In article <4km3hi$hnc@nntpb.cb.att.com>, rma@clockwise.mh.att.com says... [most deleted]

>Another "rule of thumb" is that lenses are often sharpest when
>stoped down about 2 stops from their maximum aperture. Like all rules,
>there are many exceptions of course!

Ah, but I wonder when this particular rule of thumb will finally die
off, since the exceptions are legion, and the huge number tempts one
to spawn another rule of thumb: "Ignore the rule of thumb that says that lenses are often sharpest when stoped down about 2 stops from
their maximum aperture, and substitute the one that says that most lenses for 35mm are sharpest (in the center, at least) at f8,
regardless of their maximum aperture or design type".
Hope This Helps ;-)