Re: ATM Optical Windows as Secondary Supports

["Bob May" <bobmay@nethere.com>]

Anything that you look through or get reflections off of has an effect on
the optics.  Even the air you look through does this (tube currents
anyone?).  Plate glass is good enough to look through with the naked eye but
when it comes to using it in a telescope, you need to make it to where it
doesn't introduce refraction (from changes in the glass refractive index,
thickness changes, etc.) problems of it's own.  Just not nice to have a good
mirror and hang a piece of glass in front of it that changes the flat
wavefront of the incoming starlight to something quite strange.  A Schmidt
Corrector Plate is a very special shape of the glass that makes changes to
the wavefront and the change in shape is on the order of flatness of a
ordinary plate glass surface from the glass factory.
Bob May
My new web space address is http://webu.wigloo.com/bobmay/ or
http://nav.to/bobmay
and my new email address is bobmay@nethere.com
Bob May