Diffraction. When does it really matter with LF?

[AdamD]

Hi.
I'm not 100% sure this is the right spot for this question, so please feel free to move this. It's a technique thing....

Anyway, when looking at moden digital gear, I believe the generally accepted "fact" is that diffraction starts to creep in at about f/16. For those egale-eyed folks that might be true, but for me, not so much...I can say I see a general softening of the image (again digital here) at about f/22 or so.

I can't say the same for my one and only LF lens which is a Fuji 150mm f/5.6. to me it's super sharp at f/22 and I'm not even sure if there's a problem at f/32.

So, what's the deal here?

Do LF lenses tend to preform well at very small apertures, way better than modern digital gear? Is that just how it is, physics?

Or is diffraction just as prevelent in LF even at f/22 and I just need better glasses and eagle-eye training?

Thoughts??

Thx!!

[Luis-F-S]

Only you can choose between slight diffraction and lack of depth of field. Me? I'll take diffraction!

[Kirk Gittings]

Only you can choose between slight diffraction and lack of depth of field. Me? I'll take diffraction!

I was giving a talk many years ago with Mark Citret, out in CA somewhere on architectural photography (Not commercial but more art/personal AP), maybe it was at the VC Conference in Carmel. We both repeatedly referred to the aperture in many of our 4x5 exposures as f/32. After the talk someone came up to us, somewhat aghast, saying that the diffraction would ruin our images as if at an aperture smaller than f/22 there was some cliff of unacceptable unsharpness you fell off of. Believe your experience. Try it out and see what works for you and your type of imagery.

I really like what Bruce said "Everything in LF is a trade off. If you open up too far you have shallow DOF. If you stop down too far you soften the image through diffraction. Etc.

The bottom line as you'll find eventually,
is to artfully walk all the trade offs."

nice.

[Bob Salomon]

Hi.
I'm not 100% sure this is the right spot for this question, so please feel free to move this. It's a technique thing....

Anyway, when looking at moden digital gear, I believe the generally accepted "fact" is that diffraction starts to creep in at about f/16. For those egale-eyed folks that might be true, but for me, not so much...I can say I see a general softening of the image (again digital here) at about f/22 or so.

I can't say the same for my one and only LF lens which is a Fuji 150mm f/5.6. to me it's super sharp at f/22 and I'm not even sure if there's a problem at f/32.

So, what's the deal here?

Do LF lenses tend to preform well at very small apertures, way better than modern digital gear? Is that just how it is, physics?

Or is diffraction just as prevelent in LF even at f/22 and I just need better glasses and eagle-eye training?

Thoughts??

Thx!!

The smaller the format the sooner diffraction creeps in. The vast majority of modern lenses for 45 are diffraction limited at f22.
Modern digital lenses around 11or 16.

[Dan Fromm]

The rule of thumb is that resolution measured in line pairs/mm is limited by diffraction to 1500/f number. At f/1, the limit is 1500 lp/mm. At f/22 the limit is 68 lp/mm. And so on.

Another rule of thumb is that a print in which 8 lp/mm is resolved will look sharp at normal viewing distance. This has implications for how much a negative can be enlarged.

No enlargement (= contact printing) means that a negative shot at f/187 will appear sharp. Enlarging by 10x means that a negative shot at f/19 or so will look sharp. This is why my 35mm Kodachromes (ISO 25) of flowers shot at 1:1 and f/16 nominal, f/32 effective, look fuzzy when printed 8x10.

The diffraction limit rule of thumb I gave above is a bit lenient. It gives resolution at 0% contrast, resolution with useful contrast is somewhat lower than the rule of thumb suggests.

[Mark Sawyer]

No enlargement (= contact printing) means that a negative shot at f/187 will appear sharp. Enlarging by 10x means that a negative shot at f/19 or so will look sharp.

For large format, this is key. If you're contact printing, (no enlargement of the negative), forget diffraction. It will barely show up at f/256.

This is why my 35mm Kodachromes (ISO 25) of flowers shot at 1:1 and f/16 nominal, f/22 effective, look fuzzy when printed 8x10.

Nitpicking, but isn't 1:1 and f/16 nominal really f/32 effective?

[Dan Fromm]

For large format, this is key. If you're contact printing, (no enlargement of the negative), forget diffraction. It will barely show up at f/256.



Nitpicking, but isn't 1:1 and f/16 nominal really f/32 effective?

You're right. Stupid typo, corrected. Thanks for spotting it and telling me.

[cowanw]

For large format, this is key. If you're contact printing, (no enlargement of the negative), forget diffraction. It will barely show up at f/256.



Nitpicking, but isn't 1:1 and f/16 nominal really f/32 effective?

They are from a light exposure point of view, because light obeys the inverse square law , but does that mean that diffraction, which does not rely on the inverse square law, is the same at 1:1 and f/16 is the same as infinity and f/32. My gut tells me not.

[Dan Fromm]

They are from a light exposure point of view, because light obeys the inverse square law , but does that mean that diffraction, which does not rely on the inverse square law, is the same at 1:1 and f/16 is the same as infinity and f/32. My gut tells me not.

Bryan, your gut is mistaken. See, for example, H. Lou Gibson's Close-Up Photography and Photomacrography, EKCo publication #N-16.

[Bruce Watson]

So, what's the deal here?

...

Thoughts?

Everything in LF is a trade off. If you open up too far you have shallow DOF. If you stop down too far you soften the image through diffraction. Etc. The bottom line as you'll find eventually, is to artfully walk all the trade offs.

What many people have learned before us is that while diffraction limiting makes the entire image slightly softer, DOF works more like a gradient -- sharpness varies across the image. We see the variation in sharpness fairly easily since our visual systems are excellent with patterns.

This is at least partly why the pioneers like Weston, Adams, Cunningham, etc. who founded Group f.64 chose that name. They valued over all focus. That is, they were willing to give up a little entire image softness to get more entire image DOF.

How you personally feel about it is of course easy to test -- all you need do is make a number of identical exposures using different f-stops. Make prints from each, put them up on your "viewing wall" side by side and see what you think. The more enlargement of course, the easier it is to see, which of course points you to another consideration. And there are many more considerations out there.