At 10:21 24/02/98 -0600, contributors wrote:
>>> The diffraction limited cut-off frequency of a lens is given by
< snip a complex formula >
>>
>>Independent of Magnification so far only for the "real or effective
>>aperture"
>>For example: choosen aperture = 5,6 effective aperture at 1:1 = 11
>A simple focal length/4
>formula that is often given is just as effective for photography. In this
>case 90/4 yields f/22 as the minimum stop to prevent image loss from
>diffraction.
Help! Does this mean that my 28mm lens should not be used stopped down at
f16 etc? In fact when I'm using it close up with extension, f8 would be
inappropriate - the magnification having changed the *effective* aperture
to something smaller?
Because I'm using the lens so close, and I'm using my T20 flash (on an
OM10), I have to use the aperture recommended to get the correct exposure.
--
Ian <IMS>
OM Tyro - please point my lens in the right direction.
mailto:ims@xxxxxxxxxxxxx
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