Re: [ATM] Astigmatism in round robin mirror C with Foucault.

[Michael Peck <mpeck1@ix.netcom.com>]

At 11:20 1/13/05, Douglas S Angle wrote:

>There's been a number of questions and comments on this list about the
>ability to measure astigmatism using foucault.  I think the consensus is
>that, since it can't be seen in the test, it can't be measured.  There
>have been some dissenting views on this, sometimes from the same people
>making the statement in the first place (myself inculded)!!!  See for
>example:  http://www.atmlist.net/pipermail/atm/2004-March/001124.html
>
>I was asking about the use of the fitted COC value to estimate
>astigmatism, and was told yes (and no), it can (can't) be done.

I don't want to speak for Jim, but I think he changed his mind about that 
over a period of 4 years. His 2004 opinion is the one you should listen to, 
although I'd change nanometer to micron.

One problem with both Sixtests and FigureXP is they crunch numbers 
(correctly) and come up with a reference surface RofC that they print out 
with considerably higher precision than the accuracy of the input data 
warrants. Try changing Sixtests' "X-bias" entry [I think that's what Jim 
calls it] by +- 3 or 4 mm. and see what happens.

Mike Peck



_________________

Michael Peck
email mpeck1@ix.netcom.com
Wildlife photography page http://home.netcom.com/~mpeck1/index.html
Amateur telescope making http://home.netcom.com/~mpeck1/astro/astro.html 

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