Re: [ATM] Auto Collimation Flat - not cored

["Mitchell R" <funnybone101@embarqmail.com>]

-----Original Message-----
From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net] On Behalf Of
Shane LaPierre
Sent: Thursday, August 09, 2007 10:46 AM
To: atm@atmlist.net
Subject: [ATM] Auto Collimation Flat - not cored

I've got a good 8" optical flat and would like to use it 
as an autocollimator.  It is not coated, and is not cored. 
 I had thought about using it as a reference to make my 
own flat, but is there a way to use it and not aluminize 
it in the center, or remove the coating in the center so I 
can place a knife-edge @ ronchi in the center?  I've also 
thought about getting a good diagonal mirror and just 
moving it 90-degrees off - as in a newtonian.  Let me know 
your thoughts.

Thanks,
Shane LaPierre


At Stellafane there were two auto collimators, Dave Kelly's' and Dick
Parker's. After talking with them for awhile it would seem a cored flat is
easier but it can be done with a secondary mirror to shoot the light off to
the side. 

Catch is you now have 3 mirrors to align, advantage is if you use the
secondary that will be going into the scope, and you know you have a good
flat you are essentially testing all your optics as a system and what you
get in the tester should be what you get in the telescope seeing as you are
testing everything as one.

According to most people there the flat need not be extremely flat, but it
should be smooth without zones and a good edge or those problems will appear
to be on your mirror. 

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