[ATM] Testing a flat

[jbentz at inreach.com (Jan Bentz)]

 David -- Quite so, but for a quick and dirty qualitative test for 
goodness you can hold the mirror, coated or not, so that the plane of 
the mirror is at eye level.  Look across it toward  most anything at a 
grazing angle.  Compare a known good one with a piece of window glass. 
 You will be able to detect cuvatures and irregularities down to a 
couple of fringes with practice.

  Jan Bentz

David Harbour wrote:

>The Ritchey test is indeed far more sensitive than what this fellow
>suggests, as per the other answers you've gotten from others, as I see
>above. His description of it is found in both the old Albert Ingalls books,
>and also I believe in his 1906 paper on the construction of the 60 inch
>reflector and the making and testing of the mirrors for the 60".
>
>Davey
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>>Is this guy's suggestion reasonable?
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>>Thanks and regards
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>>Adam
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