Max resolution film size for large format.

[bluechromis]

I have heard people say that for larger than 4 x 5 negatives, there are diminishing returns on increasing resolution (line pairs visible) in prints because of increased diffraction. Is this true? This question is about enlarged prints where the prints are considerably larger than the negative. The question is NOT about contact printing.

 

[koraks]

diminishing returns on increasing resolution (line pairs visible) in prints because of increased diffraction. Is this true?

Factually wrong. Diffraction is a physics phenomenon and relates to the wavelength of the light and the physical size of the aperture used. The wavelength obviously doesn't change. As you go up in film size, you generally use longer lenses with therefore larger physical apertures for the same angle of view and same f/stop. So diffraction will be less. This will be the case for the recording as well as the printing. Another factor is that for the same print size, you obviously need to enlarge a smaller format much more than a larger format negative, so whatever softness from diffraction is present in the negative will show up earlier (at smaller print sizes) for the smaller negative sizes.

Note furthermore that anything from 4x5" and upwards can be enlarged with excellent results to pretty gigantic sizes, so it's kind of a moot point anyway if you ask me. There is a law of diminishing returns in that sense - there's just very little compelling reason for the vast majority of photographers to go any bigger than 4x5. Typical bottlenecks are formed by the two B's - your Back and your Budget.

I suppose that the 'diffraction' story may have to do with the assumption that lenses for larger formats may not be manufactured to the same strict tolerances as those for smaller formats, resulting in the smaller format lenses outresolving the larger format ones despite diffraction (and not because of it). But that's a wild guess on my part.