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Re: [OM] Generic lenses for Oly OM equipment

Subject: Re: [OM] Generic lenses for Oly OM equipment
From: "Ian M. Stewart" <ims@xxxxxxxxxxxxxxxxxxx>
Date: Wed, 25 Feb 1998 12:29:36 +0000
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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