In article <4l9o66$fmk@reader2.ix.netcom.com>, bobgur@ix.netcom.co says...

>---------I once shot side-by-side pictures on the same type of
>fine-grained, very sharp film with a 35 f2 Nikkor ($200), a 35 f2.5 ser
>E Nikkor ($50), and a 35 f3.5 Takumar screw mount ($35). I shot at f8,
>f11, and f16.
>There were no diferences among the negatives when viewed with a 20X
>magnifier, center or corners.

This is not surprising - the differences among good lenses will show
at apertures wider than the ones that are nearly diffraction-limited,
and most good lenses for the 35mm format are near diffraction
limiting by about f8. I use this when comparing and evaluating lenses
without resorting to charts-and-numbers tests - the center at f5.6-8
makes a good reference image for comparing with other parts of the frame, other apertures, or other lenses.
Hope This Helps