RE: [ATM] refiguring a 20 inch Pyrex f/2 cassegrain

["Thomas Janstrom" <tomjan@ozemail.com.au>]

Hi Guy,

If optimised for IR work the wavelength of light used to do the figuring
could have been in the far red (say 700ish plus nm), and so although it
might have been 1/20 wave at that WL if you now test at say 550nm it
won't be any where near that good, in fact (although I haven't done the
maths on this yet) it might even be less than 1/4 wave, which is why it
appears not to have been figured very well.

Cheers, Thomas

-----Original Message-----
From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net] On Behalf
Of Guy Brandenburg
Sent: Monday, 8 August 2005 8:18 AM
To: atm@atmlist.net
Subject: [ATM] refiguring a 20 inch Pyrex f/2 cassegrain


Has anybody ever tried refiguring a 20 inch Pyrex f/2
(or thereabouts) Cassegrain? I understand that the
primary on the one I have in mind - it belongs to the
Hopewell Observatory, of which I am a member - is
supposed to be parabolic, and that it's not figured
very well. Supposedly it was optimized for infrared wavelengths, but
that doesn't make a lot of sense to me, because reflective optics
reflect all wavelengths the same way.

I am considering refiguring it, but I've never worked
on anything either that large or that fast. (I am
working on a 16.5" parabolic f/5 pyrex primary, but
have not yet gotten to the polishing stage, much less
the figuring stage.)

Any comments from anybody who has actually done that
would be more than welcome.

Guy


Guy  Brandenburg
Washington, DC
My home page: http://home.earthlink.net/~gfbranden/GFB_Home_Page.html
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