Re: ATM Calculation of Prime Focus.

["Tom Mchugh" <tbmchugh@ainop.com>]

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> 
> At 02:49 PM 9/14/97 -0700, you wrote:
>
> in fact, I have never heard of an amateur taking a picture at actual
> prime focus. (Though I guess I am about to if they did.)

Jeff,

You left yourself wide open on this. Clarence P. Custer. of Stockton,
Calif. built a massive 12.5 inch f/8 reflector, a combination visual
instrument, using the Springfield focus, and a photographic instrument
using a prime focus camera taking 2 X 2 glass plates (cut down from
larger 103a-0 glass plates).  This telescope was completed circa
1955, and featured in an issue of S & T in 1957, along with several
of his photographs--incl;uding a superlative three image montage of
M-31, M-32 and NGC 205.

One of the features of his camera is that it had plateholder guiding, 
which allowed for precise image tracking, even if the image movement
was caused by tube flexure, or any inaccuracy in his polar drive rate.

I no longer have my early back issues of Sky & Telescope, but I am
sure that you could find references to the Custer telescope in the 
S & T Index (I think it may have been June of '57).

Hope this helps.

Tom McHugh