Re: ATM 11.2" F/2 Primary testing questions :)

["Mutalib Abdallah" <omegatroid@hotmail.com>]

You seem to be going to a lot of work to make this mirror; why haven't you 
CALCULATED the coma to see if it will be a problem?   I have seen the 
formula in the archives, so you should be able to find it.

Also, have you considered how many centuries of polishing will be required 
to parabolize this monster?   Perhaps you need a way to grind a parabola 
instead of a sphere.   I don't know how to do it; I just know it won't be 
easy.


>From: "James Lerch" <jlerch1@tampabay.rr.com>
>Reply-To: "James Lerch" <jlerch1@tampabay.rr.com>
>To: <atm@shore.net>
>Subject: ATM 11.2" F/2  Primary testing questions :)
>Date: Sun, 30 Dec 2001 15:39:32 -0500
>
>
>Greetings all,
>
>Construction has began on my 11.2" F/2 Dedicated CCD scope (CCD chip 
>resides where secondary mirror would normally be)  I plan on stopping the 
>primary down to F/2.5ish (most-likely) if coma becomes a problem.
>
>While Trepanning and Hogging, I've been pondering the following questions, 
>and would appreciate some input from the group.
>
>#1  Just where do you measure the Roc on such a beast?  The difference in 
>ROC between zone 1 and Zone 7 will be nearly 0.325" (8.25mm)  on a moving 
>source tester.  With this fast of a primary, +/- 0.325" in ROC makes a 
>fairly substantial difference on the Strehl Ratio.  I "Assume" the roc 
>would be relative the Zone 1, but just wanted to make sure....
>
>#2  With such a Fast Primary, I assume Foucault testing will be 
>unsuccessful.  If so, would the Wire test be more appropriate?  Does anyone 
>have a Web reference to the setup of a wire Tester?  If the Wire test is 
>still inappropriate, I guess that would leave me with the Hartmann test or 
>the Caustic test?  I've done a Harmann test with good results on more 
>"Normal" mirrors, and I believe my current test platform will be sufficient 
>for the caustic test,  I'm just looking for some guidance on which might be 
>best/easiest ;)
>
>I guess that's it for the moment, its time to go back to hogging while I 
>look forward to your replies :)
>
>Take Care,
>James Lerch
>http://Lerch.yi.org/atm (My Telescope  Construction Webpage)
>
>




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