PDA

View Full Version : A question about large format optics



claudiocambon
8-Feb-2007, 02:17
In a discussion with a friend recently, I maintained that there were optical qualities unique to large format that medium format digital could not reproduce, regardless of the power of resolution. I claimed that only large format lenses can reproduce things like the many gradations of focus, and that a small or medium format camera would always retain a certain optical affect that related to the physical size of the lenses and film area.

My friend disagreed, saying that it has to do with the power of resolution. Small and medium format film cameras do not show a comparable gradation of focus because the film size is small in relation to the film grain, and that limited resolution power eliminates the optical clarity which large format film instead has. He claimed that, once full clarity is achieved with medium format digitally, that you would see that same optical subtlety as in large format, because that ratio of resolution power to film area would have been greatly increased to transcend the limits previously imposed by film. So he says it is not unique to large format, but is a question of resolution.

I'm awl cornfused! Who is right?!

Walter Calahan
8-Feb-2007, 05:23
Does it really matter who is right? As long as the tools we use match our photographic vision, then the resulting image will express our artistry. All the rest is simply engineering.

Leonard Evens
8-Feb-2007, 06:27
In a discussion with a friend recently, I maintained that there were optical qualities unique to large format that medium format digital could not reproduce, regardless of the power of resolution. I claimed that only large format lenses can reproduce things like the many gradations of focus, and that a small or medium format camera would always retain a certain optical affect that related to the physical size of the lenses and film area.

I don't know what you mean by "gradations of focus". The optics of medium and large format lenses are basically the same. But any view camera, medium or large format, will allow placing the plane of exact focus, within limits, where you want it by tilting and/or swinging the standards. For the same scene with the same angle of view and point of view and same size final print, medium format actually provideds more depth of field at the same relative aperture, but diffraction will kick in sooner.



My friend disagreed, saying that it has to do with the power of resolution. Small and medium format film cameras do not show a comparable gradation of focus because the film size is small in relation to the film grain, and that limited resolution power eliminates the optical clarity which large format film instead has. He claimed that, once full clarity is achieved with medium format digitally, that you would see that same optical subtlety as in large format, because that ratio of resolution power to film area would have been greatly increased to transcend the limits previously imposed by film. So he says it is not unique to large format, but is a question of resolution.

I'm awl cornfused! Who is right?!

Generally, medium format lenses are capable of somewhat higher resolution than large format lenses because the latter are usually designed for movements and have larger coverage than the format. Even so, many large format lenses compare favorably to typical meidum format lenses, so this may not be a significant factor. In any case, the obtainable resolution will be a combination of the resolution of the film and that of the lens. Since medium format has to be enlarged more for the same size final print, you are more likely to challenge the resolution limits imposed by the combination. I'm not sure what you mean by achieving full clarity digitally. Right now, digital backs for either medium or large format can't compare with film, although that may be possible in the not too distant future. If you were able to eliminate the resolution of medium, film or digital, as a singnificant factor---by making it much larger than that of the lens---then the resolution of the lens would be the limiting factor. Ideally, as noted above, a lens designed for medium format might be enough better than a comparable lens designed for large format, that, after accounting for the degree of enlargement necessary for the final print, you wouldn't be able to tell the difference. But I believe we are now pretty far from that situation. So, for the moment, if you are interested in resolving fine detail, you are more likely to be able to do it with large format than with medium format, at least for large prints which will be viewed close up.

Jim Galli
8-Feb-2007, 07:29
You are right. Like most, he is only thinking in terms of ultimate sharp resolution. Even the jump from 4X5 to 8X10 makes an enormous difference in the out of focus rendition of a fast lens that covers the format. There is no way to duplicate how an f4 lens sees the world on an 8X10 camera. If the only thing in question is ultimate sharp resolution which is all the digital world has to offer, he'd be close. He's got about 3,000 X 4,000 chances for smooth rendition. Grain in 8X10 has billions.

photographs42
8-Feb-2007, 08:54
I suppose there is nothing wrong with a friendly debate over such things but the reality is there is no clear answer. Personally, I don’t even understand the question because I don’t understand what is meant by terms like “power of resolution”, “gradations of focus” and “once full clarity is achieved”.

I happen to know a number of people who are consumed by the unending argument of “this piece of equipment is better than that piece of equipment.” They buy and sell and debate and argue and brag about their superior lens or camera or whatever and take considerable pride in owning “The Best”. They can recite nauseous amounts of data proving they are not wrong.

Most of these people have never made a meaningful photograph in their life. Most of these people don’t even care about making photographs.

If your interest is in making photographs, choose the tool that works for you and don’t worry about what the other guy is using. If I have a piece of equipment that is not performing to my standards, I replace it with something that will. I happen to use a 5x7 Linhof Technika and I have lots of lenses of various makes and focal lengths. My tools work for me. They might not work for people doing other types of photography but that is irrelevant.

Jerome

claudiocambon
8-Feb-2007, 09:32
I should specify, I am not interested in what is sharper as an abstract argument. I am interested to know whether there is a difference in optical affect between lenses of different formats.

Let me be more precise about my example. I love the way I get focus fall off on a large format neg when I do a portrait up close: I hold the tip of the nose to the eye, and by the ear there is this beautiful transition as the focus falls off. What I would like to know is, is that optical affect a physical function of the large format lens, unique to that format, or merely the result of large format film's resolution power; if a medium format digital back had that power of resolution, would I get that same gradation of focus or not? That is why I am interested in understanding what the difference might be, if any, between the different formats.

Christopher Perez
8-Feb-2007, 09:35
If it really matters, I would ask your friend for Verifiable Objective Evidence to back up his/her statements. Not just theory or thoughts.

The physics of optics does NOT change just because you go from medium format to large.

I have looked a related questions (if I understand the nature of your question, that is) "six ways to Sunday" and have to agree with St. Ansel. Late in his life he said "...Knowing what I know now, any photographer worth his salt could make some beautiful things with pinhole cameras..."

Which is, to me, a way of reminding us that cameras and lenses (or pinholes) are just tools to an end, not the end in themselves.

Jim Jones
8-Feb-2007, 10:11
I consider the size and characteristics of the film to be more important than any magical or mythical difference in 35mm, MF, or LF lenses. Human vision is remarkably complex and sophisticated. We can subconsciously recognize differences between prints which, according to some technicians, should be essentially identical. This is where the size of the film (or more precisely, the degree of enlagement) becomes important.

C. D. Keth
8-Feb-2007, 10:31
No, the optics don't really change. You could easily build a mount to put a LF lens on a 35mm slr, a hasselblad, or a DSLR. The results from all of those experiments would be roughly the same as any other len on the given format. The only real difference between LF lenses and others is that LF lenses don't focus, the cameras do.

walter23
8-Feb-2007, 10:48
I think there are differences in the transitions from in-focus to out-of-focus areas between formats (and similarily, the amount of your depth of field). This is just a function of the focal lengths (larger format = longer focal length for a given field of view) and circles of confusion (probably larger for larger formats because of smaller enlargemen factors). You can certainly get shallower depth of field with a larger format, and I think more gradual transitions from in focus to out of focus (ie, a moderate wide angle with focus gradually drifting off into the distance is harder with a smaller format and impossible with something like a pocket digital camera with a teeny sensor and relatedly small focal lengths).

walter23
8-Feb-2007, 11:08
What I would like to know is, is that optical affect a physical function of the large format lens, unique to that format, or merely the result of large format film's resolution power; if a medium format digital back had that power of resolution, would I get that same gradation of focus or not? That is why I am interested in understanding what the difference might be, if any, between the different formats.

I think there is a physical difference that has nothing to do with resolution, and more to do with depth of field and the optics of what is considered to be "in focus". This is a mix of intuition (which in physics can be pretty wrong, I know) and empirical observations, and facts about depth of field. A 6x6 negative with an 80mm lens at f/5.6 will have more depth of field than a 4x5 and a 180mm lens (or whatever the 80mm equiv would be) at f/5.6. That's why if you use a 35mm SLR you can achieve much more beautiful focus fall off effects than with a tiny compact digital point and shoot which has virtually infinite DOF at any moderate focal length wherein a normal lens is something like 10mm. There's a counteracting effect of enlargement (ie, with a 2/3" sensor or whatever on a tiny digital you're enlarging many fold and therefore focus differences will become more apparent) but the lens focal length differences (for a given point of view) are stronger and you see lower DOF at larger formats.

I'm not sure how this relates to the gradual nature of focus fall off, but empirically it seems like larger formats can give more gradual transitions from in focus to out of focus. If you could quantify focus (some function of the circle of confusion and spread of light or whatever) it would be cool to calculate "focus curves" showing how focus falls off in different formats as a function of distance (and lens, aperture, and focusing distance). Anybody want a programming project? ;) I might try this out for the sake of curiosity sometime if I can find the right formulae.

C. D. Keth
8-Feb-2007, 12:01
I think you would find that physically, the focus is doing the exact same thing for a given enlargement ratio, f/stop and subject distance. The difference in larger formats, I think, is that the ability to record smaller increments of out-of-focus is present. With smaller formats (I see this daily working with video, which has comparably tiny sensors and terrible resolution to even consumer digicams) the focus all of a sudden seems to snap soft rather than transition. When I shoot 16mm it's a bit better, when I shoot 35mm it's better still.

I think it's a resolution issue, but I have not performed controlled experiments to prove it.

Edit: Something else just occured to me. LF lenses are often not of the same optical quality that top-shelf lenses for 35mm, or for cinema use are. The enlargment ratios for LF simply don't need it and they would become prohibitively expensive like cinema lenses (20-30k per prime is the going rate for the newest set of Arri/Zeiss lenses). This might make the transition a bit smoother since the in-focus areas aren't technically as in-focus as a brand new set of zeiss master primes would make it, for example. The trick is that it doesn't matter since LF will be enlarged a few times and the 35mm MP negs will be enlarged to the size of a large wall. Just a thought.

walter23
8-Feb-2007, 12:42
I think you would find that physically, the focus is doing the exact same thing for a given enlargement ratio, f/stop and subject distance.



I don't think so.

4x5 film (162mm diagonal), 180mm lens, f/5.6, 10 foot focusing distance:
Subject distance 10 ft

Depth of field
Near limit 9.52 ft
Far limit 10.5 ft
Total 1 ft

In front of subject 0.48 ft (47%)
Behind subject 0.53 ft (53%)

Hyperfocal distance 188.5 ft
Circle of confusion 0.1 mm

6x7 film (92.1mm diagonal), 100mm lens (using diagonal for equivalences), f/5.6, 10 foot focus:
Subject distance 10 ft

Depth of field
Near limit 9.3 ft
Far limit 10.8 ft
Total 1.51 ft

In front of subject 0.7 ft (46%)
Behind subject 0.81 ft (54%)

Hyperfocal distance 129.2 ft
Circle of confusion 0.045 mm

35mm (43mm diagonal), 47mm lens, f/5.6, 10 foot focus:
Subject distance 10 ft

Depth of field
Near limit 8.13 ft
Far limit 13 ft
Total 4.87 ft

In front of subject 1.87 ft (38%)
Behind subject 3 ft (62%)

Hyperfocal distance 42.9 ft
Circle of confusion 0.03 mm


I don't know exactly what goes into those DOF formulas, but I think it's based on a standard enlargement size.

This is from http://www.dofmaster.com/dofjs.html (the standard online DOF calculator tool). You can see clearly that DOF increases as format size decreases and it's not just about resolution; the decreasing focal length (for an equivalent field of view) dominates the calculation, so in 4x5 you'd have 1 foot DOF, 6x7 about 1.5 feet, and 35mm about 5 feet.

Gordon Moat
8-Feb-2007, 12:57
There are a few other ways to look at this. It is now possible, through a few companies, to place a D-SLR, or medium format digital back, onto a large format (4x5) camera. Using either a sliding adapter, or movements of the back standard on the view camera, you can use the exact same large format lens for 4x5 film, stitching a few digital back shots, or stitching many D-SLR shots. The resulting images should be very close in terms of DoF or focus fall off.

Consider that, for example, a 135mm lens on a 4x5 would still be a 135mm lens on medium format, and still an 135mm lens on 35mm (or full frame D-SLR). Without changing camera to subject distance, the DoF would actually be nearly the same on each. The main difference would be that without stitching the smaller format shots together, your FoV (field of view) would be more cropped on smaller formats. You could shoot 4x5, and cut out a 24mm by 36mm or 56mm by 72mm part of the film, though in practice hardly anyone does this.

To get a headshot (top of head to shirt collar) on 4x5 with a 135mm lens, your focus distance is 0.5m away. At f5.6 the DoF is 0.011m. A 6x7 medium format shot with the same lens (and f5.6) would only show the nose to top of head, and factoring different CoC would indicate 0.006m DoF. A 35mm (or full frame D-SLR) shot at 0.5m distance (and f5.6) would be another CoC calculation indicating 0.003m DoF, and only show a little more than one eye of the subject. However, if you wanted to get the same headshot on each format, with the 6x7 you would probably use an 80mm lens at the same distance, and perhaps a 50mm or slightly wider FoV) on 35mm (or full frame D-SLR). With the 50mm, even with different CoC, the DoF would be about 0.026m at f5.6 and 0.5m, while the 80mm on 6x7 would be about 0.020m DoF.

Playing around some more with the calculations and variations in pCAM software on my Palm, an 80mm lens on 6x7 at 0.5m distance for a headshot could be done at f2.8. In such a setting, the DoF drops to 0.010m. Using a 50mm on a 35mm camera, you could have an f1.4 aperture setting, giving a DoF of 0.006m. So that effect of focus falloff could be achieved in a few different ways. Notice I did not pick exact comparible focal lengths, but I did choose more commonly available lens choices (a 40mm f1.4 on 35mm would be another possibility)

Ciao!

Gordon Moat
A G Studio (http://www.allgstudio.com)

Mark Sawyer
8-Feb-2007, 14:59
I suspect that as far as the "feel" of the lens goes, large format photographers have a much, much wider choice, and it reflects in a *lot* of the work seen here. How many vintage/classic optics or soft-focus options does the medium-format user really have to choose from?

I think the soft-focus effect is undergoing a renaissance similar to the upsurge in interest in large format, and while there are only a few modern soft focus lenses available, there are quite a few older ones still working wonderfully well. It's worth remembering that once upon a time, such lenses were an very important part of a lens-makers catalog. In 1919, Wollensak had five separate lines of soft/diffused focus lenses (Vitax, Verito, Voltas, Vesta, and Versar), but only one "sharp" general purpose line of lenses, the Velostigmat. And even at that, many Velostigmats were produced with a diffused-focus adjustment built in...

Paul Fitzgerald
8-Feb-2007, 20:25
"Let me be more precise about my example. I love the way I get focus fall off on a large format neg when I do a portrait up close: I hold the tip of the nose to the eye, and by the ear there is this beautiful transition as the focus falls off. What I would like to know is, is that optical affect a physical function of the large format lens, unique to that format, or merely the result of large format film's resolution power; if a medium format digital back had that power of resolution, would I get that same gradation of focus or not? That is why I am interested in understanding what the difference might be, if any, between the different formats."

If you took a standard portrait lens and set-up a portrait shot and changed nothing else but the film back size (5x7, 8x10, 11x14) they would each 'look' different. I guess it's a subconscious perception or a trick of the light, but it's real. It could just be the comparative 'real-estate' of the films allowing more of the 'character' of the lens to be seen at the same time.

just a thought.

Leonard Evens
9-Feb-2007, 06:01
I should specify, I am not interested in what is sharper as an abstract argument. I am interested to know whether there is a difference in optical affect between lenses of different formats.

Let me be more precise about my example. I love the way I get focus fall off on a large format neg when I do a portrait up close: I hold the tip of the nose to the eye, and by the ear there is this beautiful transition as the focus falls off. What I would like to know is, is that optical affect a physical function of the large format lens, unique to that format, or merely the result of large format film's resolution power; if a medium format digital back had that power of resolution, would I get that same gradation of focus or not? That is why I am interested in understanding what the difference might be, if any, between the different formats.

Partly this would simply be a matter of depth of field. You can certainly obtain the same DOF for a given scene and given angle of view with medium format that you do with large format, but you would have to use a larger aperture. If you concentrate on the final print, I believe the circles of confusion would behave the same way for comparable setups, where the focal lengths and apertures are appropriately adjusted.

But what you describe seems to relate to the way the image goes out of focus as you pass through the limits of DOF. I don't know for sure, but I believe this may relate to bokeh. Try en.wikipedia.org/wiki/Bokeh or do a google search. Bokeh describes how the shape of the diaphragm, lens aberrations, and other things may affect the appearence of out of focus regions. It is generally a function of the specific lens. Off hand, I see no theoretical reason why it should depend on the format, but since there are so many factors to consider and since much about bokeh is subjective, it is possible that format size is one factor affecting it. It is also possible there is some systematic bias in the design of large format lenses which might affect it, but in principle, at lteast, you ought to be able to obtain essentially the same effect with two lenses, one for large and the other for medium format.

Struan Gray
9-Feb-2007, 06:28
If you double the size of the negative you have to double the focal length to get the same field of view and stop down two stops to get the same depth of field. In principle this can be done.

However, going up in format you either need to get hold of a faster film (which will, in general, look different) or accept longer shutter speeds (which will, in general, look different).

Going down in format you need to find a faster lens, which may not be possible, or which may be dominated by aberrations at the aperture you need to use (which will, in general, look different). Failing that, you may find diffraction blur is an issue (which will, in general, look different).

LF is a regime where it is easy to have a short depth of field on large objects while the out-of-focus parts look pleasingly symmetrical and even. Tonality is super-smooth.

Small formats like 35 mm and below are a regime where it is easy to get everything in focus. Tonality is gritty and grainy.

Leon Jester
12-Feb-2007, 16:30
If you double the size of the negative you have to double the focal length to get the same field of view and stop down two stops to get the same depth of field. In principle this can be done.

However, going up in format you either need to get hold of a faster film (which will, in general, look different) or accept longer shutter speeds (which will, in general, look different).

Going down in format you need to find a faster lens, which may not be possible, or which may be dominated by aberrations at the aperture you need to use (which will, in general, look different). Failing that, you may find diffraction blur is an issue (which will, in general, look different).

LF is a regime where it is easy to have a short depth of field on large objects while the out-of-focus parts look pleasingly symmetrical and even. Tonality is super-smooth.

Small formats like 35 mm and below are a regime where it is easy to get everything in focus. Tonality is gritty and grainy.

If you use the long + short formula for a portrait lense you won't get the same depth of field, regardless.

To wit: 35mm with this formula would use a 60mm lense, 6x6 would use a 120mm lense, 4x5 would use a 9 inch (228mm) lense, 5x7 would use a 12 inch (304.8mm) lense.

As far as film resolution goes, the faster the film the grainer it is, simply because of the physical makeup of the emulsion. A portrait shot on, say, Panatomic X is going to have a vastly different appearance and tonal value than one shot on Super XX or Tri-X.

Use whatever works for you, that's going to be part of your photographic style.

jb7
13-Feb-2007, 17:16
In my opinion, there is no mystery-
the combination of image size,
coupled with choice of aperture,
will have the same optical effect-

For an original image, (disregarding magnification of that image for a moment)
depth of field will be the same for any 300mm lens,
for example,
whether shot on a digital or a 10x8.

The difference is,
not many people will consider a 24x36mm image to be the finished product.
whereas, with 8x10, it might be.

Apart from an unsuccessful bid to flog a lens,
this is my first post-
I must admit to being a little intimidated by the absolute erudition of the contributors to this site, and I find it to be an invaluable resource.

Now that I've popped my posting cherry,
maybe the next one wont be so difficult-

joseph

Emmanuel BIGLER
14-Feb-2007, 04:45
I must admit to being a little intimidated by the absolute erudition..

Erudition ? Nooooo!

If I may add my 0,02 euro to this discussion.

If the wavelength of light was infinitely small and if pure geometrical optics + classical lens aberrations were the ultimate model, and using a perfect detector with no noise and no resolution limit, I do not see any reason why a certain format would be better than another. Even classical DOF models would have to be re-visited wince DOF is not intrinsic to a given focal length or format, it is directly related also to a certain sharpness criterion. So beware, if you intend to do contact-prints-only with you Rolleiflex 6x6 TLR (like in most B&W family albums up to the sixties), the actual DOF might be much larger than what has been engraved on the focusing knob of your Rollei-TLR since... at least WW-II or even 1929 ;)


But in practice we have of course several limitations. In the age of film-only photography we had to live with the intrinsic limitations of silver halide layers. Well, in the past and still today, there has been gum-bichromate, cyanotypes, palladium-platinum, xerox copy, vidicon tubes and Zworykin's Iconoscope, and many other analog means of recording an image, but let's consider silver halide first since it has undergone the most of research an development for high quality still photography.

The advantage of film is that the performances of a given film in terms of sensitivity and grain/noise is basically unchanged when you coat one square metre of film for use in a mammoth still camera or when you use the few millimetre square of a super-8 movie camera frame. So definitely there is an advantage to use a big size of film with lesser final enlargement: getting rid of film grain and getting better gradations in gray levels because you have bigger film-pixels with little grain noise when scaling up the size of the medium. And since LF lenses are not zooms, designed for demanding professional users, and are always (or should be ;) ) used at their best f-stop where diffraction balances residual aberrations, you get in LF the best optical quality that can be recorded in one pass. There is an on-going discussion about stitching, suffice to say that for copying flat objects, a scanner appears much better than a repro bench because the scanner lens does not have to transfer all the
image elements in one step, so the lens can be optimised for a smaller field and a better resolution, thanks to the stitching done in the scanner. So the good side of the demise of copying benches is the nice apo-ronars that we can get for affordable prices ;)

But we canot forget that the wavelength of light is not infinitely small. Well 0.5 micron is not at our scale, so what's the matter ? In fact if you look at the best f-stop for 35mm, medium and large format cameras, you find that, very roughly, the optimum f-stop for standard lenses, those which cover about 50 to 70°, follows the empirical rule

f-best = (focal length in millimetres) / (8 millimetres).

For example the best f-stop for a 150mm covering 4x5 is about 16-22. the best f-stop for a 300 covering 8x10" would be closer to 32. The best f-stop for the 100mm Carl Zeis Hasselblad Planar is f-8. And the best f-stop for a 50mm standard lens for the 24x36 frame is about 5.6

Last generations of LF standard lenses like the apo-sironar or its competitor in Bad-Kreuznach probably exceed this figure, f/11-f/16 being the best f-stop and not f-16/f-22.

An amusing consequence of this scaling law is that if you relax the sharpness criterion proportionally to the format ( the CoC set to F/1720 or so) and if you always use the best f-stop for you lens, DOF is the same for all formats !! the only difference is that you'll need many more photons to get your LF image, and this is the price to pay for bigger film-pixels with a superb half-tones gradation and low grain noise.

If we extrapolate this rule to smaller formats, we can be frightened since the best f-stop for a standard lens covering the so-called 1/2" format, diagonal = 8 mm should be f/1 or so !!

Even if lens design and glass manufacture has made tremendous improvements, I do not believe in a f/1 lens covering 8mm in diagonal that would outperform, on the final print, the good ol' 75 mm tessar @f/11 on my Rollei TLR ;)

The reason for this scaling rule is the balance between residual aberrations and diffraction. Residual aberratiosn scale like the format but diffraction does not. So all formats are not born equal, the larger, the better. Because of diffraction.

So to me there will always be ultimate advantage for larger formats, the fact that diffraction becomes negligible. Now which is the smallest format that is worth using? The border is really fuzzy and depends on how much you demand in terms of image quality and how good you detector is. And how much you ask for camera portabilty and compactness..

If you look back to the history of photography, the same story was told to both the professionals and the consumers : due to progress in film, you do not need this big camera. Stop using your Graflex, take a Rollei. Stop using your Rollei, take a Nikon. The story stopped some time in the '90s when even families realized how bad the quality of the 110 format was... and 35mm ruled. By charity, I'll not remember the story of the APS format. So why ultra-small digital formats are now considered as acceptable ?

The man advantage of digital sensors, now that we have a sufficient number of pixels is that the detection efficiency of silicon sensors far exceeds what best films can do. For example only the best films used for astrophotography could reach a few percents in terms of equivalent quantum efficiency, while current silicon photographic image detectors can reach about 20%. In other terms, you can use much smaller silicon pixels for the same final noise. Sure there are some issues like micro-lenses to collect photons, but anyway, silicon is intrinsically much better at catching photons that silver halide crystals are. We could remember that at the end of the XX-st century, a French team of scientists leaded by Mme Jacqueline Belloni patented a method to dramatically improve the efficiency of film.

http://www.cnrs.fr/cw/en/pres/compress/emulsionsphoto.html

The partner film company the the time was named... Agfa. No comment.

Film has a very low efficiency, so since Nicéphore Niépce Himself we have been waisting more than 99% of good photons. Improvements since the fist bitumen process (8 hours of exposure in bright sunshine) have been tremendous, and in the last 20 years of the XX-st century, we can say that 25-ISO film has been replaced by 100-iso films with better grain performance ! So probably a factor of 4 in efficiency or so. But still film cannot exceed a few percent in quantum detection efficiency.

Whereas a single silicon photodetector used in instrumentation can exceed 80% in terms of quantum efficiency. We are still far from this figure for tiny pixels in an image detector but there is hope for continued improvement. Whereas it is unlikely that developments following the discoveries made by Mme Belloni's team will ever been transferred to a real-world product...

So to me we have been lurred by considering lateral resolution and equivalent pixel count issues only. Sure, holographic films are capable of recording 5000 line pairs per millimetre and this is enjoyable for recording holograms, but what about detection efficiency?

To me and probably most of us the situation is that digital images do not require as many pixels as you would expect from the resolution limits of lens +film because they show virtually no grain noise in areas like skyes where there is no texture.

Two years from now, discussing with a French professional photographer who had been digitizing his LF slides for months and could compare to what he was directly recording with a digital SLR, he suggested that we should at least use twice as much surface of film to get the same final image quality after digitizing. Probably the real figure is something like 4 times in terms of equivalent surface, 2 times in linear dimension. You could object that you do not want to digitize film and wish to stay 100% analog in your darkroom, so the comparison might not be really meaningful. OK but behind this I can see only one reason why silicon images appear so good, i.e. the question of noise.

So a possible conclusion is that we could get the same image quality with a silicon sensor 4 times smaller in surface, and this is no mystery, a 645 digital sensor probably exceeds in quality what you'd get with a 6x9 digitized film. But anyway once you've made this factor 4 in surface or this factor 2 in linear dimension of the detector, the advantage of larger formats still holds due to the best f-stop issue, due to diffraction that does not scale. I think nobody will object that a 645 digital camera outperforms a four-thirds...

So when "they" will sell a 6x9 silicon sensor for less that 1500 dollars, sure I'll stop using film. In the past I had set to myself a limit of 1 megapixels before even starting to consider digital images. This limit was reached by the industry in consumer products much faster that I had expected. Even the cheapest camphone has now more pixels ;-)

So why don't I stop using film and switch to digital? Because even if I am convinced of the superiority of silicon over silver halide as an image detecteor, I am not a professional producing images for magazines, books or newspapers and making a living on ot. So I do not care for longer exposure times, slower process, expensive films (I'm spending more money in gas and car expenses to go on location for leisure landscape photography than I spend in film and chemicals) and I want to control all the process myself. Starting on the ground glass with my eyes. Not through an electronic display through a software.

GPS
14-Feb-2007, 06:20
[i]...
So when "they" will sell a 6x9 silicon sensor for less that 1500 dollars, sure I'll stop using film. ...

Waiting for the same at this end too, but there is yet another issue that puts me off the digital - its storage. And that is harder to overcome than just the resolution and the price issues. Do you want to have 50 years of your work stored on a hard drive that itself will be useless in ... (read -much less than 50) years? Remember the recent story about the Apollo films from the Moon lost in Nasa? Some said that they were digitized so the originals were not so necessary to keep... Ha ha...

paulr
14-Feb-2007, 07:18
[i]Last generations of LF standard lenses like the apo-sironar or its competitor in Bad-Kreuznach probably exceed this figure, f/11-f/16 being the best f-stop and not f-16/f-22.

I think this depends a lot on where in the field of view your most important detail is. I find that the veering toward the wider apertures slightly improves sharpness on axis, and slightly diminishes it off axis.

This is most evident with my enlarging lens (a 150 apo componon hm), which is always dealing with a flat plane of focus and no significant variables. If it's mostly sky and dirt in the corners, I'll use it at f11 and get blazing sharpness in the middle where the detail is (and where the eye tends to go). But if there's important detail in the corners, I usually get more pleasing overall results at f16.

Interesting post, overall, by the way.

I wonder if the day will come when there's an affordable, drop-in 4x5 inch digital sensor, which would let old timers like us keep our gear and our familiar ground glasses.

Emmanuel BIGLER
14-Feb-2007, 09:22
I agree with Paul R that there is probably a trade-off between overall coverage and sharpness at the centre; we are dealing with lenses resulting for almost one century of optimisation so we are close to the limits of what a lens can transfer in one shot without stitching! I also agree that the cost of maintaining a digital archive of professional images is probably not taken into account in the film-vs-digital issue.

I also realize that my recent post is far too long and hard to read so I'd like to come back to the original question by Claudio Cambon, and summarise some ideas offered here to the group for contradiction/discussion

- LF lenses were optimised for different purpose than 35mm and MF lenses. Since they do not have to suffer from the design constraints of a flipping mirror or be useable as a zoom or at wide apertures for photo-journalism, they can reach the physical limits at the centre more easily. But apart from that important technical point, as well as the fact that LF users demand large image circle for movements, I do not see any reason why there would be something special optically speaking with LF lenses vs. MF if film or sensor resolution is not taken into account.

- recent progress in "digital" view camera lenses show that you can still have a gain in performance with a more limited image circle. Actually if we consider the recent LF lenses in digital series in the range of 40 to 90mm, they are pretty similar to a top-class MF lens, or will even outperform them. The issue of "lateral color" is however a kind of a new design constraint imposed by the structure of "Bayer" type of color sensors that was not taken into account when designing conventional "film" MF lenses.

- now there are some practical issues about the capability of the photographer to properly set tilts + shifts with a "small" sensor, say a 645-sized. One could object that post-processing will allow you to digitally remove unwanted blur and converging lines / keystone effects, but I am not sure that in terms of "paid" working hours, post-processing is cheaper than properly setting a view camera in front of the subject. My feeling is that if you have a well-built precision view camera coupled to a high quality monitor for live video you could in principle do the same kind of visual adjustments with a small sensor that one can perform directly manually in LF with a big ground glass. So again I do not see in principle any difference between LF and MF if the final sharpness criterion on the final print is the same. This might be a delicat issue, though, but I am always very cautious about comparative DOF considerations between formats when no sharpness criterion is precisely set.

- I do not see any real issue about manufacturing tolerances for lenses or lens focus adjustement between the MF and the LF range of lenses. However I am still convinced that scaling down the MF or LF designs down to a 8mm sensor is not reasonable if one wants to keep the same level of image quality. Of course million of consumer-grade cameras have lenses designed for this sensor size, but nobody really wants to make a side-by-side test between such a camera and a even a modest print from a 4"x5" neg or slide. Rodenstock has already had to develop a special centering procedure for precisely adjusting the last generation of digital view camera lenses in the shutter mount. So I'm convinced that scaling down this to a 8mm focal length while keeping the final image quality is not practically achievable at a reasonable cost. Another reason to believe in the future of sensor size in the 5-10cm / 2"-4" range and not in millimeter size !

Rakesh Malik
14-Feb-2007, 10:54
If you took a standard portrait lens and set-up a portrait shot and changed nothing else but the film back size (5x7, 8x10, 11x14) they would each 'look' different. I guess it's a subconscious perception or a trick of the light, but it's real. It could just be the comparative 'real-estate' of the films allowing more of the 'character' of the lens to be seen at the same time.

just a thought.

Yes, this is what they refer to as "cropping" in photography.