RE: Re ATM Barlow, Focal extender...

["Anderson, Jay" <andeja@mail.va.gov>]

Considering building a telescope optimized for visual observing or
astrophotography represents a problem.  I have found Protostar
(http://www.fpi-protostart.com) makes a wonderful diagonal mount that
can be made to switch out an extra diagonal holder if you want to have
as small a diagonal as possible for visual observing and a larger one
for astrophotography.  Ask for a catalog at protostar@fpi-protostar.com.
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From: Nils Olof Carlin
To: Jack Schmidling
Cc: atm@shore.net
Subject: Re  ATM Barlow, Focal extender...
Date: Thursday, May 08, 1997 6:27AM


Jack,

I haven't tried astrophoto with a full-size telescope but on general
principles, the requirements for best photo and visual performance are a
bit too far from each other.

You have been discussing your 16" on the list, but I am not sure if you
have the Sonotube or have switched to truss tube (I believe you have
considered this). In the latter case, I think that making one diagonal
cage
for photo only, and another for visual only (with smaller diagonal and
low
focuser, and a little longer to reach focus), would likely work as
smoothly
as possible with the mechanics optimized for each use.
It would mean, of course, that it would not be quick and easy switching
between photo and visual but maybe if you have a common plywood ring on
the
truss tubes, you could make some reasonably quick fit for the diagonal
cages (fine collimating would be de rigueur for visual, but not quite
for
photo I believe).

The Barlow would increase the focal ratio, I see no practical way round
this.

Nils Olof