Diffraction. When does it really matter with LF?

[Mark Sawyer]

Jim's post reminds me of a little trick I learned from ancient markings on a couple of my old shutters: put little paint/pencil marks on the aperture scale at 1 inch and 1 centimeter. It makes the bellows extension math incredibly simple. 30 cm extension at 1 cm aperture? f/30. 45cm extension at the same aperture? f/45.

For a smaller apertures, a mark for .5 cm is almost as simple.

[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.

[Doremus Scudder]

For me, depth of field trumps diffraction degradation every time.

I shoot 4x5. If I have to stop down a lot, I just reduce the maximum enlargement size I can get from that particular negative. Printing 8x10 from 4x5 film, I can stop way down, even to f/64, and not get objectionable diffraction degradation.

Also, it seems that scenes that need a lot of stopping down are the ones I don't want to enlarge much anyway; things like close-up still lifes, natural details, etc.

One of the big advantages of large format is that one can use movements to optimally position the plane of sharp focus in a scene and thereby be able to use a smaller aperture than one would need without movements to get everything acceptably sharp. Mastering view-camera technique is a real help.

Best,

Doremus

[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.

[cowanw]

The nearest library copy is the centre of Canada, that is Toronto. One day I will get there

[Dan Fromm]

The nearest library copy is the centre of Canada, that is Toronto. One day I will get there

Inexpensive at on-line used book stores.

[Greg]

In the late 1970s and early 1980s I shot a lot of waterfalls in New England with my 8x10 and a 12" Wollensak Velostigmat Series II. All exposures shot at f/64 or f/90. At the time I made contact prints on Varigram or Varilour FB paper. Around 10 years ago scanned the negatives and made digital negatives to print Platinum/Palladium prints from. Loss of sharpness from diffraction is definitely in the original 8x10 negatives if you look at them under a low power X4 Loupe. Holding the prints side by side at arm's length, most people would say, resolution wise, that the FB prints are a tad bit sharper than the Platinum/Palladium prints. Aesthetically and tonality wise, the Platinum/Palladium prints far outshine the FB prints. Several of my friends/relatives are not photographers and when asked which print is sharper, all responded that the Platinum/Palladium print was definitely sharper. When I am doing Photomicrography or Photomacrography diffraction, to me, is a major concern and factor. When I am shooting outside with my 8x10 or 11x14, diffraction matters little to me. The image matters all to me. If I were concerned with loss of sharpness from diffraction, I just might never take out my 8x10 and 11x14 ultraWA pinhole cameras. To me the final image in the final print is what matters the most...
Comments most welcome

[Dan Fromm]

Re Greg's post #17 above, +1. Sharpness is overrated.

[Drew Wiley]

From my own practical needs, I try not to go smaller than f/32 for 4x5 format, or smaller than f/64 with 8X10 film (or smaller than f/45 if a large print like 30X40 inch is in mind). Obviously, I'm referring to enlargements; I rarely contact print.

[AdamD]

Hi all,

Good thread...thank you.

So, I've re-read the thread and here's what I was able to get out of it....

- There are rules of thumb to determine diffraction
- There are generalities that guide users with how to avoid diffraction
- There a school of thought that goes something like this...'so what, just shoot more'
- There a school of thought that understands the compromises involved in photography so pick the one that most important to you at the time of the shot
- Large format affords the user unparalleled flexibility to minimize diffraction, take advantage of it

Pretty good, I can roll with that.

Thanks!!
Adam