Re: [ATM] Mirror back from coaters with scratches

["Thomas Janstrom" <thomas@moiler.com>]

Hi Hiroyuki,

Scratches are quite obvious under the Foucault test, so you would have
noticed a scratch(s) of this size when you were testing.

The shape of the scratch, being S shaped, makes me think it is a result of
clean the mirror, so the coaters most likely put it there. Now you have two
options, complain and try to get them to re-coat it for free after you
polish the scratches out, and option two repolish and spend the extra 50 on
a better coating service provider...

If the scratches were smaller I would suggest ignoring them, the secondary
mirror vanes will cause diffraction effects that will appear for all intents
and purposes as huge scratches anyway, but with a 6" mirror you WANT it as
good as it can be.

Cheers, Thomas.

-----Original Message-----
From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net] On Behalf Of
Hiroyuki HIKITA
Sent: Friday, 25 August 2006 2:40 AM
To: atm@atmlist.net
Subject: [ATM] Mirror back from coaters with scratches

Hi all!

Lots of wandering through the ATM archives and sheer luck,
my second attempt to make a 6" F6 mirror came out very well
with a smooth surface and Waveerror P/V 1/20 Lambda.

Two weeks ago I sent out my second mirror to the coaters.
Today my 6inch F6 mirror came back from the coaters.

Lesson: NEVER use a cheap coater just to save $50...

The mirror came back with several S shaped scratches about
2"x1" in size.

So my question is:
1) How obvious are scratches this size under the Foucault test?
   Could I have missed it under the knife??

2) Is there a quick way to tell if the scratches went all the way to the
glass?

# Hiroyuki HIKITA <hikita@tkb.att.ne.jp>
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