Re: ATM Tex wanted an INSULATED tube!

[Adam Smith <ajusmith@xport.on.ca>]

Henry E. Paul did a nice argument on newtoninans optimized for planetary use
in "Telescopes for Stargazing" (1965, Amphoto). He called for sizing the
secondary only just large enough to eliminate vignetting, and the use of
window support for the secondary. The scope he depicts has a <vented> mount
for the window. He says the effect of sealed tube is very negative, but the
thoroughly vented window is useful.

The mount looks like a cell with a wide ring, most of which is cut away to
form circumferential slots. There are about 7 remaining points of contact
between the outer ring and the actual support, each about 1/8" thick.

I know there has been a lot of discussion about not going overboard when it
comes to minimizing the size of the secondary. Paul makes it clear that the
sizing should be done in regard to the intended use, and should not be taken
to extremes.

For what its worth.

Adam Smith