Re: 4x5 Ultra Fine Focusing and Calibration
Quote:
Originally Posted by
bglick
>
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.
Re: 4x5 Ultra Fine Focusing and Calibration
Quote:
Originally Posted by
rvhalejr
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
Re: 4x5 Ultra Fine Focusing and Calibration
Quote:
Originally Posted by
rvhalejr
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.,.
Re: 4x5 Ultra Fine Focusing and Calibration
> 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...
Re: 4x5 Ultra Fine Focusing and Calibration
Quote:
Originally Posted by
bglick
> ....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.
Quote:
Originally Posted by
bglick
... 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
Re: 4x5 Ultra Fine Focusing and Calibration
> 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?
Re: 4x5 Ultra Fine Focusing and Calibration
Quote:
Originally Posted by
rvhalejr
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
Quote:
"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
Quote:
"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.
Re: 4x5 Ultra Fine Focusing and Calibration
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?
Re: 4x5 Ultra Fine Focusing and Calibration
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.
Re: 4x5 Ultra Fine Focusing and Calibration
Quote:
Originally Posted by
Nathan Potter
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.
Quote:
Originally Posted by
Nathan Potter
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.
Quote:
Originally Posted by
Nathan Potter
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.
