Re: [ATM] 8 inch gregorian mirror

[David Weinshenker <daze39@earthlink.net>]

Wayne Hilliard wrote:
> 
> Gentleman,
>       Its been a while since Ive posted here all though I do read it
> periodically. I have a question, I'm figuring and 8 inch mirror for a
> Gregorian I'm building. I went ahead and removed the core from the center of
> the mirror. It polished out fine with a full size lap that I trimmed the
> center facets out of. I'm debating what the best way to figure this is.
> Regular figuring stroke or some other combination there of. Ill be
> interested to see your comments. I do realize that I should have left the
> core in but that's water over the dam so to speak.

I'm not sure what the issues are with figuring an apertured 
primary; if that's what you're asking... One set of answers 
I've seen is to somehow glue or plaster the core back in
temporarily and then remove it once the mirror is figured.

However, it occurs to me that one advantage of the Gregorian is 
that the concave ellipsoidal secondary should be straightforward 
to test, at least: a pinhole source at the near focus should give 
a flat null against a knife-edge across the far focus.

-dave w
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