Hi Wavytone & All,
Quote:
Originally Posted by Wavytone
Dobs are far from optimal for planetary visual observing ... secondary too big, not enough focal length, the SW mounts are too stiff, and at high power tracking is not easy especially with a stiff mount.
Long focal length (and f/ratio) is required... get a 150 or 180mm mak or 200mm SCT on a GOTO mount - though either will cost more than the dob.
A 150mm mak on a SW All-View mount would do quite nicely on a modest budget, and would eat the 100mm refractor on anything.
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Must say I have to disagree with much of your post. Of the commercially available Schmidt-Cassegrainian telescopes, all have central obstructions in the order of 36-40% and are inherently low-contrast telescopes **when used visually**. Maksotovs generally are better on this front but aren't in the same league as a good Newtonain. Yes, most of the current crop of off-the-shelf Dobson-mounted Newtonians do have what I consider to be over-sized secondary mirrors and are about 25% obstructed, but a much better in that department than all the commercially available S/C and Maks.
A Newtonian optimised for visual work (about 15-20% obstructed) assuming good-quality, well collimated optics are superb planetary performers -- second only to a fine refractor inch-for-inch.
I do share your view on some of the dob-mounts that re not particularly pleasant to use, but they can be tweaked very easily and cheaply to make them adequate performers.
There is an old adage (that so many these days forget): Visually, a good big telescope will beat a good little telescope any day of the week both in light-gathering power and in resolving fine detail.
Recently I had a friend do "first light" on his second-hand Takahashi 150mm f/9 refractor (a gold-standard 6" telescope if ever there was one) side by side with my 18" Newtonian. The Tak cost nearly $10,000 second hand (and that's just the tube) and my 18" cost me about $7,000 including the mount and all the bells and whistles like digital setting circles and servo-cat drive. Guess what? My well-made 18" f/4.9 with a 17% secondary mirror flogged it to death on Jupiter. The image is nine times brighter and three times better resolved (in perfect conditions). In the Tak, the Jovian moons were beautiful little star-like points. IN my Newtonain Ganymede & Callisto were tiny little *globes*. When we looked at just a few deep-sky objects (and were talking bright eye-candy objects), the Tak was a very long way behind.
Yes, *visually* a good big telescope will beat a good little telescope -- every day, in every way.
Best,
L.