Re: [APML]: AP600 v. 900 for C11

[Wil Milan <wmilan@airdigital.com>]

Bob Fera wrote:

> I, like many other astrophotographers, am of the opinion that you can't have too much 
>mount -- my C-11 sits on a AP 1200. Given that, I'd definitely recommend the 900 over 
>the 600. I previously owned a G-11 and felt that it was inadequate for shooting with a 
>C-11 (fine for visual, though). The slightest amount of wind was enough to give it  and 
>the autoguider fits.

I don't shoot when gale-force winds are blowing :-), but under more normal conditions 
I've experienced no such problems with a C11 on a G-11 mount.

I *have* had the experience of high winds playing havoc with guiding even though the 
winds were *not* blowing on the mount. In that case the guide-star jitters were due to 
the wind howling over the hill behind me (the "hill" was actually the top of a mountain 
ridge; I was located just below the top). The extreme turbulence caused by the wind 
cresting over the peak
above caused jittery guide stars and erratic guiding, looking very much like mount 
vibration, but in fact the mount was in still air. (That was an AP mount with an smaller 
scope, but it wouldn't have mattered if it was Palomar 200" mount; the motion was due to 
the air moving, not the mount.)

As a practical matter I've found that when strong winds are blowing the seeing will be so 
poor that it's not worth bothering with narrow-angle photography. Even when wind on the 
mount is not a factor (as above), the star images will balloon to the point that the 
photo will never be outstanding.

Wil M.
--
"When I consider your heavens, the work of your fingers,
the moon and the stars which You have set in place,
what is Man that you are mindful of him,
or the son of Man that you care for him?"  -- Psalm 8