[ATM] AAUUUHHGGG!!!!!! what the &*^% is that?

[Royston_Jeremy at emc.com (Royston_Jeremy@emc.com)]

Hello Matt,
	A long time ago I took some pictures of scratches on a mirror I
made. Do a Foucault test in a dark room with a slit width of about 0.5 mm
and a bright source, then move the knife edge to make the mirror just dark
(or use a piece of 1mm wire instead of the knife edge). You'll see the
scattered light, and the scratches.
Now hang a piece of 1mm wire directly in front of the mirror - this
simulates a diagonal vane, and see how much light is diffracted round the
wire. The mirror edge is also very bright, it's a one-sided wire of infinite
thickness. You'll see that the scattered light from the wire is immeasurably
brighter than that from the scratches, and you won't worry so much about the
scratches.
If the mirror isn't perfectly clean, you can see the dirt on it as well
Remember what Fraunhofer, a famous German optician, said "One looks through
lens, not at them"

Best wishes, Jerry

-----Original Message-----
From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net] On Behalf Of
Matthew L. Brown
Sent: 09 February 2004 18:15
To: atm@atmlist.net
Subject: Fwd: Re: [ATM] AAUUUHHGGG!!!!!! what the &*^% is that?



>As has been said many, many times on this list: it's only a scratch, 
>and
>won't have much of an optical effect, just an effect on your pride.  Star 
>test it (even if it isn't fully figured) and you'll see.  What matters 
>more are large areas that aren't figured properly.


Now if it is a deep scratch and you continue to polish, the edges of the 
scratch will round off, and it'll look terrible under foucault testing.

I'd also be tempted not to go quite so far back in grits.  Maybe 220 or 320.

=Matt





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