RE: [APML] Celestron vs. Meade

["Gene Horr" <genehorr@houston.rr.com>]

> [mailto:astro-photo-bounces@seds.org]On Behalf Of Dale Ireland

> Thanks, the newtonian recommendation is interesting. I didn't 
> know they were that much better for planets. 

One clarification - the longer f/ratio Newts.  F/6 or slower, preferably
f/8 or slower.

> Is this due to the smaller central obstruction and fewer glass surfaces?

Smaller CO, at around f/7 aberrations start becoming immaterial, and
the primary becomes an easier surface to manufacture to a high quality
figure.  

The main downside is the size and weight.  People use Cassegrains for 
planetary work for convienience.  It makes a small light package.

You could probably build one for about the same cost as a C-11 with
a carbon fibre tube.  If you are enthusiastic with baffling it would
perform noticeably better.  But if you do so don't make the mistake
that most ATMs do of going for an inexpensive flat.  That surface
from the optical quality standpoint is actually more important than
the primary!  (The same thing applies to visual diagonals, but that's
another OT thread...).  A high quality flat is not a trivial surface
to make.

> The problem is that I would like to avoid having to buy a new pier for 
> the 900 (or a big stepladder).

Well, nothing's perfect <g>.  But a 4' ladder for standing or 5' for
sitting might work and would still fit in the back of a small car.

Gene Horr
genehorr@texas.net


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