Originally posted by jeffkrol The bottom line is that even with a 16 Megapixel full frame sensor f/22 is not past the sensor diffraction limit with sharpening.

I actually stopped reading and commenting about this topic. Here, I feel invited to complete the picture.

You are right as far as diffraction is concerned. But of course, this is only part of the picture.

These factors play together when it comes to create a decent computational model of image resolution:

- finite sensor resolution

- lens abberation (can be corrected for low noise)

- diffraction (can be corrected up to the Rayleigh limit, sharpening)

- motion blur (can be corrected, deconvolution)

- out-of-focus blur (can be corrected, deconvolution)

- noise (limiting sharpening and corrections, and digital better than film)

I created such a (yet unpublished) computational model taking the first three factors into account.

I followed the tradition to add abberation powers to end up with an overall abberation power [source: from FujiFilm Professional Data Guide, AF3-141E, 2002, p 129]. Resolution is inverse proportional to abberation power.

From my computational model I was able to eliminate finite sensor resolution and diffraction from publihed lens resolution figures and it turned out that the center resolution due to lens abberation (the ray tracing resolution) can be modelled by the following formula:

*R(raytracing) = Q * f*

f is the f-stop figure (like 5.6) and Q is a lens constant representing a lens optical Quality. Very few best of the best primes have

Q = 120 lp/mm, and very good primes have

Q = 80 - 100 lp/mm (like Pentax FA31)

and so far, I only studied FF SLR primes. Q for zooms would be a lot lower. Beyond 100mm and below 20mm, Q starts to decrease.

So, ray tracing resolution increases with f while diffraction resolution decreases with f. I.e., the higher Q, the lower is the f where resolution maxes out.

Taking all factors into account, I came to the conclusion that 25 MPixels for FourThirds, 40 MPixels for APS-C and 100 MPixels for FF are sort of a sweet spot. A resolution which can be surpassed but where going to the next larger sensor would then be the cheaper solution.