From: "Bill T." 
To: atm{at}shore.net
Reply-To: "Bill T." 


>Richard Schwartz wrote:

>So, does your foucault tester have a knife edge, ronchi grating, or wire to
>cut into the focal point?    If the star test is so great, why don't you
>just get rid of your knife edge and use an eyepiece?
>
>I think that star testing can be useful... if you trash the eyepiece and
>replace it with a razor blade, ronchi grating, or fine wire.  35mm film
>cans
>fit perfectly into 1.25" focusers; cut a hole in the top and bottom of a
>film can and...
>

Yes, let's not forget that a star viewed with a knife edge at the focal
point is another excellent null test, the famous Foucault-Gram.  See the
illustration of the 82" 'Gram in Texereau. If only it didn't  require
a precision guidance system...

Has anybody had any success with Foucault-Grams using an artificial star?

Bill T.


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