Re: ATM Defining Super-Planetary

[Bratislav Curcic <epabcc@epa.ericsson.se>]

> super-planetary scope

Do you want to use it visually or photographically/CCD ?

If _recording_ is your goal, then large aperture, good optics and
patience (waiting for moments of good seeing) is a ticket. There is
really no advantage to any particular optical system over another in
this case. See "High resolution astrophotography" by Dragesco where
people have taken some absolutely incredible images of the Moon using
Celestron 8 (most people will never SEE as much detail as these guys
photographed!). Dragesco himself used C14 a lot, and more or less all
other examples have been obstructed scopes (with exception of one 8"
refractor and couple Schiefspieglers). But MOST photos in the book have
been taken with plain ol' Newtonian, so that would obviously be the 
choice for serious planetary observer/recorder. Dragesco himself favored
a well figured 10" Newtonian over all other scopes he had (and he
owned 32 of them, including 7" Astro Physics and 10" Takahashi).

If _aesthetics_ of the image is your goal, then you'll have to go
unobstructed. Of all unobstructed systems, off axis mask in a large
Newtonian is the simplest (and cheapest!) way to do it. Next step is
dedicated unobstructed system : tilted scope a ka Schiefspiegler or
Yolo, purposefuly built off axis scope like off axis parabola or off
axis Maksutov, or refractor/Schuppman. If you want best visually
performing telescope for a given aperture, you'll have to shed big
bucks for glass needed to make an APO. Very close second will probably
be a Schuppman (chiefly because of scatter introduced by relaying
mirror). Also close runner ups will be an off axis Maksutov and a
traditional long focus achromat (all these have advantage of closed
tube). Tilted systems do promise a lot, but do suffer from tube currents,
especially in larger specimens.

Just as a side note; the recent popularity of APOs have to do with
two things (in my opinion) : 
1. most people are just too impatient to wait for that rare moment 
   of good seeing to convince themselves that say good 12" Newtonian 
   is indeed much better planetary scope than a say 6" APO;
2. most amateur observing sites rarely do offer seeing good enough for 
   a large scope to exploit it's advantage "full time"; it boils down
   to (1)

To get one exceptional image worth an entry in the above book for
example you may have to wait for YEARS and shoot thousands of images.
If you look in the log book of a serious planetary buff, you will se
that one imaging session usually lasts for several hours and results in
several HUNDREDS of images.
The "super-planetary performance" doesn't come from the scope alone, 
it is the _observer_ who uses it that makes it perform. Maybe that's 
why Don's and Isao's images come so close to what people with much
larger scopes and at much better places do.

Bratislav