Absolutely true if it's a poor lens and because of other aberrations
does better at some other aperture (not necessarily smaller). The point
about diffraction is that it is based on a perfect lens. The
diffraction limited resolution at any particular aperture can't get any
better than the ideal lens.
Chuck Norcutt
On 12/19/2012 1:01 AM, Wayne Harridge wrote:
> 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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