4x5 Ultra Fine Focusing and Calibration

[bglick]

> 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]

> 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]

> 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]

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]

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]

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]

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]

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]

...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]

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.,.