Diffraction?

rayonline_nz · Dec 15, 2014

What are your views on this topic? For 35mm format, don't stop the lens further than F8? If need be use a filter to cut the light out? Having seen those who do shoot at F11, F16 or even F22 - is it that bad? There also may be times when one wants a deliberate slow shutter for creative effects, do you simply just pop on a filter?

gone · Dec 15, 2014

To be honest, I have yet to see any problems with shooting stopped down all the way on anything I've ever shot. Oh, I guess if I looked at the prints w/ a loupe, but who does that? For the modest size that I print, haven't had any issues.

Dan Fromm · Dec 15, 2014

Arrgh! After the lens has been stopped down enough that diffraction swamps the residual aberrations, diffraction limits image quality in the negative. Whether image quality in the negative limits image quality in the final print depends on how much the negative is enlarged. This is why large format photographers who contact print can get away with using teeny tiny apertures (as small as f/128) and 35 mm photographers who enlarge much can't.

If you don't specify how much you intend to enlarge you can't even think sensibly about diffraction.

Rick A · Dec 15, 2014

Hmm... I've shot 35mm images with apertures as small as f22 and enlarged to 16x20 with no apparent diffraction. I'm not saying it doesn't or can't happen, but I feel it doesn't happen as much as people think, and other factors cause the issue and it is blamed on diffraction. I have been ready to blame it on that, but then reflect on the shooting situation and realize it was camera shake or related to operator error. Even on a sturdy tripod there can be vibrations that may be mistaken for diffraction.

summicron1 · Dec 15, 2014

rayonline_nz said:
What are your views on this topic? For 35mm format, don't stop the lens further than F8? If need be use a filter to cut the light out? Having seen those who do shoot at F11, F16 or even F22 - is it that bad? There also may be times when one wants a deliberate slow shutter for creative effects, do you simply just pop on a filter?

diffraction causing troubles is a factor of the actual physical size of the hole the light is going through -- if the hole is very tiny (f-16 on a 21mm lens) than the diffraction pattern is big enough, relative to the size of the light waves passing through the hole, to cause some problems.

For larger lenses the f-16 lens opening is still big enough to not cause problems.

Many lenses DO operate best at f-5.6 or thereabouts because that's the sweet spot for a larger number of optical reasons than just diffraction.

Generally speaking, I don't worry about it.

JackRosa · Dec 15, 2014

f/128 not so tiny

Dan Fromm said:
Arrgh! After the lens has been stopped down enough that diffraction swamps the residual aberrations, diffraction limits image quality in the negative. Whether image quality in the negative limits image quality in the final print depends on how much the negative is enlarged. This is why large format photographers who contact print can get away with using teeny tiny apertures (as small as f/128) and 35 mm photographers who enlarge much can't.

If you don't specify how much you intend to enlarge you can't even think sensibly about diffraction.

Remember ... f/22 or f/128 or f/whatever is the ratio of diameter of diaphragm opening to focal length of lens. f/128 with a 360mm lens (large format) is not as tiny as you would think. You might be surprised how close f/128 with a 360mm lens is to a f/22 with a 50mm lens.

rayonline_nz · Dec 15, 2014

Dan Fromm said:
Arrgh! After the lens has been stopped down enough that diffraction swamps the residual aberrations, diffraction limits image quality in the negative. Whether image quality in the negative limits image quality in the final print depends on how much the negative is enlarged. This is why large format photographers who contact print can get away with using teeny tiny apertures (as small as f/128) and 35 mm photographers who enlarge much can't.

If you don't specify how much you intend to enlarge you can't even think sensibly about diffraction.

A4 or Super A3 ..

Nathan King · Dec 15, 2014

rayonline_nz said:
What are your views on this topic? For 35mm format, don't stop the lens further than F8? If need be use a filter to cut the light out? Having seen those who do shoot at F11, F16 or even F22 - is it that bad? There also may be times when one wants a deliberate slow shutter for creative effects, do you simply just pop on a filter?

There are times when the extra depth of field or lower shutter speed is much more positive impact on the image than diffraction has a negative impact. Honestly, I tend to print small by modern standards and have never noticed degradation that I can see with an unaided eye.

MattKing · Dec 15, 2014

If you have a choice of apertures, use something near the middle.

If other factors push you toward the smaller apertures, accept the circumstances and use them.

SchwinnParamount · Dec 15, 2014

When diffraction rears it's ugly head, it can ruin your day.
I drove from Seattle to Jackson WY in one day last year. I exposed 15 sheets of 8x10 using a couple of older long lenses. Just because AA did it, I thought I could do f64. With all of my lenses, f64 gives me wonderful DOF, but the diffraction under a loupe breaks my heart. Even when I contact print, the effects of diffraction are enough to give me the impression that my negatives are not sharp.
Matt, you're right. Maximum DOF at the expense of sharpness is a bad trade off.

Dr Croubie · Dec 16, 2014

I saw a really good online DOF calculator once. It went a step further than the others and let you specify neg size, print size, and viewing distance from the final print, then told you what aperture you could get away with without too much visible degradation. If anyone knows which one I'm talking about, BTW, I'd love to know where it lives because no amount of googling can let me find it again. And FWIW, I've shot f/22 on my d***l (well past the DLA of about f/6) and printed it on a 4x6" postcard. Didn't look much worse (if at all) than a 4x5" neg (also shot at f/22) that I contact printed, I wonder why...?

LJH · Dec 16, 2014

Have a look at the Apple app "Photobuddy".

ic-racer · Dec 16, 2014

rayonline_nz said:
What are your views on this topic? For 35mm format, don't stop the lens further than F8? If need be use a filter to cut the light out? Having seen those who do shoot at F11, F16 or even F22 - is it that bad? There also may be times when one wants a deliberate slow shutter for creative effects, do you simply just pop on a filter?

If you own a 35mm camera you can expose some frames of the same scene at various apertures and see which aperture you like best.

RalphLambrecht · Dec 16, 2014

rayonline_nz said:
What are your views on this topic? For 35mm format, don't stop the lens further than F8? If need be use a filter to cut the light out? Having seen those who do shoot at F11, F16 or even F22 - is it that bad? There also may be times when one wants a deliberate slow shutter for creative effects, do you simply just pop on a filter?

good question.I had a friends who's images I always admired for their sharpness and I tried to get there myself.I tried every trick in the book,tripod,self-timer,mirror lock-up,fine-grain film,stand development,expensive lenses but I just couldn't get it as sharp as his until he toldmethat he always tries to stay under the diffraction limit.Since then, I keep my exposures between f/8-11, regardless of lens and get much closer to a perfectly sharp image, not ignoring my previous strategies of course.

RalphLambrecht · Dec 16, 2014

Rick A said:
Hmm... I've shot 35mm images with apertures as small as f22 and enlarged to 16x20 with no apparent diffraction. I'm not saying it doesn't or can't happen, but I feel it doesn't happen as much as people think, and other factors cause the issue and it is blamed on diffraction. I have been ready to blame it on that, but then reflect on the shooting situation and realize it was camera shake or related to operator error. Even on a sturdy tripod there can be vibrations that may be mistaken for diffraction.

a sturdy tripod maybe worse than a damped tripod. The unavoidable vibration energy has to go somewhere,otherwise,It will shake the camera eventually.You could bolt your camera to a mountain;that doesn't make the mirror slap go away.placing your tripod legson foam might.

Hatchetman · Dec 16, 2014

This page has the diffraction calculator toward the bottom: http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm

Also note the diffraction calculation is independent of the focal length.

SchwinnParamount · Dec 16, 2014

According to that diffraction calculator, f.64 on my 8x10 camera cannot produce a diffraction effect. My eyes tell me that's not correct. If the calculation is correct then it means that the non-sharpness in my negative is due to vibration. That's a little odd in that my tripod is very sturdy, I was using a cable release with lots of slack, and there was no wind. Is it possible for a shutter to introduce significant vibration when it fires?

desertrat · Dec 16, 2014

SchwinnParamount said:
When diffraction rears it's ugly head, it can ruin your day.
I drove from Seattle to Jackson WY in one day last year. I exposed 15 sheets of 8x10 using a couple of older long lenses. Just because AA did it, I thought I could do f64. With all of my lenses, f64 gives me wonderful DOF, but the diffraction under a loupe breaks my heart. Even when I contact print, the effects of diffraction are enough to give me the impression that my negatives are not sharp.
Matt, you're right. Maximum DOF at the expense of sharpness is a bad trade off.

I've contact printed a few 8X10 negatives made with a 12" RR at f64. Near the center of the field where a RR works best, I thought I could detect a trace of diffraction softening with a loupe, compared to negatives made at f32, but the prints held finer detail than I could see with my naked eye at a normal viewing distance. At the edges there was a hint of softness, but that's what an RR does.

You mentioned you were using long lenses. I wonder if there were other issues going on that might cause softness, like vibration maybe. Did these same long lenses give good sharp images at larger apertures?

I don't remember if it was here of the LF forum, but a member posted images from 4X5 negatives made at f22 and f64 if I remember correctly, and the images were enlarged a great deal. The main difference (visible on a monitor, anyway) was the f64 images were lower in contrast. The amount of detail seemed about the same.

RalphLambrecht · Dec 16, 2014

SchwinnParamount said:
According to that diffraction calculator, f.64 on my 8x10 camera cannot produce a diffraction effect. My eyes tell me that's not correct. If the calculation is correct then it means that the non-sharpness in my negative is due to vibration. That's a little odd in that my tripod is very sturdy, I was using a cable release with lots of slack, and there was no wind. Is it possible for a shutter to introduce significant vibration when it fires?

unlikely.the masses in motion are very small,although ,they move relatively fast,my guess is still 'no'.

Hatchetman · Dec 16, 2014

if the aperture is that small, the shutter speed is so slow, the initial shutter vibration would only represent a tiny part of the exposure -- I doubt it would cause much blurriness.

Dan Fromm · Dec 16, 2014

SchwinnParamount said:
According to that diffraction calculator, f.64 on my 8x10 camera cannot produce a diffraction effect. My eyes tell me that's not correct. If the calculation is correct then it means that the non-sharpness in my negative is due to vibration. That's a little odd in that my tripod is very sturdy, I was using a cable release with lots of slack, and there was no wind. Is it possible for a shutter to introduce significant vibration when it fires?

What exactly do your eyes tell you? What did you examine, and how?

I ask because the diffraction limited resolution in cy/mm or lp/mm is approximately 1500/f number. For f/16 the best resolution attainable (at very low contrast) is 1500/64 = 23 lp/mm. At reasonable contrast you'll get at best around 12 lp/mm. This is plenty for contact printing but the negative will look very soft if examined with a magnifier more powerful than around 1.5x.

The calculator uses a .24 mm CoC for 8x10. This is much larger than conventional and makes it give the wrong answer. For contact printing the CoC can't be larger than .125 mm. Perhaps the person who coded the calculator and loaded its little tables had reductions, not contact prints or enlargements, in mind.

wiltw · Dec 16, 2014

Dan Fromm said:
What exactly do your eyes tell you? What did you examine, and how?...The calculator uses a .24 mm CoC for 8x10. This is much larger than conventional and makes it give the wrong answer. For contact printing the CoC can't be larger than .125 mm. Perhaps the person who coded the calculator and loaded its little tables had reductions, not contact prints or enlargements, in mind.

It also needs to be kept in mind that most DOF calculators (and probably diffraction calculators as well) use what is termed 'manufacturer standard' assumption of human visual acuity, whereas the 20/20 vision standard (in the US) is actually about 3x as good as the manufacturer assumption. For example, if I shoot 8x10 at f/22 and focus at 10', most DOF calculators tell that your DOF zone is from 16" to Infinity; using 20/20 vision, DOF zone is from 38" to Infinity.

John Koehrer · Dec 16, 2014

From Hatchetman's link and under the heading "note on real world photography"

"Even when a camera system is near or just past its diffraction limit, other factors such as focus accuracy, motion blur and imperfect lenses are likely to be more significant. Diffraction therefore limits total sharpness only when using a sturdy tripod, mirror lock-up and a very high quality lens"

Jim Jones · Dec 16, 2014

An important factor that DOF calculators fail to consider is subject matter. Some subjects demand high resolution; others do not. For example, Edward Weston's iconic Shell, 1927, may have been captured with a Rapid Rectilinear in a modified shutter that permitted stopping down to a very high f/number. This number would be effectively increased further due to the lens extension required for this macro photograph. My Cole Weston contact print exhibits good sharpness from the near to the far parts of the chambered nautilus. Nowhere is the image perfectly sharp, characteristic of diffraction limitation. One needs a magnifier to see such a lack of sharpness that would be obvious in a subject with contrasty fine detail. Using a magnifier was only for purposes of this discussion. It would normally be a hell of a way to enjoy Weston.

SchwinnParamount · Dec 16, 2014

Hi Dan, rather than describing what I am seeing, I'll just do a hi-rez scan of the neg and crop the nasty part to upload. People who have more experience with diffraction than I have will be able to judge the issue.

Diffraction?

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