From: "CSC" 
To: "Atm" 
Reply-To: "CSC" 


FWIW
The artificial star needs to be some 20 times the focal length so you don't
see undercorrected star patterns.

I like the thicker mirrors, myself.

Making a sphere gets rid of all quantitative analysis.  There's no doubt
about a true null.  If the Foucault makes defects visible in the range of
1/40-1/100 wave, why not take advantage of this elegant test.

Colin

-----Original Message-----
From: Harold [mailto:adams{at}rmci.net]
Sent: Wednesday, February 12, 2003 12:45 PM To: CSC
Subject: Re: ATM flex mirror spring tension ?





 What could go boing>
 > Wind it up.  >

  Colin, Bill and all. Thanks to your information i shall procede with
confidence. But if this thing exploads...  : 0 )

   Francis,thanks for you suggestion, but the artifical star is not close,
it's a convienient christmas tree light on a hilltop 3 1/2 miles distant.
Now that i think about it, in the past i have used artificial star tests on
other scopes and at varrying distances and although i have since heard
evidence to the contrary, i have not been able to detect much difference in
the tests weither close or distant. Im am not that experienced an observer
and am not suggesting that there is no difference. Just sharing my limited
experience.

   Russel, your suggestion of thinner glass has it's merrit and innitally i
considered a thinner glass but the flex program indicates that a 1
1/2" thick x 12.5"  f /6.68  mirror will work, and at least in
theory is capable of flexing to a better figure than a like size but
thinner mirror. I could be wrong but i think the thicker mirror is also in
less jeaporady of flex induced astigmatism than the thinner glass but even
at that im not sure the advantages of thicker outweigh the disadvantages.
Im not done testing the scope yet and your idea of thinner glass may prove
to have been the better way to go.

   Richard, Richard, Richard. You have my word, i won't say anything to
Mr.Adler about your idea although i think you make a good point about
starting out with a 50 figure :0)  Come to think of it i believe i also
read similar comments mentioned elsewhere.

  Harold

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