Ron Oehlert said:
I'm 68 & have been viewing & making telescopes since 1956 & in the past I was a contributing member of the Association of Lunar & Planetary Observers(ALPO). There is simply no significant planetary detail visible with less than 6" aperture and 8" improves on what may be seen. True, long-focus large-aperture reflectors (most planetary bang for the buck) are no longer mass-market scopes, but they are still commercially available (Discovery for instance offers an 8" f/7 reflector & highy portable 6" f/8 reflectors (which trumps any 4" aperture refractor in capability & cost) are still available while an 8" f/6 is also a fine planetary instrument for not much more cost or portability sacrifice than a 6" f/8 reflector. Driven equatorial mounts or platforms are also necessary, because wide-angle eyepieces are not the best choice for viewing subtle planetary detail due to their many glass elements, nor is a moving target ideal; plus driven mounts permit comfortably waiting for those moments of good Seeing & while the target is centered. Cats are also not great planetary instruments owing to their large central obstruction at any aperture. Simple reflective optical systems & large aperture, long-focus is King for the planets plus is lowest cost of all. Atmospheric disturbances aside, what use is any view if no fine detail can ever be observed because of limited aperture? At age eleven I was impressed with the view thru a small refractor, but soon realized that all I could see was a crisp outline devoid of any surface detail beyond indistinct shadings; it takes much greater aperture to reveal low-contrast fine detail on planetary globes or within Saturn's rings or to show Jupiter's moons as more than points of light. A 6" f/8 reflector is minimum per instrument size in this regard while a Konig-type eyepiece & Barlow provides a wider field than an Ortho for good planetary performance even without a driven mount (That is bang for the buck & easily portable, too).
Ron, I noticed that this scope is on the market
PT 8" f/9 Planet Pro Dobsonian for about $1000.00. It has a 1.25" diagonal, but has a 2" focuser(?), which strikes me as odd. It does have a 3 vane curved spider.
