Re: [APML]: newts

[Michael Stecker <mstecker@earthlink.net>]

I agree with Chuck's comments.  You obviously can't say all
Newtonians have a flexure problem unless you have used them all. 
However, I must admit that I have never seen a first rate
astrophotographer with a standard Newtonian larger than 7 inches use
anything but an off-axis guider.  I have used my Takahashi 8-inch f/4
"Newtonian" (Epsilon 200) with a guiding refractor for many years and do
get significant flexure for exposures longer than 45 minutes.  Shorter
exposures however, are acceptable.  In 1996 I spent 10 nights at the
Carnegie Southern Observatory at Las Campanas, Chile.  The telescopes
they used ranged from 24-inch to 100-inch. They were all used with CCD's
which require shorter exposures than film.  None of these research grade
telescopes used a guide telescope.  I was also told by a Palomar
employee that the famous 48 inch Schmidt camera does suffer from flexure
when used with their guide scope. This has limited the exposure time for
this instrument.

                        Michael Stecker