In article
>In <5ajfck$jj8@newsstand.cit.cornell.edu> d_ruether@hotmail.com (Bob Neuman) writes
[most deleted]
>>BTW, this effect is also clearly
>>visible when photographing bright sun reflections on water at small stops.
>>Makes one wonder about how wonderful a lens could be if optimised at maybe
>>f2.8-4, removing much of that diffraction-caused point spread for each
>>subject point rendered by the lens...
>Oh, but most f1.4 lenses have their optimum performance at f4-f5.6!
Yes (in the center, anyway [the corners are a different story], and
this is probably more due to the relative ease of designing/making normal lenses, than to the [erroneous] rule of thumb of performance peaking at
2-stops down from wide-open...;-).
>It appears to me that the more tele a lens is, the less problems
>diffraction at the aperture edges gives, since it is the absolute
>size of the diaphragm that matters. Wide-angle lenses should behave
>worse in this respect.
I have heard this before, but in lens checking it strikes me as notable
that virtually all good lenses from 8mm to 400mm or so perform remarkably
similarly in the center from about f5.6 on down through the smallest stops,
indicating diffraction limiting being related to relative aperture rather
than to absolute aperture... (DJ? Comments? ;-)
Hope This Helps