Re: Re[2]: ATM 10in. Mirror--Star Test ?'s

["John A. Volk" <103037.3107@compuserve.com>]

<What do you guys mean about the star test? >

The star test is the simplest, yet one of the most sensitive optical tests.  
It basically involves examining the diffraction rings of a star image inside 
and outside of focus.  The bad part (or maybe good) is that you need the 
telescope finished first to figure the mirror.  You put the mirror in the 
cell, center a bright star and get out a high power eyepiece.  You then 
examine the diffraction rings while moving slightly inside and outside of 
focus.  An uncoated, polished mirror reflects sufficient light to do this on 
very bright stars.  Dick Suiter's book 'Star Testing Astronomical Telescopes' 
goes into great detail on interpreting the results. A synopsis of this book 
can be found in the March '95 issue of Sky & Telescope.  You analyze the 
figure, take the mirror out of the telescope, figure, test again etc.  This is
how it was often done a century or two ago.

Good Luck,

John A. Volk