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

["James Lerch" <jlerch1@tampabay.rr.com>]

I actually did calculate the Coma for this project.  Used the Formulas presented here on the list (Thank you guys!) and a program Called "Correct" by Serge Bertorello.  Unfortunately the program is in French, but fairly easy to understand.  Here's a screen shot of the anticipated Coma near the edge of the Chip, using the Full Aperture :

http://lerch.no-ip.com/atm/coma.gif 

With the full aperture, about 80% of the light from a star will fall on a single pixel. 95% will land on about 5*3 pixels, and 100% will land on 16*14 pixels.  That is of course if I can figure such a beast, But I won't know until I try ;)

I'll probably use this scope to take some pretty pictures, but it's main goal will be Astrometric Observations, which can probably live with the Coma.  My CCD will offer about a Square inch of obstruction, so that's good, but I am a little concerned about thermal effects from it, but we'll cross that bridge when we get there ;)

Take Care,
James Lerch
http://Lerch.yi.org/atm (My Telescope  Construction Webpage)
----- Original Message ----- 
From: "Mutalib Abdallah" <omegatroid@hotmail.com>
To: <atm@shore.net>
Sent: Sunday, December 30, 2001 10:52 PM
Subject: Re: ATM 11.2" F/2 Primary testing questions :)


> 
> 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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