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[OM] Mirror lens contrast - was Four new pictures

Subject: [OM] Mirror lens contrast - was Four new pictures
From: "John Petrush" <petrush@xxxxxxxxxxxxx>
Date: Thu, 31 Dec 1998 17:50:18 -0800
My understanding is the central obstruction in a visual design always lowers
contrast, regardless of the contrast of the subject.  My own personal
experience bears this out.  High contrast subjects tend to look a little
flat, low contrast subjects are just plain horrible.

There are multi-mirror designs optimized for photographic only use with very
large central obstructions, around 500f the clear aperature area.  These
astrographs are not for visual use, but are capable of exceptionally fast
f/ratios (< f/4) and outstanding contrast, rivaling that of a refractor.  Of
course, they are also sinfully expensive .....

John P
______________________________________
there is no "never" - just long periods of "not yet".
there is no "always" - just long periods of "so far"

Matthias Wilke <Matthias.K.Wilke@xxxxxxxxxxxxxxxxxx> asked:
>
>>Thanks for the info on this lens - very nice results and surprising
>>contrast for a mirror lens.
>
>Concerning mirror lenses, I have read in the Internet, that they have an
>"anormal" behaviour with regard to contrast. Because of there central
>aperture, they amplify the contrast of objects with high contrast, and they
>reduce the contrast of objects with low contrast. Does anyone know more
>about this ?



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