To: "Bill Kelley"
,,
        
From: Mark Suchting 
Reply-To: Mark Suchting 


At 03:36 PM 6/3/2003 -0700, Bill Kelley wrote:


>  A fully parabolized fast mirror of that
>size
>should not show  much difraction on one side when under Foucault test.
>The test should show the classical "doughnut" shape quite
strongly-thus-
>from the 70% zone out the mirror edge will look turned down.

David

The diffraction ring might also be swamped by the light from the parabaloid
`donut' at COC, considering how `fast' your mirror is. . Testing the mirror
with a knife edge in a Null test may well show that your diffraction ring
is even and intact. I find in figuring ( under Null ) that a nice even 
diffraction ring will pop out only in the last figuring spells ( a bit like
the `diamond ring' suddenly appearing in a Solar Eclipse).

Mark Suchting

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