A Modest Contribution to Dispelling Diffractiophobia

[Ulophot]

The matter of diffraction and its effects on image sharpness comes up here periodically. I thought I’d share a little something on the matter.

Some of us work in in large format partly for the purpose of making very large prints, by which I mean 16x20, 20x24, and considerably larger. For those who do, it may be that every scintilla of sharpness is desired to accomplish the intention. Others of us lack the means to make such large prints, probably wouldn’t make them even if we could, and/or are not as concerned with ultimate sharpness as some others may be, for reasons of subject matter, style, or other considerations. I live in this camp, as primarily a portraitist with a maximum print size of 11x14. Nonetheless, I do photograph landscapes and other types of subjects occasionally, and the diffraction question has, I admit, quietly nagged me despite the sage words of more accomplished members assuring that loss of sharpness from diffraction rarely trumps inadequate depth of field in practical work.

Today I finally made a test. Using a still life concoction of suitable items arranged well within the depth of field at f/16, I exposed one negative at f/22 and one at f/45 on my standard film, HP5+. My developer is D-23. My lens is a 1960s or ‘70s 210mm Komura, a lens with a good reputation but by no means a wallet-stripping super-multi-coated Apo-Sharpenar from one of the top German or Japanese makers. I set up my enlarger with my 80mm Nikkor lens from the 1970s and made 5x7 prints from a section of the two negatives at about 5x, i.e., a 20x25-inch enlargement.

Guess what. Examining the prints close-up by eye, I can barely tell which is which. Only in the type on the little card can I sense that the f/45 images is not quite a sharp. The small, serif type, 8- or 9-point, is in the range of 1/64-inch high on the negative—all perfectly clear in the prints. But what really wiped away any doubt, is that some fine, individual hairs frayed from a microfiber cloth are also clearly visible. Remember that I’m staring from about six inches at a teency-tiny area on what would be a 20x24 print. I hope the scans will at least indicate what is visible in the prints. (By the way, I applied no sharpening to the scans and only adjusted the black point slightly since they are on semi-matte paper.)

So, for those of you coming into LF work, or film work at all, I hope I’ve helped to allay some of your concern about this little corner of the technical aspects of making art. Now you can spend more time worrying about composition, a much more challenging subject, in my view.

The detail images were scanned at 1200 ppi from an area about 1 1/4 inches on the 5x7 prints.

[lassethomas]

So, when in doubt, stop down your lens!

[BrianShaw]

Excellent; Thanks! I never worried at all about diffraction and after reading about it for years, here and elsewhere, thought that I might be missing a key concept. I'm sure that there is a teoretical and measurable effect but never experienced anything very noticable in practical experience.

[ridax]

There are lots of factors diminishing sharpness beside the diffraction. The taking lens aberrations, the film + developer combo sharpness/resolution ability, the film flatness in the holder, the deviation between the ground glass and the film positions, the focusing accuracy, the enlarging lens sharpness - are just a few. The influence of diffraction is noticeable only when it is relatively large compared to all the other factors combined.

F/45 is a very usable aperture in general LF photography. But take the sharpest lens you can get and a very slow high resolution copy film, and the difference between f/22 and f/45 gets much more visible. Stop a (much sharper then the longer focus LF glass) small format 50mm lens to f/45 - and get the sharpness so poor you'd call it inappropriate. Compare f/45 to f/90 in LF (same difference as with f/22 and f/45) with an ordinary lens and an ordinary film, and you also get enough of the difference due to diffraction because at f/90 the influence of diffraction is greater than all the other factors combined.

[Ulophot]

ridax, good points, but your first paragraph made me chuckle. Here I am trying to dispel fears, and you come along to list a host of other anxiety-causing factors!

Fortunately, the considerations in paragraph 2 lie well outside any experience most of us are going to have in our photography. Rare, I am fairly sure, is the 50mm lens for 35mm that stops down to 22 (very vague memory suggests that I might have seen one on an Alpa ages ago), let alone f/45, and although my 210 stops down well beyond the marked f/45 (which, having done this test, I am like to test and mark for f/64, for experiment's sake), f/90 is certainly beyond anything I will need. I am still honing the skill of deciding where to place the plane of focus to optimize aperture.

I have yet to test performance at the marked f/45 and f/64 on my 135mm 7-blade Nikkor, a lens I have barely used yet. Maybe I'll do it with Delta 100, but in any case, I have ushered this particular ghost out of my haunting zone.

[Michael R]

So, when in doubt, stop down your lens!

Yup. Any time I asked a really good, and technically concerned photographer about this the answer was stop down.

Of course diffraction is a real thing so I’m not suggesting shooting a flat wall head on at f/128 but the point is if you need depth of field, it trumps diffraction. Mark Citret had a nice way of thinking about it. If he’s trying to get everything acceptably sharp where lots of depth of field is involved, generally he’d rather have everything slightly fuzzed by diffraction than have certain parts noticeably sharper/blurrier than others. After all when we look at images it’s the impression of sharpness that really matters.

If that’s not good enough, there are always those good old Edward Weston still lives. People fall all over themselves for those, and they are diffracted like crazy.

Depth of field/where to focus, and diffraction can get as involved as one wants (see Merklinger) but ultimately I think it is fairly futile to attempt to figure out “optimal” anything in the field.

[Kevin Crisp]

I stopped worrying about this some time ago. Between 22 and 32 I can tell no difference looking at negatives with a powerful magnifying glass. 22 vs 45, yes, with the magnifying glass I can reliably tell which was which, but the difference is subtle. Would it show up on a print in the sizes I make from the negatives I shoot? No. and absolutely not from a normal viewing distance. People looking at photographs as photographs don't stick their noses up to the prints. Many of us do.

[Sal Santamaura]

...what really wiped away any doubt, is that some fine, individual hairs frayed from a microfiber cloth are also clearly visible...

I'm not sure how that wiped away doubt. Even after all the gyrations it took to get those images on my screen via the Internet and this forum, a quick glance reveals the f/22 version of frayed hairs far sharper than the f/45 version.

Not to say don't stop down when there's no other way to achieve desired depth of field. But diffraction is real, and you've demonstrated that, so the converse still applies. Namely, don't stop down if there's another way to achieve desired depth of field.

[Bernice Loui]

Effects of diffraction is easily visible in the closer up images# 3 then 4. There is a definite reduction in resolution and image quality in these web data via video display images of significantly reduced image quality.

Using a scanner to magnify the film image as a means to quantify and judge image resolution is inadequate method and means.

Ideal optical instrument to evaluate lens image quality projected on film then processes would be a macroscope like the Leica M420 which has sufficient optical performance need for this evaluation.



Or Zeiss Universal Research microscope:


As applied in this previous post using 5x7 Ektachrome, 14" APO artar @ f22, 5x7 Sinar C, E6 processing at The New Lab.. Note the image quality difference at 260x magnification between the Leica M420 -vs- Epson flat bed scanner at 2400 dpi.. Drum scanner likely does better, but will not equal what a Good optical microscope will do.
https://www.largeformatphotography.i...420-microscope

If the exposure of f45 is needed, definitely use f45... but know for certain there will be image quality degradation with zero escape from the way Nature IS.

Do realize one of the prime perks of using a view camera is the ability to do bendiee thy camera, ala camera movements which can go a remarkably long ways to negating using an exposure aperture any smaller than absolutely needed. Essentially, apply ALL needed camera movements at full lens aperture then make a calculated and deliberate choice exposure aperture knowing and fully understanding smaller the exposure, greater the image degradation.

Also notable is the ideology of everything "sharp" in the image belief. All good and great with this, until there is a realization and acceptance that all lenses have a single point/plane of focus with DOF/F appears to be in focus... or the entire "circle of confusion" deal...


Bernice

[Vaughn]

I learn LF photography under the redwoods, where f64 was a dear dear friend who helped me create a little stillness, a little sense, from the chaos. And where one had to keep camera movements to a minimum because there was rarely one 'plane' in the scene that one could align focus with to be of much use.

Once getting out from under the Redwoods, it was difficult for me to break the habit of always f64-ing it. But my 16x20 silver gelatin prints (from 4x5) usually had an increased feel of sharpness taken at f16 vs f64...everything else being equal.

If a photographer was to apply color in just one small area of a B&W photograph, the viewers' eyes would be directed towards the color...and hopefully the photographer had a decent reason to do so. I feel the same way when focusing. If there is an out of focus area in my image, I'd better have a reason for it, and not just because of any limitations of my lens or the rules of optics.

In most images, I prefer everything reasonably sharp. It echos how I believe our brains 'sees' and creates a feel of a place, and I do not want any areas out of focus to distract from the other elements I am working with (light, for example). Unless, of course I am using shallow depth of field or focus as compositional elements.