On Wed, 24 Jul 2002 13:13:16 GMT, Carl Solomon wrote:

>I had either read, heard, or been taught (or maybe I just dreamed or
>misunderstood this)...that a given lens will render its sharpest image
>at about one stop down from wide open. Yet when I see award winning
>shots in photo magazines, they are often exposed at stops like f/16,
>f/22, etc. even in scenic shots where depth of field is not an issue.
>Did I just get it backwards?

This (and the more accurate 2-2.5 stops advice) is hooey.
Most good lenses for 35mm reach best resolution around
f5.6 to f8 *in the center*, and sometimes at much smaller
stops in the corners. (Optimum stops for resolution with
larger format lenses are generally at smaller stops.) With
lenses, optical problems generally are lessened as the lens
aperture is reduced - but all lenses are subject to the
resolution limits imposed by diffraction, and this effect
reduces the maximum possible resolution for a given aperture
and FL. So, as the lens aperture is stopped down, the lens
generally improves until it reaches diffraction-limited
resolution, after which resolution goes down with further
stopping down (some optical problems may prevent the lens
from reaching diffraction limits within the given aperture
range, though...). For an example of this, go to:
www.David-Ruether-Photography.com/diffraction.htm, a test for
diffraction-limiting of a very good Mini-DV camcorder lens.
Note the subtle detail changes with the different stops
used (a good range of stops will produce good results with
most good lenses, with f4 [or wider] through f16 generally
still OK for critical 35mm use if the image corners hold
up well at the wider stops...).