Re: [ATM] Time for a "new standard" ATM telescope project?

[David Weinshenker <daze39@earthlink.net>]

"Eric S. Johansson" wrote:
> How can you build a 10 inch f15 that can be used
> without climbing to the top of a ladder?

High-secondary-ratio "bent-Cassegrain" system, perhaps? 
A small diagonal mirror near the primary could send
the light from the secondary to an eyepiece located 
conveniently on the side of the instrument, and the 
shorter mechanical length would improve the rigidity 
of the alignment.

With increased secondary ratio, a smaller secondary is needed 
(less obstruction) and the ideal "hyperbolic" surface approaches 
a pure sphere (easier to figure) - for example, T.R. Endemann 
(S+T, Nov 1998, p.121-126) describes an 8-in. f/70 "Planetary 
Astrographic Telescope" with an f/4 primary, and notes that it 
works quite well with a spherical secondary mirror (which he 
calculates to be within 1/10 wave of the "optimum" hyperbolic 
curve for the 17.5:1 secondary ratio).

I discovered Endemann's article while researching the "more 
complex idea" that I mentioned in my other message, which is 
along somewhat similar lines, except that I was thinking about
the possibility of replacing the convex secondary mirror of the 
traditional "Cassegrain" layout with a combination of a plane 
mirror and a concave lens... preliminary calculations indicate 
some interesting characteristics, such as a potential for rather 
high - and highly adjustable - magnification. (I could post my 
notes so far if there's interest.)

Another alternative: mount a CCD camera at the prime focus, 
and view electronically from ground level: there's some awfully 
compact industrial Firewire cameras out there... I've got a 
brochure on the AVT "Guppy" models, which are 48mm long and 
30x30mm square in cross section: the C-mount (1in x 32 TPI) 
port basically takes up the front of the camera body; the whole 
camera wouldn't be a very severe central obstruction for a 10 
inch telescope!

-dave w
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