From: "CSC" 
To: "Atm" 
Reply-To: "CSC" 


some glass, especially the more desirable ones required in a large well
corrected doublet, would run 20k.
When you get up into big refractors, the scope will cost a lot and a good
lens is essential.
20-30k for a fine 11" is reasonable. I guess.

Colin

-----Original Message-----
From: owner-atm{at}shore.net [mailto:owner-atm{at}shore.net]On Behalf Of Bob
Walker
Sent: Friday, June 27, 2003 1:27 AM To: ATM Group
Subject: ATM Large refractors



Here's a question for you wizards:  How about making a large refractor out
of plastic?  One of the stumbling blocks to making refractors is the
astronomical (sorry) cost of large pieces of optical glass.  What about
using optical plastic of the types used for  making eyeglasses?  Is it
available in liquid form like the familiar polyester resin/hardener
combination used with fiberglass?  If so, a large lens blank could be cast
easily.  Could it be ground and polished by the same methods/materials used
on glass?  (Much more quickly, one would think!)  Another barrier to large
lenses is that they sag under their own weight.  Plastic is much lighter
than glass, though also less stiff.  Would its stiffness/weight ratio be
better or worse than glass?   Are said optical plastics available with
suitable refraction / dispersion characteristics to allow design of an
achromat?  What got me thinking about all this was reading about an
11" refractor being made by amateurs the glass for which cost $20,000!
 Less than some of us spend for a car, but still prohibitive for most. 
Think of it - the largest refractor in the WORLD is one lousy meter.  Some
ATMs have made mirrors bigger than that.  What a coup if one could make a
bigger refractor!

 *  Best regards, Bob
*
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