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

[Ric Rokosz <radicell2@yahoo.com>]

--- Guy Brandenburg <gfbrandenburg@yahoo.com> wrote:

> Has anybody ever tried refiguring a 20 inch Pyrex
> f/2
> (or thereabouts) Cassegrain? 

> 
> 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.)

You've been on the list for a while so you probably
have some idea of what's involved and the resources of
the archives and the tests that can be used.
MY vote goes for a null setup as it gives a clean
surface profile.You might consider the holographic
mask null setup that was presented a couple of months
back that would work without making any  additional
optical surfaces.
Going from a 16 incher to 20 isn't that difficult.You
do need smaller tools than what you've used before but
it's pretty easy to get the hang of things.Tricky to
be sure but not impossible.

Ric



		
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