RE: [ATM] Optical flats

["Julio Sanchez" <jsanchez@skipanon.com>]

Thanks Bob. I am fascinated by the art of making optical flats. Some years
ago I started making a 10" Ritchie Chretien telescope and spent the better
part of a year making flats. At that time I ended up with one good one
(about 1/10 lambda) and two not so good ones, one of which I gave away and
the other one became my "master flat". My good one, which has a 2 3/4" hole,
sits in a cradle that is part of my autocollimation rig. The silver coating
is now pretty tarnished, so I will have to re-silver it or send it out for
aluminizing.

Is it really possible to sell a flat on ebay? Even one made of plate glass?
For how much?

Thanks, and regards,

Julio

-----Original Message-----
From: Bob May [mailto:bobmay@nethere.com]
Sent: Wednesday, January 05, 2005 6:57 PM
To: Julio Sanchez
Subject: Re: [ATM] RE: Stabilizing plate glass

Don't consider the flats to be good for testing other flats and you will not
be sorry.  Making a flat for autocollimation means that once you set up the
tester, you don't touch the flat and it will hold a good figure.  Also, a
flat sitting in the bottom of a light fixture won't be touched so it again
will tend to be quite stable and thus good for testing.
I'll agree with the others that plate glass isn't the best for making flats
but the stuff will work if you understand where the limits are.  Besides, do
a set with plate glass and you will understand the problems of making flats
and you can also sell the flats if desired on eBay as soda lime glass
(another name for plate glass) flats and get the money to make some bigger
ones with pyrex.
Bob May
bobmay@nethere.com
http://nav.to/bobmay
http://bobmay.astronomy.net

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