Re: ATM Defining Super-Planetary

[andydtg@phoenix.net]

Bratislav writes:

>The "magic" of small long f/ratio reflector (and indeed a refractor, as
>most of them will be in a 6" class) is that tunes so well to local
>seeing conditions in an average amateur establishment. It is no
>surprise to find that Pickering himself, when defining his famous
>seeing scale said 'telescopes below 6" not recommended, above 6" not
>allowed' or something to that effect. But patience, and especially CCDs
>change that, and today practical "limit" is closer to 12" for most, and 
>up to 16-20" for best amateur sites.

You've just verified the results of a professional study done back in the 50's
(I think) in connection with visual monitoring of planets (mostly Mars/Jupiter)
which attempted to answer the questions: what aperture yields the 'best'
high resolution image most of the time (important for continuous data)
and what gives the 'best possible' image a small fraction of the time. The
results were 11" and 16" as I recall. My own experiece with a 9" off-axis
mask on
my 24" f4 and a 13" mask on the 32" confirm the 11" most of the time result, Don
Parker's 16" CCD images the other. I built a 10" f8 for a friend once with
a Gene Fair mirror & 2" diagonal that would show the spokes on Saturn's rings
on a good night.

My other input - a stationary image is virtually essential for high power
planetary viewing to catch the moments of good seeing, pushing & shoving
Dob style just won't hack it. Mel's drive system (and mine) allow this and
keeps the compactness, convenience, and stability of the alt-az mount.

I'm off to the Texas Star Party, hope to have met some of you there!





Andy Saulietis / DTG Alt-Az-Fp Drive Systems
HDPE Worm Gears, Custom designs & Machine work
12617 Harriet Ln
Santa Fe, TX 77510 USA
409-925-8854 Voice/Fax
e-mail: andydtg@phoenix.net