From: "Mel Bartels" 
Cc: "ATM shore" 
Reply-To: "Mel Bartels" 


Doing a 12 inch for your first mirror in a class setting is challenging.  I
did a class at the Bellingham Washington Telescope Optics Workshop where
six experienced amateurs started with polished 16 inch blanks by Zambuto
making it through most of figuring by the end of the weekend (it was a 2.5
day class).

The idea always in classes like Dobson's and like mine is to learn
technique.  Never count on grinding a single mirror.  First of all, mirror
grinding is a learned art and your subsequent mirrors will always be
better, and finally, there is a lot of joy to be found in the artistry of
making any mirror.

To get a usable mirror and scope out of a class like Dobson's is a worthy
and only goal that should be considered.  Perfection comes elsewhere.

If the mirror in question has a turned edge for its main technique, then I
consider that quite successful for a first time effort.  Even experienced
amateurs have trouble with persistent turned edges.  Later, after using the
scope and getting all the enjoyment out of it that you can muster, and
becoming a worthy enough observer so that the turned edge begins to limit
you, you can go back and refigure the mirror to conquer the turned edge.
Often this is a few years down the road when the coating begins to fail and
needs to be removed anyhow.

Every mirror teacher, every mirror making book that I've ever come across
or read, including some unpublished books of which I have a copy of the
manuscript, have been very worthwhile and worth my time to revisit over and
over again.

Mel Bartels

--- BBBS/NT v4.00 MP