RE: [ATM] 25" mirror possibilities (Chapter 2)

["Cary Chleborad" <Cary@Chleborads.com>]

> Case 3:
>  The alternative to a folded Newtonian seems to be to actually regrind the
> mirror to a shorter focal length, say f4 at a much higher cost and more
> coma.  For an f4, a conventional 5" diagonal 16" from the focal plane
> would give a similar size illuminated field with a 20% central
> obstruction, and a required ladder height of about 2 feet.

Given the importance of the thermal mass issues, re working the material
into something else would really be the best bet.  If this mirror were to be
treated as raw material, you could have it slit into two blanks provided it
is thick enough.  You'd then en up with two "normal" thickness (in modern
terms) blanks. 

Better yet, you could have it slit into three or four thicknesses and have
Jean-Guy Moreau fuse it into a post and beam type cellular structure.

Some would think it a sacrilege to destroy a Tinsley optic, but it's just
glass.  We know a lot more about the properties of the materials we work
with today than we knew 30 years ago.  Make the best of the material.


-Cary


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