate to within +/- .5 degrees (for tilt angle)
...largeformatphotography.info/forum/showthread.php?p=429219#post429219

rvhalejr
31-Jan-2009, 20:21
The kit might be offered sometime in the future if some
improvements can be made.,.


Tilt Tool Update (...tiltmeter.com/DIGITALMODEL.html)
RESOLUTION: 0.1 DEGREES
REPEATABILITY: +/-0.1 DEGREES
$44.00 Model# EDG
PORTABLE. DIGITAL INCLINOMETER.

LF Film Flatness
Not recognized as an issue with most LF practitioners. Counter-intuitive to SLR and MF photographers as the softness on film and scans is very obvious in the smaller film formats.

LF practitioners will intentionally defocus (when using tilts) and use small apertures to bring near objects into better focus as a Standard Operating Procedure (SOP).

The tendancy to defocus is much more prevalent with view cameras as opposed to press cameras, photographing planar (flat Ariel) or copy artwork.

So scanning at 3200dpi can be considered to high by view camera operators that may in fact defocus often (using tilts and small apertures which defocus in the image plane).

Scanning at 4000dpi where slr and mf film flatness can be directly observed is unheard of in LF photography.

LF view camera practitioners can believe that if an instrument is not provided by an OEM then it has no utility. Exceptions to this rule may be betterscanning.com, zig-align.com, gretagmacbeth.com, imatest.com, etc.

ref: ...zig-align.com
"follow the basic rule of test and measurement – to check with ten times more accuracy than you need to achieve" ref zig-align.com Hence the 35-40x loupe as a intuitively useful instrument (which some would rather burn in hell than try to use).

ref: ...zig-align.com/advanced.html
The Ring Module (Optical Flatness Measuring device) will check flatness to .001" or better (what I've been looking for) hint: remember the original practice plenum shims, might yield more parallelism (front and back standard calibration) utility.

Testing with newton's rings (an unwanted flatness artifact) may also be useful here (its worthy of a look although probably much smaller than what is needed here). Remember that most here never grasped why the dial indicator was not reliable. That and when they buy $20K worth of sheet film it all seems to be (no big surprise) all flat.

Its just this poster (who buys a box at a time) who has any film flatness problems.,.

Sigh.,.

bglick
31-Jan-2009, 23:18
> Scanning at 4000dpi where slr and mf film flatness can be directly observed is unheard of in LF photography.


It's not unheard of, its based on the film type used, the f stop used and the depth of the subject.... and of course, the obvious issue, how large is the intended output.



> LF view camera practitioners can believe that if an instrument is not provided by an OEM then it has no utility. Exceptions to this rule may be betterscanning.com, zig-align.com, gretagmacbeth.com, imatest.com, etc.


This is a ridiculous stretch.... since view camera makers do not include exposure meters, does this mean they do not recommend people use them? Of course not. But OTOH, this does not mean every accessory in the world is applicable to every view camera, which is the assertion you are trying to make.


As for Zig Align, this product is designed to square the subject plane with front and rear standard. It has NOTHING to do with your intent of pursuing gg and film alignment to .001". You are comparing apples and bananas. Not even close. Not to mention once again, this is an issue with "COPY WORK ONLY", not general photography.... i still think you have not swallowed this ugly pill.... as you never denote such.... you tend to treat copy work and landscape photography all the same...



> Hence the 35-40x loupe as a intuitively useful instrument (which some would rather burn in hell than try to use).


I assume that must be me burning in hell.... As I mentioned at least 4x in the past.... I own loupes from 2x to 125x..... they are all useful tools, WHEN USED IN THE RIGHT APPLICATION. A 40x loupe by itself is nothing magical. You seem to think it is.


Viewing through a plenum on the back of standard with the gg removed is NOT an accurate way to accomplish your goal. Their is several reasons for this....the most important one that comes to mind is, without knowing the EXACT back focal distance of the loupe itself (which is never published) when you bring the loupe to focus, there is no way to ascertain where the loupes plane of focus lies, in relationship to the plenum. In addition, most loupes which are focusable will have a shift in image plane position. The same is true when a loupe is zoomed. So while you have the loupe in sharp focus, it offers no meaningful information as it relates to film and gg alignment, as you simply do not know where the loupes image plane lies. All you have accomplished is, you have the lens aerial image in focus.....but not your intended goal of knowing where the lenses image planes lies.... understand? ?


Another problem with using a loupe at the image plane for alignment is light fall off.... if you plan to use a lens at f32, you should not test it at f5.6 with a loupe, as when you stop down, the image plane will shift. However, f32 does not allow sufficient light to properly assess targets, as the eyes MTF is so poor at these VERY low light levels....therefore, you are negating the value of the magnification.


As I stated since you are started this thread, you are introducing new variables which can not be accurately controlled. Hence the simplicity of accuracy of a dial indicator test with some good straight edges. This simple hardware test does NOT have any of the optical variables you are introducing, making the hardware test waaay more accurate and repeatable than your optical methodology. You continue to over-complicate a very simple procedure....and in the process, you will generate mis-leading results.


Of course, the simplest and lowest cost procedure is to shoot a few pieces of film. Make slight focus variances and record these differences using a dial indicator. You can easily tell if film and gg is out of alignment ... the focus align target product discussed earlier also works well with this. Out of focus errors are very obvious. But once again, all of this only significant for "copy work", not for a depth shot, such as your dream Ansel Adams Yosemite shot, which is how you started this thread, remember?



> The Ring Module (Optical Flatness Measuring device) will check flatness to .001" or better (what I've been looking for) hint: remember the original practice plenum shims, might yield more parallelism (front and back standard calibration) utility.


Yep, all this is true, when used in the application it was intended for, for copy work, or aligning enlargers. The goal is, to be assured the 3 critical planes are parallel to each other. This has NO relationship to your original goal of gg/ film alignment. As you know, an enlarger has no viewing ground glass, so once again, your analogy is meaningless as it relates to your goal.



> Remember that most here never grasped why the dial indicator was not reliable. That and when they buy $20K worth of sheet film it all seems to be (no big surprise) all flat.


Yes, I still don't grasp why the dial indicator is not reliable. Why don't you explain this in detail??? This should be very interesting. Also, you keep harping on the film not laying flat on a flat surface.... all I am concerned about is how flat the film is inside the holder. All my film holders have very tight slots on all 3 slides... this forces the film flat. Once again, with a decent depth dial indicator, and a pair of 3x - 5x eye glasses, ($8) you can measure film buckle IN THE FILM HOLDER, VERY ACCURATELY! You will see the errors are so tiny vs. the Depth of Focus at the film plane.... it's not worth discussing. Of course, if you have 1800's film holders, or possibly defective film holders, this might be a problem, but it will become very obvious with this simple test....


It is becoming evident, that no matter how much logic is thrown your way, you are hell bent on implementing your methodology.... it seems you started with an idea, and you simply can not move off-base.... i think its important to keep these threads with as much factual information as possible. None of this is personal against you. As I mentioned previously, optics is tricky, its easy to be fooled...

rvhalejr
3-Feb-2009, 19:53
> ....it's not worth discussing...


I've run out of time and would rather you did not spend any more time here either.

The notes, references and ideas that I continue to post are intended to help revisit the 4x5 Ultra Fine Focusing and Calibration endeavor at some point in the future when time (hopefully) permits.

Sadly, as was recently pointed out to me, some experts have passed on and are no longer with us. Hopefully they have left behind enough bread crumbs for others to pick up where they left off. I've been trying to do the same, tickling the imagination, knowing that reasonable minds will differ while trying not to mislead or offend.



... it seems you started with an idea, and you simply can not move off-base.... i think its important to keep these threads with as much factual information as possible. None of this is personal against you. As I mentioned previously, optics is tricky, its easy to be fooled...

I'd love to collaborate with you but thats probably never really been in the cards.

For one thing, establishing a common baseline reference is arguably boring as hell. Simple things like cross-checking our dimensional characterization of film, mailing our measured sheets to each other and then comparing notes would mean a lot, if we ever get the time.

But time is the enemy of all men, so it would be prudent to get out there and do what you love while you can, taking really big pictures and making really big prints (without any noise - amazing).

It looks like one of your shots is of El Capitan using a bit of tilt up (I do not even own a view camera so I could be wrong). But the most amazing piece of Granite in the park arguably is Cactus Rock (which even AA may have never shot) on the rim as seen to the west of the shopping center store parking lot. Its something that should not exist, but it does and only those careful and persistent enough will ever see it (sadly to many see but never really see).,.

Looks like AA and QT Luong missed it (...terragalleria.com/parks/np.yosemite.all.html)
and (sigh) I cannot seem to find a shot of it anywhere on the web .,. so your going to need to go on faith that it does exist (or maybe call the park service and have a chat with the principle geologist or senior ranger).

Get that one and you will be a Yosemite rock star. To do it justice you may need to use the DSLR, MF and/or LF to find out what is best for a really big print.

Getting **THE** shot of a natural phenomena most (if not all) of the experts missed (and should not exist in a glaciated granite valley) might arguably delineate the best of all the greats.

The down side is that to get a great LF shot you may need to be inside a park service helicopter about 200 feet from the subject at an altitude of 3,000 ft from the valley floor, using fast film and a shutter speed of 1/500th of a sec to cut down on the vibration (an old 4x5 press camera might work).

You could get a little blue sky in the frame to show that there was no noise (or grain) as that seems to be your signature style.

But then again, its just another dream, getting a shot of a rare (one out of a million) anomaly that so many other great photographers (and millions of visitors) seem to have missed .,. :p

bglick
3-Feb-2009, 22:24
> I'd love to collaborate with you but thats probably never really been in the cards.


It's always been "in the cards".....but to collaborate, you must respond to questions when asked, and that was never the case with you. I sure tried....


Now, who passed on? Why the secrecy?

rvhalejr
4-Feb-2009, 18:09
In another life I worked on a project called the Hubble Space Telescope. No way
would NASA allow us to open up the roof and check the optics because they
knew better. So it went up on orbit and could not focus on a damn thing.

I WILL NEVER BE PUT THAT POSITION AGAIN !!!



From: Astronomical Optics {Jon Holtzman 2008-08-2}
Ref ...ganymede.nmsu.edu/holtz/a535/ay535notes/node29.html
Physical (diffraction) optics


"A wonderful example of the application of all of this stuff was in the diagnosis of spherical aberration in the Hubble Space Telescope, which has been corrected in subsequent instruments in the telescope, which introduce spherical aberration of the opposite sign. To perform this correction, however, required and accurate understanding of the amplitude of the aberration. This was derived from analysis of on-orbit images.

Note that it is possible in some cases to try to recover the phase errors from analysis of images. This is called phase retrieval. There are several ways of trying to do this, some of which are complex, so we won't go into them, but it's good to know that it is possible. But an accurate amplitude of spherical aberration was derived from these images.

This derived value was later found to correspond almost exactly to the error expected from an error which was made in the testing facility for the HST primary mirror, and the agreement of these two values allowed the construction of new corrective optics to proceed... "


Ref ...ganymede.nmsu.edu/holtz/a535/ay535notes/node37.html
Field Flatteners


"As we've discussed, all standard two-mirror telescopes have curved focal planes. It is possible to make a simple lens to correct the field curvature. We know that a plane-parallel plate will shift an image laterally, depending on the thickness of the plate. If we don't want to affect the image quality, only the location, we want the correcting element to be located near the focal plane.

Consequently, we can put a lens right near the telescope focal plane to flatten the field. For a field which curves towards the secondary mirror, one finds that the correct shape to flatten the field is just a plano-concave lens with the curved side towards the secondary. Often, the field flattener is incorporated into a detector dewar as the dewar window."



The 4x5 View Camera's Fresnel functions as a concave field flattener, with the angle of each concentric focusing element varying from 90 degrees at the center of the image plane, then about 75 degrees on the side, then to about 65 degrees in the corners (using the approximate 35-40x loupe tilt angles needed to use with a 90mm 4x5 Schneider Angulon Lens).

In other words, these angles correspond to the central normal plane vector (at a perpendicular 90 degrees) to increasingly tangential in the corners (to about 65 degrees) and describe the Line-of-Sight (or a bore-sight collimated ) vector from the image plane to the aperture (entrance pupil).

This is why a loupe only works in the center of the ground glass without being tilted as it is positioned on the sides or corners, a result of the field curvature of the Lens Makers formula which does not model (in this example) the image plane as well as the Fresnel model.

To keep the example simple the radial (x,y) coordinates have been ignored but the loupe must be pointed at the entrance pupil in order to focus (as well as having the correct 90-75-65 degree tilt in the z axis).

Its painful to set this up so having one loupe dedicated to the center, side and corner of frame saves a lot of tinkering time. Outlining the position of the inclined stands on the back of the plenum would also help a lot.

bglick
4-Feb-2009, 18:32
I never did grasp how the failed NASA Hubble telescope relates to taking photographs with a view camera. In some twisted way, you seem to think that both optical instruments have the same level of complexity?

I also do not understand why you are quoting the use of a field flattner between a telescopes objectives lens and its Eye Piece (EP).....you seem to write posts without conveying a message, you just start quoting stuff? I can only guess, you are drawing some parallels between the telescope and the view camera?

Objective lenses are have field curvature, which is often corrected with telescopic Eye Pieces. When the scope is used for astrophotography, and no EP is used, the field flattner corrects the curved field at the image plane to so the image plane is close to the recording media plane. How does this relate to view cameras? All view camera lenses project FLAT images, as they are NOT both visual and photographic instruments.....



> This is why a loupe only works in the center of the ground glass


Works for what? In previous discussions you mentioned NO ground glass, just plenum and loupe, i.e. direct rays from lens to loupe. Now, we are back on the ground glass? I don't follow your post, what is the point you are trying to make?

Nathan Potter
4-Feb-2009, 20:36
rvhalejr' I can't follow all your stuff above about the Hubble, and as with bglick I'm confused about the relevance to a view camera focusing method.

I would comment that a loupe functions best when its' optical axis is aligned to the optical axis of the view camera lens; that is both axes are colinear. Under such conditions the loupe collects the maximum number of scattered rays from the GG. You pointed this out.

The loupe becomes increasingly deficient in collecting rays that are off its' optical axis - which is the case as one moves away from the center of the GG. This effect can be mitigated somewhat by using an apparatus which rotates the loupe optical axis off 90 degrees from the GG and toward the direction from which the ray bundle originates. That is to say put the loupe on a swivel and supply it with a focus mechanism for use away from the center of the image. Even with such a fixture the optical axis of the loupe will be at an angle to the GG so you'll capture a sharp focus at only a single line within the field of view, but there will be a considerable gain in the image brightness, and I think you'll be surprised at the critical focusing advantage.

You may want to think about the swivel apparatus idea and maybe find a design to implement it rather than your current approach of a dedicated off axis approach.

Nate Potter, Austin TX.

rvhalejr
5-Feb-2009, 16:42
rvhalejr' I can't follow all your stuff above about the Hubble, and as with bglick I'm confused about the relevance to a view camera focusing method.

The principle revelation should be that testing is a good thing. Secondly Press Cameras, VIEW Cameras, ULF, MF, DSLR, Microscopes, Telescopes, tilt and lens maker formulas AND the lowly camera-obscura have some similarities while being totally different if not arguably unique in functionality.

AND do not assume this even scratches the surface (i.e. ISO 25 film above 6,000ft and the Alpine lake subject @ 4000dpi scan, one out of 10,000, photon scatter, etc., )

When I started this thread it should have been clear that I was using a little optical system (Loupe or small Microscope) to DRILL DOWN into the focusing of the 4x5 camera. Just like a Spotting Scope is useful to help out a Telescope perhaps some might find utility in a bigger loupe than is normally used with a 4x5 PRESS or VIEW CAMERA.



I would comment that a loupe functions best when its' optical axis is aligned to the optical axis of the view camera lens; that is both axes are colinear. Under such conditions the loupe collects the maximum number of scattered rays from the GG. You pointed this out.

The loupe becomes increasingly deficient in collecting rays that are off its' optical axis - which is the case as one moves away from the center of the GG. This effect can be mitigated somewhat by using an apparatus which rotates the loupe optical axis off 90 degrees from the GG and toward the direction from which the ray bundle originates. That is to say put the loupe on a swivel and supply it with a focus mechanism for use away from the center of the image. Even with such a fixture the optical axis of the loupe will be at an angle to the GG so you'll capture a sharp focus at only a single line within the field of view, but there will be a considerable gain in the image brightness, and I think you'll be surprised at the critical focusing advantage.


I don't have time for this as I've got to move soon and there are some other matters that demand my time.

You have a good grasp of the ray bundle. But observation clearly contradicts your "only a single line" assumption at working apertures. That MAY be observable at wider apertures (f2.8) and at higher magnification (>=100x) but not in the 4x5 camera working range.

In addition to the swivel apparatus there would need to be typical microscope rack and pinion travel of 1-2" as when the stands tilt they must be moved closer to the image plane to maintain the same focal distance.



You may want to think about the swivel apparatus idea and maybe find a design to implement it rather than your current approach of a dedicated off axis approach.

Dedicated off-axis == cheaper and faster as 35-40X is a practical limit. The dedicated stands are difficult and dangerous to fabricate, which I probably will not do again.

Yes Swivel/Rack and Pinion are the tried and true microscope design !!!
Sadly, there is not enough volume to justify investing in that, nor does there seem to be a good one off the shelf (unless you go whole hog with a real 40x microscope and stand, about $1K, maybe less now).

But it will do no better results behind GG than a 4-6x loupe. Its got to be air or clear for Ultra Fine Focusing.

Bless his heart, but I did not want to tell BG that I use a table saw and belt sander to fabricate the stands and that he should do the same (ugh awful idea), I'd rather mail him (or you) a kit from stock on hand than wasting his (or your) time in the shop.

When you done your can send it back or whatever. Plenums used to be my biggest headache, then the dedicated stands. I think marking the back of the plenum for near-far-mid field distances (and radial orientation) would be another time saving step (unless all you do is measure lenses all day long, which 35-40x is not that great at any way).

The other thing you will never understand unless you try it is that once the plenum surface matches the same distance as the emulsion layer (in the holder) you can put the emulsion layer of a piece of developed film against the plenum and focus on the IMAGE AND THE EMULSION LAYER simultaneously.

I no longer have time for this (honestly) but if any significant poster(s) here what to eval the kit let me know. My interest is in what the technique can do in the hands of accomplished LF practitioners.

P.S.
The deal with the dial indicator is that the probe may deform the film during measurement. As a practical matter we can do the measurement (range) by using the conventional helical adjustable height gauge gauge. When the dial deflects we then slide over the surface plate (rock slab) and determine the height using rung gauge blocks (not the stuff in the kit for rough measurement). The heights of deflection and non-deflection would be statistically analyzed and normalized to approximate the distance a non-touching instrument would yield (optical refractometer i think).

R.

bglick
5-Feb-2009, 17:38
> But it will do no better results behind GG than a 4-6x loupe. Its got to be air or clear for Ultra Fine Focusing.


Now we are back to focusing the aerial rays of the lens.... and I assume (since you never comment on it) the intended use is still depth shots, such as your landscapes..... not flat plane photography, such as copy work.. Its obvious all this correspondence has not convinced you of anything..... but to close out the thread, once again, I will repeat the 3 primary reasons why this makes no practical sense:


1) You have no idea what the back focal distance of the loupe is. Without this information, all you can do is bring a given part of the scene into focus, but you will have no idea where that focal plane lies....remember, you looking for .001" accuracies, whereas this one item alone will have about 5 - 10x this error, maybe more based on the loupe design.


2) Even if you did nail focus at a given point in the scene, what's the benefit? At f32, if you mis focussed by 20% or so in the scene, it will simply shift the DOF a small bit, not even noticeable in the final image. Regardless, Depth of Focus at the film plane will account for this errors...


3) The ability to focus the avg. view camera is so sloppy vs. the levels of accuracies you are trying to attain for gg / film alignment, it makes no sense. If you test your ability to focus on a scene, on the same object, using a dial indicator on the standard that is used for focusing, you will see, its impossible to consistently focus within .005".... so why shoot for .001" for film plane alignment? Get it? This has been tested many times...focus on a view camera is a very sloppy process. This is not laboratory gear. Many view camera focuser's are so crude, you could never repeat .01" focus positions on the same subject in repeat attempts. It's all about the weakest link in the chain, and there is so many of them, that to attack ONE link, and try to tackle down to ultra critical accuracies will not benefit the end product.


Your position about the dial indicator on the film is not accurate. If you use a flat bottom plunger on the dial indicator, you will NEVER deform the film, unless you apply hundreds of pounds of pressure, but who would do that? With a bright light, some 5x specs, you plunge till you hit the film, evident by the change in light pattern on the film, continue plunging till the plunger stops, the difference is your film buckle. this can be accurate within a few thous.... how much more accurate do you need it?


> The principle revelation should be that testing is a good thing. (Hubble issue)

Yes, it can be.... but the Hubble was the first of its kind, and was never tested. View cameras have been around 150+ years, and have been tested to death, so its the analogy that many of us don't get.


I have continued to applauded your tenacity for attacking this issue.... but without a solid understanding of the fundamentals of what you are testing, you can easily perform tests that give no meaningful results.... please don't take offense, this is very common in the field of optics..... even optical engineers get fooled often. Hence why, whenever I enter unchartered optical waters, I always double and triple check with as many people as possible. In optics, you must be humble.... As I mentioned, I work with many optical engineers, and its amazing how they correct each other, lay people catch them on errors, etc.

rvhalejr
5-Feb-2009, 21:15
> I will repeat the 3 primary reasons why this makes no practical sense:

1) You have no idea what the back focal distance of the loupe is. Without this information, all you can do is bring a given part of the scene into focus, but you will have no idea where that focal plane lies....remember, you looking for .001" accuracies, whereas this one item alone will have about 5 - 10x this error, maybe more based on the loupe design.


A lot of work went into destructive examination and analysis of the loupe. So the value is easy to get (If memory serves me correctly). The off brand loupe has the same FL as the Carson (which is in the name, I think). Anyway, they both work the same but my sense is focal length or not, disparagement is all that I can expect here.

At this point the .001" accuracy bitching is starting to sound like that of a well paid industry lobbyist or consultant.


>
2) Even if you did nail focus at a given point in the scene, what's the benefit? At f32, if you mis focussed by 20% or so in the scene, it will simply shift the DOF a small bit, not even noticeable in the final image. Regardless, Depth of Focus at the film plane will account for this errors...


As a 4x5 Press Camera user one would like to control all variables save the one thats of interest, with everything in focus at infinity DOF can be ignored, DoFocus at the film plane can be == to the emulsion plane (about .001" if one happens to read data sheets and/or deconstructs film under a 400x microscope).

Why does everything 4x5 have to be strictly DOF and DoFocus with you ??? Why not grasp that they may not always be of paramount importance beyond your view camera ? Please refrain from answering the rhetorical questions, Get it ???


>
3) The ability to focus the avg. view camera is so sloppy vs. the levels of accuracies you are trying to attain for gg / film alignment, it makes no sense. If you test your ability to focus on a scene, on the same object, using a dial indicator on the standard that is used for focusing, you will see, its impossible to consistently focus within .005".... so why shoot for .001" for film plane alignment? Get it?


Your argument IMHO is a stretch w.r.t. test and measurement best practices.

There are at least two references to support this (at least one from Zeiss and someone else if I recall) that you are ignoring. Why is it beyond the pale to think that an curious engineer might want 10x over the resolution to make a critical measurement (that will LIKELY draw a lot of negative comment).

Get it ??? Your 4x LF loupe time 10x == 40x AND the only time I cannot hold .005" with a helical or rack & pinion is never !!! *** ITS A MICROSCOPE FOCUSING MECHANISM *** Ever use one ??? Please refrain from answering the rhetorical questions, Get it ???


>
This has been tested many times...focus on a view camera is a very sloppy process. This is not laboratory gear. Many view camera focuser's are so crude, you could never repeat .01" focus positions on the same subject in repeat attempts. It's all about the weakest link in the chain, and there is so many of them, that to attack ONE link, and try to tackle down to ultra critical accuracies will not benefit the end product.


I've always specified ***CLEARLY*** that one needs helical or the rack and pinion mechanism. Over and Over and Over again, but thats not going to work here. This is an example of how "Critical Design Review" became a dreaded engineering concept.
Please refrain from replying to generally accepted practices and principles, Get it ???


>
Your position about the dial indicator on the film is not accurate. If you use a flat bottom plunger on the dial indicator, you will NEVER deform the film, unless you apply hundreds of pounds of pressure, but who would do that? With a bright light, some 5x specs, you plunge till you hit the film, evident by the change in light pattern on the film, continue plunging till the plunger stops, the difference is your film buckle. this can be accurate within a few thous.... how much more accurate do you need it?


I've been talking grams (more like fractions thereof) !!!
Are we DENSE or what ??? Please refrain from answering the rhetorical questions, Get it ???

Not many Professionals in Test and Measurement would confuse a DUROMETER measurement (foot pounds or newtons) with the distributed force (of the acetate base and gelatin emulsion with different affinities for humidity) which i suppose causes sheet film to bulge (yes that is a hypothesis based on test results).

I have given you pictures of this and explained it over and over again: Its micro-grams NOT POUNDS !!!


> The principle revelation should be that testing is a good thing. (Hubble issue)



Yes, it can be.... but the Hubble was the first of its kind, and was never tested. View cameras have been around 150+ years, and have been tested to death, so its the analogy that many of us don't get.


Its given that you have the inside scoop on View Camera optics.

However consider (if one can) Hubble used the Hale telescope (which I own and designed according to you) and on it is a little tiny spotting scope (arguably, which Galileo would recognise how to use).

Whats the connection, besides the time that has passed between Newton and now, other than a history citation validates your brittle view camera beliefs and values ???
Perhaps many of us don't want any of that (much less get it).



I have continued to applauded your tenacity for attacking this issue.... but without a solid understanding of the fundamentals of what you are testing, you can easily perform tests that give no meaningful results.... please don't take offense, this is very common in the field of optics..... even optical engineers get fooled often. Hence why, whenever I enter uncharted optical waters, I always double and triple check with as many people as possible.


"Performing tests that give no meaningful results..." Obviously the management opinion that sent a 3 billion dollar piece of gear up on orbit that could not Focus THE HUBBLE GOT IT ??? !!! BRAVO !!! and now lets burn her up !!!!!!!!!!!!! Yeeee-Hawwwww !!!

You would never know that there are those (like myself) out there that are Microscope, 4x5 Press Camera and Telescope practitioners, who do indeed count photons and find the unbiased scientific method useful.



In optics, you must be humble.... As I mentioned, I work with many optical engineers, and its amazing how they correct each other, lay people catch them on errors, etc.

Please don't take offense, but I will no longer apologize for EVER thinking this could be a venue where the opinion of optical engineers and LF practitioners might be sought and opinion unbiasedly given.

This entire exercise was about trying to explain why the 4x5 Press (not screw[less ?] View Cameras) that do not, under some conditions, produce an end product up to expectation.

BRAVO. Nice work.

R.

bglick
5-Feb-2009, 22:26
> The off brand loupe has the same FL as the Carson (which is in the name, I think). Anyway, they both work the same but my sense is focal length or not, disparagement is all that I can expect here.


Rich, its the "back" fl of the loupe, not the "fl". The BFL represents the problem....the back fl is the distance from the bottom element where the image comes into focus. When using a loupe to view and aerial image, unless you know exactly where the focal plane is on the loupe, then it does not serve your purpose? That is the reason you are using the loupe, right? When you focus on a gg or film on light box, you know exactly where the back focal plane is.... but not with an aerial image.... make sense now?


Your method would work if you used a 3 micron fiber optic plate as your ground glass, then you would surely know where the back focal plane lies... while still resolving the aerial image. The the fiber optic plate will give you an image almost as sharp as a direct aerial reading...





> At this point the .001" accuracy bitching is starting to sound like that of a well paid industry lobbyist or consultant.


or.... someone trying to help?



>Why does everything 4x5 have to be strictly DOF and DoFocus with you ???


AS I mentioned all throughout the thread..... when doing copy work, and using lenses designed at wide apt., such as enlarging lenses, your quest takes on some credence....but this thread started by you shooting scenes in Yosemite, and you never pushed the thread into copy work..... so it is all about DOF and Depth of Focus. Even at infinity, you will still use a lens at it's optimized f stops, because your entire thread is about maximizing resolution......and at these f stops, they provide sufficient Depth of Focus...



>There are at least two references to support this (at least one from Zeiss and someone else if I recall) that you are ignoring.


Zeiss? f32? Not that i ever read. Zeiss at f4, yep, they take film flatness very seriously, and they should....

Anyway, i can't respond to much else, cause I simply do not understand what you write.... so, ..... I surrender ..... white flag raised..... I am sorry my posts upset you, that was never my goal...

rvhalejr
6-Feb-2009, 15:37
rvhalejr> The off brand loupe has the same FL as the Carson (which is in the name, I think). Anyway, they both work the same but my sense is focal length or not, disparagement is all that I can expect here.




Rich, its the "back" fl of the loupe, not the "fl". The BFL represents the problem....the back fl is the distance from the bottom element where the image comes into focus. When using a loupe to view and aerial image, unless you know exactly where the focal plane is on the loupe, then it does not serve your purpose? That is the reason you are using the loupe, right? When you focus on a gg or film on light box, you know exactly where the back focal plane is.... but not with an aerial image.... make sense now?


Thank You for a better problem definition. If I'm not mistaken a simple BFL math model
can be had here Ref: ..answers.com/topic/lens-1 (to model the issue at hand)

This is confusing me: "When you focus on a gg or film on light box, you know exactly where the back focal plane is.... but not with an aerial image...."

The 35-40x Loupe is actually a three element pocket microscope system with one course and one fine helical adjustment. It is typically used to examine film on light box and/or film on a glass slide or film on a plenum (4x5 piece of glass with the back surface in the same plane as the gg and/or Filmholder+Base+emulsion).

The 4x5 Projects an Image into the gg and/or emulsion plane. So when we integrate the 4x5 system and microscope system in a manner in which they were designed, and knowing this has been done before and there does not appear anything in the BFL math model or theory of operation to stand in our way of my tinkering technique,
what am I missing ?

With the three element pocket microscope (35-40x Loupe) I cannot find any references that imply there is any problem with an aerial image (since a microscope does not always need to use immersion oil, especially at low magnification).

So I'm stumped...(this is very frustrating)...



Your method would work if you used a 3 micron fiber optic plate as your ground glass, then you would surely know where the back focal plane lies... while still resolving the aerial image. The the fiber optic plate will give you an image almost as sharp as a direct aerial reading...


Bob, your Bee image and 90 degree light pipe not only confused me but left a dubious impression as to its authenticity, if it came from corning then it is probably valid, they are well aware of the minimum bend radius limit thats specified (used to be about a 3 foot diameter) without damaging the cladding or fracturing the glass. Perhaps it was (is) a molded glass element but most fiber optic engineers I've met over the years would end up rolling around on the ground laughing (and/or spirting beer and wine out their nose).

You did indicate that you saw one (i think) so it probably works although i would like to examine it under the microscope for any lensing and/or orientation of the light pipes. Its the fixation on the "How does it work" thing.

I know exactly (within .001") of where the back focal plane is for the 4x5 because its in a very specific position (great pains have been taken to measure and statistically analyze to match up with given set of film holders and brand of film). The ideal Film Holder+Base+Emulsion dimension gets a a lot of my attention, which I refer to as the CRITICAL DIMENSION and go to greats lengths to discuss and sketch, etc.

The back focal distance of the microscope can be had but I'm not sure what it gets us (If I have not documented I'll remeasure if needed) and I think the eye relief is known. I've mentioned 35-40x because on the no-name its about 37x (calculated) and the carson a bit higher. The FOV and Front FL is also known.

So I'm stuck yet again... What am I missing ?



rvhalejr> At this point the .001" accuracy bitching is starting to sound like that of a well paid industry lobbyist or consultant.




or.... someone trying to help?


Thanks, but my lease is up and I've got to find a new place to rent, hence the urgency to put this thing to bed (for now). If there is a known problem that I'm not grasping I need to know ASAP as there are people out there depending on the Microscope in the Emulsion Plane technique AND I've promised them support.


rvhalejr>
>Why does everything 4x5 have to be strictly DOF and DoFocus with you ???




AS I mentioned all throughout the thread..... when doing copy work, and using lenses designed at wide apt., such as enlarging lenses, your quest takes on some credence....but this thread started by you shooting scenes in Yosemite, and you never pushed the thread into copy work..... so it is all about DOF and Depth of Focus. Even at infinity, you will still use a lens at it's optimized f stops, because your entire thread is about maximizing resolution......and at these f stops, they provide sufficient Depth of Focus...


Another Mis-communication... By "copy art work" I meant shooting hi-res true color
of very expensive paintings (2d) and product photography (the bigger the more 3d).
Yosemite is part of the mix, as is architectural and portraiture. So its E6, B&W and C41 with attention paid to High Res, DOF and Diffusuion (with the later being the most sophisticated, difficult and challenging to practice well).


rvhalejr>
There are at least two references to support this (at least one from Zeiss and someone else if I recall) that you are ignoring.




Zeiss? f32? Not that i ever read. Zeiss at f4, yep, they take film flatness very seriously, and they should....


Can't I have a little different artistic opinion on this ? Conventional LF Best Practices and well understood Models aside (much of which we both agree with)? I recently got proved wrong (arguably more like old persons memory failing) about f32 getting some really sweet DIFFUSION. So once all the dust settles I'd like to fine tune want I consider to be a very subtle and sophisticated technique which is usually (IMHO) easy to over do (hence the big-o-loupe and f32).

I'm a NewB tinkering tilter, so I might try to sneak in a little tilt to bring near DOF in a little better and determine the optimal point of focus somewhere between f16 and f32.

So can you try not to beat me over the head about how "film flatness" at f32 is totally useless ? Thank You before hand (we both agree there a limits as to its efficacy depending on f-stop size). I've got on the gear to play in the "film flatness" sandbox now but its going to have to wait because of the move.



Anyway, i can't respond to much else, cause I simply do not understand what you write.... so, ..... I surrender ..... white flag raised..... I am sorry my posts upset you, that was never my goal...

Hopefully where I'm stuck is clear (at least in this post). Thanks for the white flag, this is in the "New Products" place so we need to be mindful of sensitivities. I will try to focus better on the LF fine focusing issues at hand (Especially what I'm stuck on).

I'm facing a HORRIBLE move, every time I do that it takes a year to sort out where all the gear and archived stuff got put, So I'm old AND Cranky right now.

You have spent a lot of time here so anytime you want to tinker in the LF big-o-loupe sandbox let me know, there is PLENTY of room. Who knows, after I come back from the move you may have figured out some cool stuff.

R.

rvhalejr
6-Feb-2009, 17:15
FYI: More discussion on Aerial focusing

"In Answel Adams' book, The Camera, he says that you can drill small holes in the ground glass, and put a small fine wire across each hole on the ground side. Focusing on that wire with a magnifyer, he says that you can focus on the aerial image with maximum resolution/clarity."

Ref ...largeformatphotography.info/forum/showthread.php?p=433645

Parallax Focusing (Noding Yes & No with head)

Ref ...photo.net/bboard/q-and-a-fetch-msg?msg_id=000ukR

bglick
7-Feb-2009, 09:24
Rich, since you entering into a "move", you have a right to be cranky.... I too struggle with moving...it takes me forever to get back on track... so best of luck to you....

to make your move more peaceful, I pulled down the white surrender flag to put you mind at ease on the issue you raised....

First, the goal continues to change through-out the thread, from aerial focusing, to aerial focusing for the intent of improving film / gg alignment. You never seem to designate when you refer to one, vs. the other..... but no need to re-hash, I will address your aerial focus issue.

I am glad you found that Ansel Adams reference..... It will save me along explanation of the problem. It's no surprise that Ansel came up with a very eloquent solution for the problem I presented to you. If you place a wire over drilled holes in the ground glass, and you focus the loupe on the front of wire (not easy since light is coming from the other direction), you will eliminate the back fl (BFL) potential error. This will eliminate your eye accomodation focus setting as a variable.


So this technique would be effective. Although you still can't place the focal plane within .001", due to the combination of the DOF (Depth of Field) of the loupe which is at least .01" or more, and the Depth of Focus of the image plane, based on f stop.... these two planes create an overlap zone of sharp focus, where your eye could never discern the difference within this plane. But for focusing purposes, (not alignment) the .001" figure is so ridiculous. Without going through all the variables, if you achieved 50x this, or .05", this level of focus placement is beyond superb...

So to be clear, this technique is not effective for gg/film alignment, but for photographing flat objects it might be helpful to assure you are at the point of best focus. I say "might" because a well aligned gg/film plane and a 4x loupe will probably produce equal results due to the all the slop in the system. For infinity shots...again, probably not much benefit as the mix of DOF and Depth of Focus at the film plane, for infinity, is so great, its just plain overkill....


The bumble bee fiber optic reference you made.... this was simply an advertising piece on the Schott Web Site, it had nothing to do with what I was describing to you. I mentioned a Fiber Optic FLAT plate (which was also on the page I referenced) ...which you can replace your ground glass with for the type of continuous ultra fine focusing you crave.


I think I mentioned the quotes I had in the past on this for 4x5 ground glass, $5k+, probably more today. An alternative, which I mentioned previously is a Fiber Optic round plate, which fits under your loupe, this allows you to focus any aerial image at high rez at a given fixed plane..... eliminating the need for the wire over drilled holes technique.... you can often buy these plates at surplus houses for $15. Since they are surplus, you have to shop till you find the right size.... common sizes are the same dimensions of dime, some as large as quarter $.25. Try to find one with 3 - 4 micron fibers. I use them quite often in other optical projects, nothing can duplicate their capability.


Hopefully now, you can "move" with a more peaceful state of mind! Best of luck...

rvhalejr
8-Feb-2009, 15:04
Hopefully now, you can "move" with a more peaceful state of mind! Best of luck...

Thanks for the kind words. From this point forward "I surrender ..... white flag raised....." is in effect for me.

There are some back posts in the thread that may need to be made (likely to be mind-blowing and controversial at least to me for reasons given there) any responses should be with a quote so the posts appear back there in the thread and (before this point) and not subsequent to this one.,. Thanks before hand.,.

I would like posts from here forward to be "white flag posts" (to preserve my piece of mind). Also, from here forward I'm going to try and restrict posts to collaborative, high priority and non-controversial issues.

Bob, I can't find any dime sized optical fiber disks so if you run across one please email me (for my address and I will reimburse you).

If I understand you (and the disks) correctly, if integrated into a simple 90 degree pocket microscope stand it will negate the use of 75 degree and 65 degree microscope stand changes (for side and corner) and radial alignment allowing ONE loupe to do all the work. This would be a huge improvement (which may be one of the reasons for this New Products forum).

The "White Flag" uses of this envisioned uber loupe (35-45x, FOV <= .30" and custom plenum or hybrid view screen with different areas clear or frosted or even holes) being a better preview of AA Aerial Focus, DOF and Diffusion for newb tilt tinkerers (me) with eye sight that continues to deteriorate (lets me attempt to keep up with my pro photo mentors who seem to get fantastic results with just a 4-6x).

Thanks Again,

R.

bglick
8-Feb-2009, 17:16
Check Surplus shed, they have coin size fiber optic plates all the time.... usually $10 - $20 each.... if they were not surplus, they would be 10x this.... the key is, find one that is very thin, maybe 1mm thickness, and 2.5 - 4 micron fiber size is ideal. When you find the right diameter plate that fits a given loupe, buy-out all the inventory and mate them with the loupe... it will make a nice magnifier for aerial focus for photographing flat objects.....

With this set up, you will easily view on axis rays through the plate...however, when you move from the center outward, specially on WA lenses, you still have the "angled ray" issue... the fibers in the plate are in one orientation, hence they perform optimum on axis (straight rays). When moving off axis, it will still work, but a lot of light loss will occur and some resolution loss.... you would have to experiment with different WA fl lenses to see what is acceptable. For Normal and Long lenses, you can go to the edges with no problem. And yes, it would eliminate the need to tilt the magnifier, as now you will be viewing a flat plane (the fiber optic plate) which the magnifier is designed for.

rvhalejr
8-Mar-2009, 15:18
...micro holes with a small hand pump will make the film perfectly flat...

Just a little update in the pre-white flag portion on the thread.,.

I've had film perfectly flat by using roll and tape method. It would be very cumbersome
to do this in a film bag (with an IR Camera) or in a dark room (with an IR head set) and with a custom designed holder. But what I really do not like about it is that after 24 hours the tape begins to stretch and film visibly buckles.

I've got a bunch of .020" bits and will try to test it out during break time (in between getting ready to move). The micro holes are my last hope at trying to find a practical method getting nearly the same OFR for 4x5 sheet as 120/220 roll.

rvhalejr
17-Mar-2009, 11:53
Just a little update in the pre-white flag portion on the thread.,.

I've got a bunch of .020" bits and will try to test it out during break time.,.

Tried the bits (.011 - .026") with various hole patterns and vacuum strengths but they failed the specular reflection test. Admittedly I need to quantify the film specular reflection with a small lp/mm target (at 90 degrees) to that of a mirror (the control).

A sample optical fiber disk was tested (could not get one to Bill's spec) and it does negate the need for tilting the loupe when off axis. The problem with the test disks I got (cheap $3 ones) was that the the resolution is low (maybe good to about 10x).

My next attempt will probably be to fabricate a roll-tape holder and measure real OFR from a prototype and decide if further experimentation is warranted. My latest wild idea is that maybe a small laminating like device (with opposed rollers) might used to produce a lot of perfectly (specular reflection) flat sheet film mounted on septums that could be loaded into prototyped film holders for exposure.

Oh well, back to my moving chores.,.

Helen Bach
19-Mar-2009, 04:15
Why not simply take a normal loupe and grind the shield (or attached side-plates) down so that when it is rocked on the rear surface of the glass (to align with the exit pupil) the focus remains on the front of the glass (or where the front of the glass would be if using an aerial image with cross-hairs or whatever)?

Apologies if this has been mentioned before, I expect it has but I didn't see it.

DIY vacuum film holder:
http://www.deadbread.com/crumbs/vac.html

Best,
Helen

rvhalejr
16-Apr-2009, 14:02
Why not simply take a normal loupe and grind the shield (or attached side-plates) down so that when it is rocked on the rear surface of the glass (to align with the exit pupil) the focus remains on the front of the glass (or where the front of the glass would be if using an aerial image with cross-hairs or whatever)?


I'm getting ready to move (still) so I've got to keep it short. What you describe above should work. However, I'm interested in the limits of fundamental elements (focusing, CIE color space - nice to see some on your site, diffusion, etc.) for the principle analog references (BW, E6, C41).

I've been able (arguably) to cross-correlate comparisons of the final end product in pixels regardless of the source (analog or digital) reasonably well. In order to do that
I've tried to introduce a lot of precision (that many here find boring) and identify weak
links. What works best for me is the 30x to 35x loupe while most here seem to prefer a 6x.

IMHO its difficult to get repeatable ultra fine focus behind a fresnel and ground glass, that led to the plenum (as a stand off for the emulsion plane) and so on. Admittedly getting the maximum number of pixels out of a piece of film is often not as important as other factors (which film/filters and lenses, color space, dynamic range, acuity, etc.).

Anyway, the tool set seems to be useful in pinpoint evaluation of an entire frame when using tilts and shifts or evaluating an ariel perspective.

R.

rvhalejr
20-Apr-2009, 12:19
http://www.deadbread.com/crumbs/vac.html


Nice mirror like reflection off the film (at that URL), but (sadly) it is an example of a non-flat surface.

While packing up I found the "Linhof Super Screen" holder for the GG (and fresnel) I use on the 4x5 Speed Graphic.

Back to sorting and packing, (sigh).,.

R.

Nathan Potter
20-Apr-2009, 16:13
rvhalejr, will you ever be done moving!

As I believe I mentioned a while ago I machined a vacuum holder for use with old Kodalith graphic arts film for early microelectronics lithography reproduction. I used an optical flat with sodium monochromatic light to assess the flatness of film clamped by vacuum. But the reflection off the first surface of the film can give a decent sense (though not quantitative of course) as shown in Helens' reference.

But the holder I used was machined from type 302 stainless IIRC. There were holes of about 0.032 diameter spread uniformly from edge to edge on maybe 1/4 inch centers for a 4 X 5 format. The back of the plate was hogged out everywhere yielding full vacuum access to all nominally 500 holes. The trick was to fabricate the entire plate then anneal the stainless followed by slight surface grinding to obtain optimum flatness. I have to guess now but I believe the TRO (Total Run Out) over 4 X 5 inches was less than 5 um - say 10 sodium fringes. However errors in film surface flatness depended critically on particles trapped on the platen surface and that often caused TRO to approach 100 um. We finally resorted to a laminar flow clean setup.

Helens notion of a swival loupe, especially for the high mag you want, I may have mentioned earlier. But it will produce only a one dimensional line of sharp focus either on GG or of an aerial image as observed by the viewer. :) :)

Nate Potter, Austin TX.

rvhalejr
21-Apr-2009, 13:03
rvhalejr, will you ever be done moving!


Good Lord willing. Our church is helping us move, but yesterday we almost hit 100 degrees so its still a pretty scary proposition.

Thanks for posting your specifications (w.r.t. the vacuum back) which are much better than mine (I gave up at a hole density of about 200).

I'm going to come clean on the fine focusing yield and scanning thing. Arguably my best scan results are achieved when the film is held perfectly flat (I don't use a drum scanner) but newton's rings usually ruin it.

I found some mounting fluid, plastic and/or glass with nearly the same refractive index as film emulsion (gelatin) and the acetate base. Matching the r.i. on either side of the film would hopefully attenuated newton's rings to extinction.

Anyone with common sense would have probably found it cheaper and easier to get an old tango.

R.

rvhalejr
22-Jun-2009, 13:53
rvhalejr, will you ever be done moving!

Whew !!! We are finally in the new place (Cheers !!!). The bad news is that some where in 100 or so storage boxes is the Large Format equipment. It will be a number of months before a small studio/lab is set up and R&D started again.

R.

rvhalejr
11-Dec-2009, 18:26
.,. The bad news is that some where in 100 or so storage boxes is the Large Format equipment. It will be a number of months before a small studio/lab is set up and R&D started again .,.

R.

Still trying to unpack boxes.,. To make matters worse I feel the need to fab a universal holder that will slip on as many lenses as possible and hold the Cokin P holder in place.

The threaded ring adapters and goose-neck clamp are rather awkward .,.

R.