On Wed, 28 Oct 1998 22:02:26 -0500, "Ed" wrote:

>Is there a way to determine the aperture value for a given lens
>that will provide the sharpest photograph?

Yeah, testing.....;-)
But, be aware that meaningful testing is not so easy as it would
appear to be...
And, many lenses, especially very fast ones, and zoom lenses,
vary considerably in their performance with both focus distance
and with focal length with zooms, in addition to aperture...
Also, if reasonable sharpness in the frame corners is your
standard for good sharpness (it is mine...), you will often
come up with a different answer than center-only performance
will give.
And, puh-leeze ignore that useless chestnut, "best at two stops
down from wide-open" - it usually doesn't work except for f4 lenses!
Without testing, with high-quality lenses, a reasonable assumption
is that performance peaks in the center around f5.6-f8 for
non-extreme lenses for the 35mm format (BR's mysterious findings
notwithstanding... [I know he is a careful tester, which leaves
me completely mystified by his findings, which are so different
from mine, and from those of virtually all other testers...]).

If you do want to test casually, try running a detailed horizon
line diagonally across the frame from corner to corner. Carefully
(manually) focus. Without changing focus, shoot the same thing at
all the available stops (compensating with the shutter speed to
keep the exposures constant). Try the widest three stops again, with
refocusing done for each set (do NOT assume that marked infinity
on the lens is truly infinity-focus!) to see if you are checking
focus accuracy or the lens... Use good tripod technique, or
hand-holding with fast enough film and bright enough light to
give you sufficiently fast speeds at all stops. Inspect the film
directly, using a good 10X magnifier.
DO NOT get caught up in "tester's disease"! ;-)