Re: ATM chipped mirror

[Andy Saulietis <iss@pvtnetworks.net>]

Mel Writes,

>Simply put the edge restrait clip over the chipped portion of the
>glass.  That way it will not be a problem cosmetically when you show it
>off.

I did the same with my old 24" which had a 1/2" edge chip. You
can minimize diffraction from the clips by using circular
clips spaced so the parts of the clip (short arcs) inside the mirror's
edge add up to 180 or 360 deg relative to the diameter clips (ie for
3 clips each one would be 120 deg with the clips also spaced
120 deg apart, or 90 deg for 4 clips etc). This is the same
technique used for curved secondaty vanes. Placing the clips
in the shadow of the secondary vanes also helps.

The McDonald Obs 107" which suffered an attack by a deranged observatory
assistant some years ago, in which he emptied a pistol at the primary
mirror, causing several ~1" dia craters on the surface, was 'fixed' by 
covering them with ~2" dia black masks, thus reducing the diffraction
at negligible loss of area.


Andy Saulietis
ISS Enterprises
39 Silver Fox Trail
Mayhill NM 88339
505-687-3067 voice
505-687-3021 fax, call voice or e-mail to set up
e-mail: iss@pvtnetworks.net