Diffraction and using a small aperture

[timparkin]

One of my old jobs was taking photographs of Army and Air Force Battalions which they would get enlarged to 3 meters wide sometimes and stick at the end of the barracks. I did a bunch of tests on my 4x5 using a Super Symmar 150mm lens at f/11 f/16 f/22 and f/32. The results were scanned at 4000dpi. The f/16 were clearly sharper than the f/11 and f/22. The f/32 was significantly blurry in comparison. We're talking very large enlargements though

I also did a big camera comparison where I looked at the effective reduction in quality of image at various apertures.

at f/16 2/3 4x5 had an equivalent of of 205mp

f/16 2/3 = 205mp
f/22 2/3 = 157mp
f/32 2/3 = 115mp

So you've got a ball park for what stopping down can do to your results. Not many people scan 4x5 at 4000dpi though. I would guess you won't see much difference between f/22 and f/32 if you're scanning at 2000dpi but f/45 will degrade quite a bit. I have in my head that f/22 2/3 is the maximum I would prefer to go to.. f/16 2/3 is optimal. Obviously I'll shoot at whatever aperture gets the shot tough... 115mp is enough for me!!!!

[mdarnton]

Your experience with diffraction is similar to mine, in that there's no arguing that quality changes with f-stop are there, and visible, if one chooses to look, and then you have to decide if you care. I ran all of my 35mm Nikon lenses through my digital Nikon to see how they behaved (this is beautifully easy to check, nearly instantly). Now I know what they can do, and usually, for most pictures, in the most likely printing sizes for me, it doesn't really matter and I don't think about it. But if I'm doing something special, I can consider that aspect, now that I know how it works.

[Drew Wiley]

You're only as good as your weakest link. How many damn times have I said that? Now I know that hard-sharp, relatively high-contrast glossy prints are anathema to Lenny, but I happen to like em! And for me, diffraction is a real and distinctly apparent issue, visible in prints. Now if your film isn't flat in the holder to begin with, or flat in the enlarger carrier, you've got bigger problems to contend with first. But this is a no-brainer to me. Diffraction is a potential issue. And
you do need to print or look at the magnified image with a good focus scope. Judging merely with a lightbox has quite a few pitfalls until you learn the ropes, though it's a start.

[Lenny Eiger]

I say phooey! I don't believe it of a minute. Everyone has to lose all this great depth of field they can get - and for what - a little sharpening applied and its gone!

Yes, I scan my film these days, with a high resolution scanner, at close to 8,000 optical resolution. Diffraction is such as small factor that it should be ignored. I mean jeez, most of the people that scan here are doing it on Epson scanners. That is a far more serious loss of sharpness vs a drum scanner. Yet people muddle thru, learn how to sharpen, and get the results that they feel ok with. Some choose to buy a drum scanner...

Others are using film that isn't TMax or Delta, say FP4+, worse, the 400 speed films like Tri-X or HP5. High solvent developers vs high definition. Or color film in the 400 range. This is also much more of an effect that diffraction is.

I'm not saying diffraction doesn't exist. I'm saying ignore it, and enjoy your depth of field. If you do scan your film, apply a tiny bit of sharpness to it (we all do) and it will go away.

I scan so much film that people shot at 22, and the sharpness falloff is much more serious... I am constantly being asked why their images aren't sharp, and they are, just not exactly all over the image like they want it to be... This diffraction thing is a bad joke, perpetrated on photographers. I'm sure there are lens combinations where its more severe, and digital of course, but not as severe as the ubiquitous loss of depth of field that I am seeing everywhere.

Ignore it!

Lenny

[Bob Salomon]

I say phooey! I don't believe it of a minute. Everyone has to lose all this great depth of field they can get - and for what - a little sharpening applied and its gone!

Yes, I scan my film these days, with a high resolution scanner, at close to 8,000 optical resolution. Diffraction is such as small factor that it should be ignored. I mean jeez, most of the people that scan here are doing it on Epson scanners. That is a far more serious loss of sharpness vs a drum scanner. Yet people muddle thru, learn how to sharpen, and get the results that they feel ok with. Some choose to buy a drum scanner...

Others are using film that isn't TMax or Delta, say FP4+, worse, the 400 speed films like Tri-X or HP5. High solvent developers vs high definition. Or color film in the 400 range. This is also much more of an effect that diffraction is.

I'm not saying diffraction doesn't exist. I'm saying ignore it, and enjoy your depth of field. If you do scan your film, apply a tiny bit of sharpness to it (we all do) and it will go away.

I scan so much film that people shot at 22, and the sharpness falloff is much more serious... I am constantly being asked why their images aren't sharp, and they are, just not exactly all over the image like they want it to be... This diffraction thing is a bad joke, perpetrated on photographers. I'm sure there are lens combinations where its more severe, and digital of course, but not as severe as the ubiquitous loss of depth of field that I am seeing everywhere.

Ignore it!

Lenny

My experience has been that most of that loss of depth of field occurred when people focused on the wrong spot and thus minimized the available depth of field.

[Lenny Eiger]

My experience has been that most of that loss of depth of field occurred when people focused on the wrong spot and thus minimized the available depth of field.

I wouldn't disagree. Lots of people fail to understand how far into the scene they should go - and they also misunderstand when a tilt moves the plane of focus more than they expect, and cuts off the focus at a higher elevation.

Years ago, I got a really good Rodenstock loupe from you - and its been wonderful to really see what's going on.

However, depth of field can help in all of these things. It doesn't fix everything, but having very little depth of field makes all those mistakes worsen.

Lenny

[Bob Salomon]

I wouldn't disagree. Lots of people fail to understand how far into the scene they should go - and they also misunderstand when a tilt moves the plane of focus more than they expect, and cuts off the focus at a higher elevation.

Years ago, I got a really good Rodenstock loupe from you - and its been wonderful to really see what's going on.

However, depth of field can help in all of these things. It doesn't fix everything, but having very little depth of field makes all those mistakes worsen.

Lenny

Enjoy that loupe and treat it well. Rodenstock, as well as Schneider, no longer are making loupes.

[Drew Wiley]

Lenny ... even a sharpness freak like myself also happens to take numerous images where selective focus in the name of the game ... where one arrives at the
correct "look" on the GG, where critical details are put in critical focus, and I don't necessarily want more depth of field in other areas of the scene. Optical facts
and aesthetic choices come into play - so "phooey" on your "phooey" (but not too loud a phooey - don't want to make an enemy of you ... might need your scanning services one of these days!)

[8x10 user]

Diffraction is a big issue in MFD. The highest resolution backs require large apertures and have less depth of field.

A lot of the large format lenses need to be stopped down to F/22 or more for maximum sharpness. Only the best Large format lenses are close to being diffraction limited at F/16. F/22 is a good aperture for most LF work. The theoretical limit for a lens at F/22 is about 3600 DPI

Sharpening can increase the appearance of sharpness but cannot increase the DOF.

Lets say the sharpest chrome films have an average dye cloud of about 8-9 microns. If put into a grid this would be equivalent to ~2800-~3175 DPI. However the dye clouds on film do no appear in a grid but rather are stochastic. There are a few ways to obtain the best possible digital representation of the film. One way would involve scanning the film at an extreme resolution with a sample size much smaller then the film grain. This would yield a file with an extreme amount of noise from "grain aliasing" however it could be possible for the image to be processed (essentially digitally de-screened) in a way that produces a good image. Another way would be to scan the image with an aperture size that is closer to the film grain and then to subsample in order to find the grain edge with more accuracy. This files will also benefit from digital processing only with more of a focus on sharpening rather than noise reduction.

So 3600 DPI might be the limit of resolution at F/22 but a higher resolution scan is helpful to get all of the data.

3600 DPI or ~ a 10x enlargement printed at 360DPI should be close to the limit of the best color films, some films will not hold that much. Some black and white films are able hold more.

At F/32 the limit would be ~ 2540 DPI (Rockwell's numbers x 2 x 25.4), this is still a good number for 5x7 and 8x10s. Large formats are about more then just resolution. There would be less grain and better tonality in a 2540 PPI 8x10 then a 3600 PPI 4x5.

At F/45 (~1780) is where I would think someone would start to notice the difference.

Images from the F/64 club are limited to ~1270 DPI so they would only be good for maybe a 4x enlargement. However that 4x enlargement is going to look very nice with its high DOF and low grain (due to low reproduction ratio). I was talking to a retired commercial photographer who shot 8x10 and he said he used F/64 (for DOF) for everything and it wasn't an issue because the images were only printed to magazine size.

[8x10 user]

I once saw test results from a Leica and ultra high resolution surveillance film that indicated an obtainable resolution of 16,000 DPI. Of course a 2000 DPI 8x10 will have a much different look.