Can you provide some documentation or evidence that the pixel density of the sensor has no effect on the aperture at which diffraction affects image sharpness?
Let me try this argument, which I hope is based on assumptions that we can agree on. 3 points make the argument (which is by no means original):
1) The sharpness, more precisely the MTF, of the system (camera+lens) can be expressed as the product of exactly 3 factors: a
) MTF curve describing lens aberration excluding diffraction,b
) MTF curve diffraction (not quite a simple as the correct formulae kindly given by Canon-F1 would suggest)c
) sensor MTF.
Note: as usual for MTF curves a
are all functions of spatial frequency (normally declining with frequency).
are functions of the aperture (as well as spatial frequency). We all know that factor a
usualy improves as the lens is stopped down quite quickly at first, then more slowly (from f/4 or so for most decent lenses).
We also all know that factor b
follows the inverse relationship hinted at by Canon-F1's Rayleigh criterion - but that is only one point on the curve. I suspect the most important point is that some (perhaps little) contrast remains to much higher spatial frequencies (and yes, there are nulls where there is no contrast at all, for one color of light at a time).
All I claim is that factor c
does not depend on the f/no. (which seems self-evident to me)
3) The product of a x b x c
therefore has a maximum determined by max(a x b
) and is scaled overall by c
. A "perfect" sensor will have c = 1 at all spatial frequencies, and so the MTF is just a x b
any lower pixel count sensor (with a smaller value of c
independent of f/no.) gives a smaller product at any f/no. (QED)
I believe that anyone who thinks I'm mistaken has to disagree with one of the 3 points (and it would be good to know which), or we have a purely semantic disagreement (most likely due to the 100% viewing when the image gets bigger as the pixels get smaller - that is not the situation I'm describing!).
ps. Seeing another post by Canon-F1. The pixel / Airy disk illustration given by Sean McHugh is seriously
misleading I know that many many people have been misled by it. Sampling theory tells quite a different story. It is best to calculate using MTF in the spatial frequency domain, as suggested above.
pps. not even neutrinos go faster than light
never mind spaceships.
ppps. there seems to be a bug that prevents me from italicizing one of the "c"s.