I dunno if this is 100% correct, from my understanding a poor quality lens
does not suffer any more diffraction than an "ideal" lens, however most
aberrations of that poor lens will be reduced by stopping down. My take is
that for your hypothetical "non-ideal" lens it will always be advantageous
to stop down a bit from the theoretical limit (f6.3) rather than open up a
bit.
...Wayne
>
> Dr. Diffraction says it's all in the diffraction numbers. At 8MP on a
> 4/3 size sensor you get most of the resolution at f/8 but full resolution
of the
> red channel means limiting the aperture to about f/6.3. And that's for an
> ideal (non-existent) lens. So a more practical limit is probably about
f/5.6...
> assuming the lens itself performs well at f/5.6.
>
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