Re: [ATM] Refiguring cass mirror to newt

["Thomas Janstrom" <thomas@moiler.com>]

I've had to do this twice now; I make a pitch lap and carve out the centre
section to match (slightly over size) the perforation. This way you can
press as you normally would and work with the same strokes etc. you will
still get a slight turned edge around the perforation, but as this is
usually baffled by the secondary mirror it won't have any real effect on the
system's optical performance.

Thomas.

-----Original Message-----
From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net] On Behalf Of
Gord Tulloch
Sent: Monday, 30 July 2007 7:45 AM
To: atm@atmlist.net
Subject: [ATM] Refiguring cass mirror to newt

Hey all:

A friend has an (apparently) spherical 12" pyrex mirror, likely part of a
unfinished SCT. He wants to get it refigured to a paraboloid to use as a
newt - f4.8 so not too bad (haven't tested it yet) but usually I understand
when people polish and figure perforated mirrors they keep the core and
stick it in the hole with pitch. Any guidance on what I might do with this
mirror where we don't have a core? Don't worry about it, or fill it with
something else (dental stone?) so it doesn't mess up the lap? Thoughts would
be appreciated, thanks!

Regards,
  Gord
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