Curiosity testing for diffraction limitation -- very general

[Ulophot]

I included "very general" in the title, because I am not worried about numbers here. I have two lenses, a Komura Commercial 210 f/6.3 and Nikkor-S 135 f.5.6, which stop down to 45 and 64, respectively. Since my principal interest is B&W portraiture and I shoot only HP5 and print only to 11x14, both of these lenses is more than adequate for this purpose. I already know this and am perfectly happy with both lenses.

I am posting this in case someone sees something I am leaving out in my considerations, below.

I do shoot other subjects, and recently was shooting some flower and leaf still life scenes in the garden fairly close up, requiring small apertures even after movements. It piqued my curiosity about the lenses' performance at these f/32-and-smaller apertures, where I am aware that diffraction limitation enters in. Thus, just for curiosity's sake, I wish to run a simple comparison.

My idea is tape some black nylon screen material tightly against the back wall of our fairly smooth, light-colored stucco house and make images at f/16 (which is probably near optimum sharpness for these lenses) /32, and /45 (plus /64 with the 135) from 5-6 feet away.

I know that various lenses are optimized for smaller or greater distances; again, this is very general, and unless one of the lenses really starts losing sharpness at 2-3 feet that could affect such close-ups as I mentioned, which I find highly unlikely, this test, with screening pretty much filling the frame, should offer reasonable comparison of sharpness at the apertures selected.

I know that the enlarger must also be aligned, that it, too, has a lens, and that the photographic process has more variables than a barrel of monkeys. Again, I'm not going for numbers, just planning to poke around, so to speak, to see if the limitation will show up at all, and if so, how much, within my general parameters.

[Bob Salomon]

Those lenses should be optimized for 1:20 which means they should perform well down to 1:10. Closer their performance should fall off. They should also be diffraction limited at f22.
So you could have 2 problems with your tests should you be shooting closer then 1:10 and at apertures smaller then 22.

[Eric Woodbury]

Be sure to read this and the article mentioned near the bottom by Dr Hansma.

https://www.largeformatphotography.info/fstop.html

It is said that optimum f/# for LF lenses, and maybe others that are affordable by common man, is two stops down from wide open. This reduces spherical aberrations certainly. Also, it is about the point where aberrations and diffusion are equal. As you continue to stop-down, the aberrations fade and the diffusion comes on stronger.
Sometimes a little aberration or diffusion is better than 'out of focus', but sometimes not. This is where your experience is needed.

Don't worry about it too much. There are plenty of other things to occupy your mind.

[mdarnton]

If I were doing it I'd shoot newspaper, and I'd shoot at a slight angle to minimize the effect of focus shift (since you'd always be able to find somewhere on the tilted paper that was in focus, focus is out of the problem.) I say newspaper because that kind of high contrast and variable subject can tell you more than I think a screen would.

The best subject is probably the good old resolution test chart, but then you have to be more aware of focus shift and error.

[Dan Fromm]

I wish there were a hard-and-fast rule but it really depends on how much you want to enlarge.

[Jeff Conrad]

Diffraction depends on the effective f-number, so it gets a lot worse in close-up work. I discuss diffraction in detail under “Diffraction” in https://www.largeformatphotography.info/articles/DoFinDepth.pdf. Alas, I didn’t give any examples for close-up photography.

[Ulophot]

Thank you, Bob, and thanks to all.

[Alan Klein]

Since you shoot portraits, shouldn't DOF be an important criteria? Normally, you'd want DOF to extend from the tip of the nose to the back of the head. If you use too open of apertures, you start getting out of focus noses and ears. If you go too small, you start bringing into focus backgrounds. In any case, I don't see how you get into diffraction with DOF used for portraits.

[Alan Klein]

Diffraction may be more of an issue with landscapes where you're looking for maximum DOF's.

[Bob Salomon]

Since you shoot portraits, shouldn't DOF be an important criteria? Normally, you'd want DOF to extend from the tip of the nose to the back of the head. If you use too open of apertures, you start getting out of focus noses and ears. If you go too small, you start bringing into focus backgrounds. In any case, I don't see how you get into diffraction with DOF used for portraits.

We were taught tip of nose to base of ear.

[Doremus Scudder]

IM-HO, depth-of-field always trumps diffraction degradation.

The visible effects of diffraction in a print depend not only on the (effective) taking aperture, but also the degree of enlargement, viewing distance and visual acuity of the viewer. In many cases, the slight overall loss of acutance caused by diffraction may not even be objectionable, depending on the subject and the intent of the photographer.

As far as I'm concerned, even with a worst-case scenario, e.g., a close-up taken at, say, f/45 on 4x5-inch film and enlarged to, say, 11x14, the loss of sharpness due to diffraction is much preferable to annoying out-of-focus areas.

Of course, we always try to optimize sharpness by choosing our viewpoint carefully, using movements, etc. in order to get as close as we can to the magic f/22. However, I don't hesitate to stop down to f/32 or smaller if I need it for DoF. I think I have a lot more photographs made at, or close to, f/32 than any other aperture. I don't see a practically significant loss of sharpness in prints up to 16x20.

Sharpness isn't everything...

Best,

Doremus

[Drew Wiley]

Does that tip of nose to base of ear dogma apply to shots of Jimmy Durante too? Is there some nose-to ear depth of field chart or app, with a nose-length caliper included? Who cares what someone was taught? Great portrait photographers like Julia Cameron and Steichen tended to focus and stop down to the where it simply felt right on the groundglass, esthetically, for them personally. Even the softening effect of diffraction has been deliberately used by some. Conversely, many use out of focus areas deliberately and intelligently. No rules.

[Bob Salomon]

Does that tip of nose to base of ear dogma apply to shots of Jimmy Durante too? Is there some nose-to ear depth of field chart or app, with a nose-length caliper included? Who cares what someone was taught? Great portrait photographers like Julia Cameron and Steichen tended to focus and stop down to the where it simply felt right on the groundglass, esthetically, for them personally. Even the softening effect of diffraction has been deliberately used by some. Conversely, many use out of focus areas deliberately and intelligently. No rules.

But what you see on the gg doesn’t necessarily show you what an enlargement would look like!

[ic-racer]

When I tested for diffraction using my equipment, the relative effects viewed under the enlarger, approximated the results of in-camera tests.

To be more specific. For each format I tested, I could approximate the in-camera effects by watching grain, in real time, under the enlarger lens as the lens is stopped down.

EXAMPLE:

35mm film enlarged with a 50mm lens. Analyzed with a grain focuser. Enlargement to a 'usual' size like 8x10. Right about at f8, the grain starts to get fuzzy. This approximated what my in-camera tests showed.

Similar with 4x5 film enlarged to 11x14 with a 150mm lens. Grain is much harder to see, but seems to get fuzzy around f32.

8x10 is very hard to do the test because grain is hard to see but for a 16x20 enlargement, grain gets fuzzy around f64 and this was similar to in camera tests.

[ic-racer]

I think most of the posters in this thread are pretty experienced photographers know of the the focus method of Hansma,( it is on this foums main page.) Just to emphasize that method is designed to provide the best compromize between airy disk size (diffraction) and defocus (depth of field).

When I first tried it I was convinced it would be a FAIL when apertures were recommended for my focus depth beyond my 'known' diffraction limits I determined in post #14. However as others, like Dormeus pointed out above, the method really does give excellent prints.


the loss of sharpness due to diffraction is much preferable to annoying out-of-focus areas. --D.S.

205852

[Ulophot]

Thanks again to all; I appreciate both facts and feelings. However, I would like to ask one more question, since, not finding the answer in searches, I made a calculation on my own, which is bound to be wrong unless I got lucky. Again, friends, this is primarily curiosity, since my portraiture comes first and, as I said originally, my two lenses are more than adequate.

For illustration, one may refer to two photos from my cited garden work, both posted in the last couple of days (it's July 14, 2020 today), in the "Flowers Anyone?" and "Just Leaves" threads.

Based on Bob Solomon's initial reply to this thread, I am trying to figure out how to calculate reproduction ratio. I am simply trying to have in the back of my mind what subject distance with each lens starts falling below the 1:10 general consideration that Bob mentioned. Am I worried about it? I am not; I am simply curious, and I like to know my equipment. I hope I have emphasized enough that my interest is not not a critical one in this matter.

Here's what I did: If I have a 6' length covered on the long dimension of my 4x5 film, I am reducing 72 inches to 5, approximately. 72/5 = 14.4. Therefore, my magnification ratio is roughly 1:14 at whatever the subject distance is with that lens. If that's right, then, for instance, in my Hydrangea image in "Flowers", a ~4"-long leaf, essentially parallel to the film plane so that it's length is not foreshortened, which measures 1" on the GG, means the ratio is 1:4. With such an approach, I can easily find out subject distance for a given approximate repro ratio.


Am I calculating correctly, for general approximating purposes?

Thanks.

[Ulophot]

Hi, Alan, thanks for your reply. In my portraiture now, my considerations area bit different. I spent years photographing in studio, and when I returned to photography a few years back, I had decided to use natural light, or existing light, as much as possible, and leave the studio for location work, i.e., with my subjects in their own environments. So far, I have tended toward framing which includes more of the subject and something of the surrounds, so that my DOF considerations are different from what often works so well in more head-and-shoulders or closer kinds of framing.

As mentioned in my initial post, it was closer-up photos made in my garden, of plants (which allowed me to photograph without a mask on myself or the plants), that led me to consider the practical effects of diffusion limitation with my particular lenses.

[Bob Salomon]

I used a ruler or a yardstick and measure its length on the gg. But a much easier way is with the Rodenstock DOF/Scheimpflug pocket calculator.