RE: [ATM] Too Small Optics-( and flex produced optics)

[mdholm@telerama.com]

Jerry wrote:

>I don't buy into the super smooth argument for bending and figuring. Nor for
>that matter figuring and bending. What means of ACCURATELY bending a glass
>disk into some conic so that the sphere can be installed on the surface so
>that it can be released into that superior conic.
>
>Now, I'm sure there are many amateur machinists who will be able to make
>that edge support accurate to a half a millionth of an inch. But now that we
>are "flexing for figuring" we have to move that support to the front of the
>mirror and push that patented plunger into the back of the mirror to force
>it to the proper negative of the positive, or is it the proper positive of
>the negative conic we want. And maybe we need to be accurate to a half a
>millionth inch on this also. Gee I hope errors don't add up. And I hope that
>flexing machinery doesn't get in the way of the lap.

You need to read Bill Kelly and Alan Alder's Sky & Telescope articles:

This is one of them: I am having trouble locating the other.

Flexing Spheres into High-Quality Telescope Mirror, November 2000,  p. 131-140
(purchase .pdf file at
http://skyandtelescope.com/shopatsky/_additem.asp?aaid=200011131140 )

The short answer is that millionth of an inch machining accuracy is not needed
if you play the material properties game correctly.  There are some precision
requirements that are not usually required for mirrors, but they are not
terribly difficult.

Mark Holm

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