Re: [ATM] Astigmatism need fixing? And how to do so?

[Jim Burrows <burrjaw@earthlink.net>]

At 2005-02-11 13:50 -0800, J Killea wrote:

>Along the better axis, I am at 21nm PV (surface), and along the other 
>axis, PV= 45nm.  Also of concern is that along the poorer axis, b = 
>-0.761, versus -0.941 on the better axis.  If I were an expert, I would 
>probably dive in for one more time around the barrel to see if I could 
>make things better; but several questions jump to mind (aside from the 
>fear of setting myself way back):
>
>1)  Do these measurements indicate significant astigmatism? ( I am not 
>planning on using the scope for anything even as fancy as 
>photography).  It would be a while before I could actually do a start 
>test, since I don't have easy access to an 8" Newt currently  (OK, maybe a 
>salamander).

Forget about the PVs - they don't count, and astigmatism is a parallel 
universe to Foucault and something to worry about later when the mirror 
cell is made/bought.  The averaged readings give surface RMS 8.5±3.8 nm: 
keep the mirror away from any pitch lap - you're DONE (except, if you can, 
a second opinion star test).

         -- Jim Burrows
         -- mailto://burrjaw@earthlink.net
         -- http://home.earthlink.net/~burrjaw
         -- Seattle N47.4723 W122.3662 (WGS84)  

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