From: "Good, Donald" 
To: ATM Archives 
Reply-To: "Good, Donald" 


The size of the cHip does not affect the flatness of the mirror, but can
cause interference effects in the image.  This depends in part on size,
shape, location, the size of the fully illuminated field of view, and
illumination at the edge of the field (assuming the chip is at the edge).
In general, if the size adds less than 1 or 2% obstruction, especially at
the edge, it will not be noticable in most seeing conditions.  Paint the
chip area a flat black to prevent stray reflections and try it out.

-----Original Message-----
From: Daniel Fundo [mailto:fundo{at}bellsouth.net]
Sent: Sunday, March 23, 2003 1:07 AM To: Chuck Taylor
Cc: ATM Archives
Subject: Re: ATM chip on diagonal



<< Assuming a good quality to begin with (it is a Televue) how big a
chip would you estimate you could have on the mirror of a refractor style
diagonal before it would affect the flatness of the mirror?  >>

It doesn't matter how big the clip is!  It's how its placed on the holder
that will affect flatness.  If the clip isn't designed correctly (to just
clear the thickness of the mirror) then any over tightening will induce
strain on the mirror.  Generally, a thin peice of felt is attached to the
part of the clip that is over the surface to avoid scratching.  A slight
compression of the felt will not affect the mirror, unless it is very thin.

Several of us on the list still believe in mechanical attachment of all
mirrors to their cells/holders, but for a secondary, especially a small
one, I believe that silicone adhesive, in moderation, is acceptable.

*****-----
Dan F.
Secretary/MAS
Memphis, TN

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