Optimizing diffraction and DOF

[feppe]

I've been doing some number crunching to find an optimal aperture for a shoot. It's full length portraits with a Gowlandflex 4x5 and 180mm f/5.6 Symmar S, and the print sizes will be up to 40x50", prints viewed at 1m distance. I need roughly three meter shooting distance and 50-100 cm DOF to fit the model comfortably in the frame, and keeping her sharp from shoulder to shoulder even with profiles.

Plugging in the data to Cambridge In Color's DOF calculator yields required aperture of at least f/22, depending on the eyesight setting. Diffraction calculator claims that I would be diffraction limited starting at f/32.

Given the fuzziness in all of the above, my conclusion is that f/22 is a fitting compromise for full length portraits for medium/large prints with a 4x5. I've shot before with f/16 and have been happy with the results, but the prints have been significantly smaller.

Any comments or disagreement from you who have more experience with large formats?

[David A. Goldfarb]

f:22 is a completely normal, middle of the range aperture for 4x5". It's nothing to worry about.

[IanG]

f22 is also the optimum f stop for most LF lenses.

Ian

[Tobias Key]

F16 or 22 would be what I'd choose to shoot at with requirements you've described. Of course the other side of the coin is if you find yourself shooting with a slow shutter speed what you gain with lens sharpness and DOF you might lose with your subject moving. I would always be wary of going slower than an 1/8th, in that situation I'd rather open up to F11 or even F8, or use a faster film, same if it was a bit windy, I'd look to use the fastest shutter speed I could. Ultimately, unless you in the studio, conditions will have a lot to say about the aperture you can use.

[Jim Jones]

f/64 was the chosen aperture for much classic 8x10 photography. f/32 would be the equivalent for 4x5 format, and f/8 for 35mm cameras. However, DOF is more a matter of personal preferences than mathematical calculations. Many factors such as the lighting and the clothing the model wears should be considered. Better yet, try test photos that simulate the final sittings as closely as possible.

[ic-racer]

You don't indicate what your focus spread is. That is the factor that is needed to calculate the optimum aperture.

[E. von Hoegh]

I need roughly three meter shooting distance and 50-100 cm DOF to fit the model comfortably in the frame, and keeping her sharp from shoulder to shoulder even with profiles.

[vinny]

If you're making such large prints (the hottest thing since the hula hoop) and you're that worried about sharpness, sell that symmar and get a apo sironar-s.

[Kirk Gittings]

You didn't say how you are printing. If digitally then you have sharpening options which will determine how diffraction actually effects the sharpness of the final print. Quality of the scan will actually be a bigger concern than diffraction at those sizes. But F22 will be fine.

[feppe]

Forgot to mention this is in studio with studio flashes, so subject movement is not really an issue.

Thank you for all the help - great to hear that f/22 is a good middle ground for 4x5, and not just theorizing.

You didn't say how you are printing. If digitally then you have sharpening options which will determine how diffraction actually effects the sharpness of the final print. Quality of the scan will actually be a bigger concern than diffraction at those sizes. But F22 will be fine.

These are color slides, so to print that big I'm pretty much stuck with scanning and digital printing AFAICT. I take from your comment that diffraction is not big of an issue at f/32 or perhaps even higher, as that can be... fixed in post. Yes, I said it :P