[ATM] Inverse Ronchi program

["eheiny" <eheiny@yahoo.com>]

I may need to evaluate the figure of a 21" f4.2 mirror.  The telescope
(Newtonian / Classical Cass) has been removed from service and put into
storage.  I've never looked through the telescope, but some that have
questioned the optical quality, while others say the mirror is OK but
suffered from thermal effects (thickness is at least 4").  Our club may be
able to get the primary mirror, but I'm hesitant to start a major project
without confidence in the mirror quality.  

While I'm comfortable using the Foucault test with smaller slower mirrors, I
doubt my skills at accurately analyzing a mirror this large and fast with
the Foucault test.  Hence my question about the inverse Ronchi test.  In
trying to research this subject, most search hits were dead links to
atmsite.org.  I have several questions:
Would the inverse ronchi test be a good test to evaluate the mirror?
How sensitive is it, i.e. does it have the sensitivity to detect small
errors?
If so, where can I find a link to a program to generate the inverse grating?
Any suggestions on how to print the inverse grating?
Should I also test for astigmatism?  Stress?  Methods?
Are there other simple tests I should try?

Hopefully someone can provide suggestions or links.  Thanks.

On a totally unrelated note, are there ways to cut a 23" dia X 4" thick
blank (Schott borosilicate glass) into two 23" blanks ~2" thick?  Are there
glass fab shops that could do it?  Would the cost be prohibitive?  Is there
a high risk of breakage?

Ed 
Louisville, KY
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