scyrene said:
It bears repeating because this appears to be a widely-held misconception: if your output/viewing size is fixed, an increase in resolution will *NOT* increase the effects of diffraction. If you shoot at 20MP and 50MP, same format, lens, settings etc, and output to e.g. A3, diffraction (and camera shake etc) will be *identical*. It is only a *potential* problem viewing 100%, crop more on the higher res file, or if you output the higher res file to a larger size.
Increased file size is a completely legitimate concern with higher resolution sensors, however.
I know what you mean, I studied physics and it's therefore pretty sure that I just by training know more about optics than you (sorry, I don't want to be arrogant). But I do not want to talk about wave optics & diffraction basics, Airy discs, and pixel sizes. I made my statement just from the perspective of real life usability, from a non-studio photographer's perspective. A 22-24 MP 35 mm sensor is for many settings the best choice because you simply don't have to make up your mind about diffraction, micro movements etc. that quickly degrade the real optical information you get out of your high MP beast with such a small sensor, if the setting isn't optimum (optimum means studio with big flash system delivering a lot of light, or a tripod and a pretty static motif or long enough exposures). And the 5D series originally was intended by Canon to be reportage cameras, so they were designed for use in non-optimum settings.
So it's simply about what 35 mm photography is made for, and when it gets too pimped IMO. If I need 50 MP I go for mid format, because then I can get non-crippled high resolution images even with closed apertures and large DOF. In fact I do this frequently with my Mamiya 6 system. 50 MP scans with a good film scanner (if I don't want chemical prints) from a fine grained film are pretty amazing, even at f > 10, simply because the 60 mm x 60 mm image area collects a lot of optical information without being too prone to diffraction softening. This size is about 4 times bigger than those tiny 35 mm images! It even dwarfs the new Hasselblad X1D's 50 MP sensor size (43.8 mm × 32.9 mm) that already makes much more sense in terms of photographic versatility than a 50 MP 35 mm sensor.