In article <328186F9.1BE3@facstaff.wisc.edu>, ggprice@facstaff.wisc.edu says...
[about Pop Photo's standards for SQF - rest of informative
and excellent post deleted for space reasons, alas....]
>"A picture's center is usually the most important area. It's the first
>place we generally look. We usually place the subject at or near the
>center. But in terms of overall picture area, it represents a small
>section of the photograph. To balance out these factors, central
>(on-axis) MTFs account for 50 percent of our overall picture-quality
>ratings. If we move out to about halfway toward the corners of the
>image field, we still have an important picture area, so we assign it
>over half of the remaining 'quality percentage,' or about 30 percent
>overall. Since the corners represent less picture of area of somewhat
>lesser importance, they account for the remaining 20 percent of the
>overall picture-quality rating (it's measured at 80 percent of the
>distance to the corners)."

Hmmm, the above would indicate that a lens with superb central area
MTFs but absolutely useless corners (and poor edges) could still get
a high SQF rating in Pop Photo - something I have suspected to be true,
given some cheap zoom lens scores... BTW, I may be old fashioned, but
I still consider a lens that is incapable of decent corner sharpness
at a given aperture to be unacceptable at that aperture - the lens
doesn't cover the format for which it was intended at that aperture.
Giving a lens with poor corner/edge performance a high SQF rating is
kinda like saying a car is in really excellent condition, since only
the bumpers and most of the paint are missing...;-).
Hope This Helps