ddb@dec-mrvax.UUCP (06/07/84)
There really is a rationale for using a middle aperture for maximum
sharpness. Exactly what aperture is best varies lens to lens, but in
general there is a tradeoff going on which ends up favoring a middle
aperture:
A theoretically perfect lens performs best wide open. This is because
diffraction in the aperture is the only "abberration" present (it's
unavoidable even in theory). Stopping down a real lens causes some loss
of sharpness due to this diffraction.
However, in a REAL lens there are also other aberrations (maybe I'll
eventually get through all the spellings, one of 'em must be right!),
and they tend to be REDUCED by stopping down.
So, somewhere in the middle, just where depending on how bad the other
abberations are, comes an aperture that's best for any given lens.
In the same posting, Bruce Golab mentioned applying techniques of m
marksmanship to squeezing a shutter release. I actually learned it the
other way around -- I was a photographer first -- bit it works fine in
both cases. I can extend the analogy a bit -- I've used some camera
straps that can be employed the same way a rifle sling sometimes is
to steady your hold. Takes a bit of careful adjusting (in both cases).
-- David Dyer-Bennet
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