Format creep and diffraction

[Don Miller]

I recently purchased a 5x7 primarily to shoot 6x17 and long-lens 4x5. Now my 4x5 gg looks tiny. So, as a typical LF user I ask myself the next logical question: "I wonder what 8x10 would look like?".

I started with LF to make big prints. Chromes to scan. I shoot primarily small to medium scale landscapes and scenics with typical tilt and rise movements.

My question: At what point does diffraction from stopping down eliminate the benefit of a larger format? Looking on the web at Chris Jordan's excellent 8x10 chrome work, I realize that much of what he shoots can be done with narrow dof near the optimal aperture of an 8x10 lens. Is their really any large print benefit for typical outdoor work with 8x10 or 5x7 over 4x5?

Don

[Jay DeFehr]

Donald, I think there are two ways to address your question. One way is to ask a question of you; do you think that enlargement degrades image quality? If you do, then the answer is simple; more enlargement means more degradation. I know your question included diffraction as one of the variables, but most experienced LF shooters know how to use camera movements to overcome those differences, so I don't consider diffraction an important factor. The other way to address your question is to say that results are subjective, and there are too many variables to state categorically that a larger negative will invariably produce a better print, and only you can decide if the benefits of a larger negative outweigh the added complexity and expense that a larger outfit represents.

[Don Miller]

Jay, I do believe that enlargement degrades image quality due to the reason that most viewers (including me) won't stand back from the image "at the proper viewing distance". This is especially true of color photography from nature, as we have probably evolved with a keen sense of what things should look like in that environment.

From a technical perspective a digital printing workflow does not suffer the potential deffraction problems as a large darkroom print might.

I've never met any LF landscape shooter who doesn't daily trade some defraction for adequate dof. Is there a secret society of camera movement specialist I should know about?

I'm not looking for a hard answer, but simply starting a discussion for people with pratical experience. I also hope the "math guys" contribute, but once the formulas start flying I usually just look for the conclusion.

Don

[Jay DeFehr]

I don't think it's a "secret" society, but they're out there.

" I cannot imagine anyone having depth of field problems with an 8x10. Unless the situation is very extreme, you should, by judicious use of the front tilt and/or front swing (easier to use than movements in the back and also using movements in the front affects the image on the ground glass less) you should be able to get everything in focus wide open--then you stop down just to make sure."

M.A. Smith

[Ben Calwell]

In light of the above quote, I had a problem the other day with getting everything sharp. I photographed a spider in its web that it had spun over a window. I set up my old 8x10 equipped with a 300mm lens. The camera was about 4 feet from the window. I wanted the wooden window frames and the spider and web outside to all be in focus (the web was about an inch off the window glass), but I couldn't do it. I wound up focusing on the spider and stopping down to hopefully get the window frame in focus. When I stopped down, I couldn't really tell on the ground glass if the window frames were in focus ( it was a dark room). Since both subject planes (the spider and the window) were parallel to the film plane, how could swinging, tilting or other gyration of the front have helped in this case? I haven't developed the film yet to see how objectionally out of focus the window is. I'm hoping the sharp spider will make the photo work.

[Ralph Barker]

This might be a question similar to, "What is the sound of one hand clapping if the hand is rough and needs lotion." (A question which may fit nicely with the secret tilt/swing society, secret handshake notion.) ;-)

Seriously, I think there are many answers to the question, but none of them universally correct. Having added 8x10 to my repertoire only recently (about a year ago), the wow factor is still fresh in my mind when looking at the 8x10 GG. It's just gorgeous compared to 4x5, just as 4x5 was when compared to the viewfinder of a 35mm or medium-format camera. But, I think you are correct, Don, in describing it as "format creep".

While there are distinct advantages of increasingly larger negatives (or, chromes), there are both technical and practical issues that balance against those advantages. On the technical side, for example, one might argue about the degree to which the increased DOF/diffraction problem of longer lenses is offset by reduced enlargement factors. Or, how the technical issues are offset by the "yummy" factor of the larger GG and negatives.

One of the practical issues to consider, I think, is the availability and cost of enlargers. Enlargers for 4x5 are pretty common, but 5x7 enlargers somewhat less so. Enlargers for 8x10, however, are scarce by comparison, and considerably more expensive. So, while I thought I'd be happy with contact prints of my 8x10 negs, it didn't take long for the desire to enlarge them to creep into my mind. (There's that "creep" word again.)

In the final analysis, it probably boils down to the nature of the work one wants to do, and what fits well with both the technical requirements and the associated working style. Sometimes, the desire to simply do/use something different from the norm creeps into the decision process, something that will give our work a "hook". So, you might want to skip 8x10, Don, and jump straight to a 16x20 or 20x24 camera. Be the first on your block to use that new Schneider 500mm fine art lens. ;-)

[Jay DeFehr]

Hi Ben. According to my calculations, using a 300mm lens, you should have been able to get 4"+ of dof @ f32 with a hyperfocal distance of 308.6mm. Near distance 3.96', far distance 4.04'. No gyrations necessary.

[Emmanuel BIGLER]

Don. as a rule of thumb you can stop down a 8"x10" lens 2 clicks without suffering
from diffraction if you compare to a similar lens with half the focal length designed for 4"x5".
The problem of 8"x10" seems to me more the longer exposure times you'll need to achieve
the ultra-sharp results you deserve. So moving clouds, moving trees and moving corn fields might probably be the real problem, not DOF.

[David Vickery]

"My question: At what point does diffraction from stopping down eliminate the benefit of a larger format?"

My Answer: Never!

If you don't believe me then take a close look at the huge prints that Christopher Burkett makes. They are amazing. Or any other large prints, contact or enlargements, from other Craftsmen/Craftswomen working with 8x10 or larger film.

The idea that you will not have enough depth of field or sharpness with the larger formats is a myth. You should be more concerned with making enlargements from the smaller film sizes.

[Brian Ellis]

Diffraction is primarily a problem with smaller formats, mainly 35mm. IMHO diffraction isn't a problem worth serious worry with 4x5 and larger formats. I think that lack of sharpness due to insufficient depth of field will almost always be far more noticable than the minimal loss of image quality resulting from use of say f64 rather than say f22 with 4x5 and larger formats. I use whatever aperture is needed to gain the desired depth of field (based on my depth of field table and the distance the front standard travels between focusing on the near and focusing on the far), if that happens to be f45 or f64, so be it.

[Leonard Evens]

I agree with Emanuel. In actuality you get essentially the same range of f-stops with any format, if you assume the same size final print, but the range is shifted towards smaller apertures as you move to a larger format from a smaller format. If you double the linear dimensions of the format, you lose two stops at the large aperture end in terms of the DOF you get and you gain two stops at the small aperture end with respect to diffraction because you don't need to enlarge as much. But the total number of useful stops remains the same. The problem, as Emanuel points out, is that you have to shoot a slower speeds.

[N Dhananjay]

As already pointed out above, with larger formats you are not trading extra diffraction for increased DOF. You are trading speed for extra DOF. Diffraction basically increases the size of the blur circle and is a function of f stop (for a particular wavelength). Now on a larger format, you do stop down more for the same DOF, and therefore you do have more diffraction/lower resolution on the neg. However, the neg is being enlarged correspondingly less - that is, the blur circle is being enlarged less. Therefore, the size of the blur circle on the final print remains the same. So, in practical terms, what this means is that with a larger format, you trade speed for DOF - that is, you use longer exposures. Hope this helps, DJ

[Matthew Runkel]

According to Stroebel, "[t]he diffraction-limited resolution can be approximated with the formula R = 1800 / f-number, where R is the resolution in lines/millimeter and 1800 is a constant." Combining this information with your expected enlargement and an assumption about viewing distance should let you estimate the best results you could theoretically achieve with a perfect lens, perfect film, perfect film flatness, perfect enlargement, etc.

Stroebel also says that "[t]he human eye generally is considered to have a resloution of 10 to 14 lines/mm at a viewing distance of 10 in." This may be a useful generalization, but I'm sure it collapses/ignores many interesting variables.

[Emmanuel BIGLER]

Another issue about very small apertures is the precision of the shape and actual area of an iris when closed down to f/64 and more.
On older lenses with no aperture clicks and no real upper limit, at f45 and above the travel of the lever between two full stops becomes smaller and smaller and sometimes the iris shape becomes irregular. So for this very practical reason as well, small apertures with f-numbers, say, bigger than 2 stops past the best aperture are not really recommended.
But to me large format means freedom. Even freedom to play with diffraction. 35mm and medium format lens manufacturers decide for us for the maximum allowable f-stop ; upgrading to large format with old lenses allows you to play with "forbidden ultra-small apertures" ;-);-)