Re: ATM 3 blobs enough?

["Tom & Lou Krajci" <krajcit@3lefties.com>]

From: Jeff <jeffr@phonetech.com>

>For a 10" diameter, 1" thick mirror, are three blobs of silicon adhesive on
>a plywood mounting disk sufficient, or should I construct a 4, 6 or 9 point
>mirror cell?

My ten inch mirror is 1.3 inches thick.  Richard Schwartz's analysis of this
thickness glass had him recommending a four point support.  Your thinner
mirror will need at least four, and perhaps 6 points.  If you download David
Lewis' PLOP software you can run analysis for a six point support easily and
see what peak and RMS distortion the mirror cell will give you.

Another thing to keep in mind...don't forget some ventilation holes in your
plywood disk mirror cell.  Also, don't make the RTV pads too thin, or there
won't be enough room between mirror back and cell to allow enough air
movement for good ventilation.  I strongly recommend a fan supported on
rubber tubing behind the mirror to further improve cool down speed, and even
to be used while observing.

Tom Krajci