I agree that f/22 optimizes the sharpness across the field, but it does so at the cost of absolute sharpness in the center. Check out this mtf graph of a tele-xenar (tessar design) from Schneider:

http://www.schneideroptics.com/pdfs/...56_250%202.pdf

and look at the last two graphs showing mtf from f/11 and f/22. The f/22 is more uniformly sharp across the field, but absolutely less sharp in the center than at f/11. The difference is so small that it is of no practical consequence, but the fact is that if you want the sharpest possible image in a subject in the middle of your frame, you would be better off shooting at f/11 than at f/22, even with a tessar. But again, in practical terms, it is of no consequence, unless you are shooting with tech pan on your 4x5.

Quote Originally Posted by Ian Grant View Post
Clay, the Tessar's were designed to give maximum sharpness & resolution at f22, somewhere I have the figures from Doctor Optic who were the last manufacturer of the CZ Jena designed Tessar's, resolution tailed of significantly after f32 due to diffraction for the135mm/150mm lenses.

Ian