ATM RE: 12" refractor

[Roger Ceragioli <rogerc@dakotacom.net>]

Kevin,

Jokes aside, if you look in the March 1978 S&T you'll find an article about
Jeff Schroder who built an 11" portable refractor.  He used to transport it
in and on top of his car: the tube rode over the passenger compartment.
The instrument was, of course, enormous. 

The best way to shrink the tube and make the scope more portable is to
employ two folding flats in an "N" arrangement with the objective at the
top of the right vertical stalk of the "N", the first flat at its bottom,
and the second flat at the top of the left vertical stalk.  Tilt the
mirrors slightly to make the light go through.  This reduces the tube
length to 1/3 of normal.  And you still view from the bottom up.
Incidentally, these "flats" don't have to be very flat to work well.  They
can be curved by several waves and you won't detect the difference in the
image.

In this way, a 12" ft. tube can be reduced to 4"--much more manageable.
Still the scope will be heavy--maybe 100 lbs? because of the weight of the
glass (flint weighs several times as much as crown), the cell, the folding
flats, and the solid tube itself.  And you'll still need a stout mounting
and way of elevating the scope up to the equatorial head.

For a really first class scope, you will probably want to buy the glass
from Ohara or else from Schott directly.  Newport glass sells kits, but
Newport isn't necessarily reliable.

Personally, I suspect that a very well-made Cassegrain of f/25-30,
employing a small secondary, aluminum tube that's well ventilated, and
capped with an optical window will perform as well or better than your
proposed refractor.  It will also be cheaper, lighter, probably shorter,
and totally apochromatic.

Good luck, whatever you decide on!

Roger Ceragioli