From: "Bob May" 
To: "atmlist" 
Reply-To: "Bob May" 


I've still got Richard Schwartz's mirror as he hasn't picked it up.  The
glass is double thickness (1/4" thick)  front, back and ribs. There's
a picture of it at:
http://bobmay.astronomy.net/mirrormaking/mkfoucault.htm
down near the bottom on my mirror stand.  Yep, that is a geared motor under
the mirror, as well as another one behind the mirror, to control the
pointing of the mirror from the tester end of the setup. The mirror is the
last of 8 mirrors that Richard made, this being the only one that hasn't
been broken in the process of grinding and polishing.  The ROC is 85"
and that mirror has a 1/11th wave surface on it with the biggest error
being the slight rollof of the edge zone. The biggest problem that I had
with the mirror testing is that all of the surfaces are near that ROC so I
get multiple reflections from various parts of the other surfaces.  There
is one area of about 2 triangles that seems to have exactly the same ROC as
the front surface but a slightly different angle so that they stay bright
while the rest of the mirror is dark.  That had to be put towards the top
or bottom of the mirror so that the rest could be tested.
Four hours were spent at 320 grit to get rid of a little dimple in the
surface as cast followed by about 8 hours polishing and then 4 hours
getting a sphere and another hour figuring.  The work after getting the
glass polished was all done with rouge as the CeO was making the surface
dogbuscuity rather badly.
AFIK, the glass is ordinary plate glass and it worked like that. One
interesting comment from those that saw the mirror at RTMC was
"Why?" as most larger telescopes use the weight of the glass in
the cell as the counterbalance to the top part of the scope and some weigt
is needed down there.
Supposedly, Richard is working on some larger mirrors and I've asked for
one to be setup for a Cassegrain design for myself. Bob May
http://nav.to/bobmay
bobmay{at}nethere.com
NEW! http://bobmay.astronomy.net

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