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Re: 50/2 macro min aperture was RE: [OM] new user

Subject: Re: 50/2 macro min aperture was RE: [OM] new user
From: "John A. Lind" <jlind@xxxxxxxxxxx>
Date: Sat, 20 Nov 1999 09:50:27 +0000
At 07:31 11/20/99 , Acer wrote:
>Ouch... Being a macro, wouldn't it be nice of it went further down, say
>f:32

Ooooh ... that would be nice but would likely cause diffraction problems on
a 35mm format lens with 50mm focal length.

Ever wonder why most 35mm format lenses only stop down to f/16?  There is a
limit to how tight a lens aperture can get before noticeable diffraction
degrades image rendition. The limit is about f/22 with most 35mm format
lenses before diffraction effects approach the size of a largest acceptable
circle of confusion.  For any specific lens design it is related to the
distance from the aperture diaphragm to the film plane which is why some
can (and do) go tighter.  Beyond that point (tighter aperture) how good the
rest of the lens is doesn't matter much, resolution is lost to diffraction.
 This is a major concern for the "pinhole" crowd in determining how small
the pinhole can be.

-- John

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