A question about large format optics

[claudiocambon]

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]

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]

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]

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]

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]

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.

[walter23]

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.

[Leonard Evens]

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]

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]

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.