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by Dave North
Art:
I noted the comment about dobs limiting one to low powers. I use an 18" F4.9 dob routinely at powers of 250X and above.
We had one of those nights last night, and insomnia kept me up late enough to see Jupiter get way up there. Very solid at 300x through the C8 and I was able to get a good look at the GRS and the trailing ovals everyone's been talking about.
A couple of weeks ago someone asked me what's up; that it looked like the SEB was "gone" behind the red spot, and while the planet was still low, it looked that way. When it was a bit higher and the spot had rotated a little past the meridian, I finally made out what was going on. Weird illusion when I first looked -- like the SEB had disappeared (along with the GRS). But later I could definitely see the color in the GRS also, but it looked like the GRS Hollow had not much more than half filled in. I'm sure most of you had already seen this, but I haven't been able to get much Jupiting in yet this year.
Great transit last night. Got to see Ganymede's shadow very distinctly, followed (around 12:30 local PDT) by the moon working its way across the south polar region, where limb darkening made it stand out very distinctly. Curiously, in that setting, it was very easy to see the disk of the moon (but, alas, I could glean no detail for sure).
Tried up to 500x on Saturn, but it wasn't much better than 400x and definitely didn't look as "nice" that cranked, so I stayed mostly at 400. At both mags, the enkeeler smudgygap was very distinct, and the rings had a much more complex look than usual, though it really boiled down to just the usual A/smudge/A/Cassinigap/B/Crepe combination -- maybe just a little more distinct than usual.
Nice look at the Moon, too, especially the central rille complexes.
Oh, the point: I found myself very much wishing I had rolled out the 12.5 to cool off, since it seemed like the kind of hot, still night where it could have actually earned its keep in the shallow sky -- sometimes the extra aperture does pay off.
But, of course, it's a dob. And I've run it at 400x fairly often. At that mag I can only look about half the time (fairly constant shifting) but it's not a huge debility since the on/off/on style of viewing suits me okay. Rests the eyes so I can go for a longer overall time slice. Very hard to draw like that though.
And, lest anyone have any doubts, I really do far prefer driven german mounts to everything else; it's just that I can still dodder by without one, and really don't think they're an absolute must. What is critical is tuning a dob's action: some are so shaky or jerky that you really can't get over 200x, where one that works "just right" is not outrageous even as high as 600x (though that's a real horse race).
As a final comment, I am more and more convinced that a top-quality ten-inch semi-long focus newt (around f/6) on an eq platform may be the best performance/dollar/peak investment overall for a planetary nut who gets reasonably good seeing on a regular basis.
But I ramble...