Selecting the Perfect Telescope

$Over on the SkyNews magazine Forum the question came up — “What’s the perfect telescope?” Bound to prompt reaction, right? OK — If I were forced to part with all but one telescope right now, I think I would elect to keep the TMB 92mm apo I reviewed recently in the March 2009 Sky and Telescope. I love small apos, and the TMB 92 (shown here in several photos) works great for both visual use (including with a binoviewer) and for photography. It is portable and easy to set up, important as you get older and have less ambition and energy to set up complex gear! Apo refractors are the one kind of scope that work great both visually and photographically — all reflectors have to be optimized for one or the other use: Do you want a small secondary for maximum visual contrast, or a large secondary for maximum field illumination of a camera sensor? All reflectors are either compromises, or are best suited only for the one purpose. The Astro-Physics Traveler I have (a 105mm triplet apo no longer made) would fall into my "top-pick" category as well, though it isn't quite as bino-friendly as the TMB. But to my astonishment no one has yet produced a top-class triplet 4-inch apo as compact and lightweight as the Traveler (even the TMB 92 is a bit heavy and large for its aperture). In my opinion too many 4-inch apos produced today, though terrific optically, are still longer, slower, larger and bulkier than they need to be, with big rings that have to be removed to allow the scope to collapse to minimum size. That's a clunky design. No one has copied the Traveler’s elegant compact tube design and integrated tube rings. Is someone in China listening? 某人在中国听着？我们想要协定，头号4英寸f/6复消色差的折光器。 So in the end I'd opt for a 4-inch-class f/5 to f/6 triplet apo as my one “perfect” telescope above all others, especially if it is compact and light. But the choice of the perfect scope certainly depends on location, location, location. And whether or not you have an observatory to allow a big scope to remain set up. And ... on whether you want a scope for both visual and photo use, something only apo refractors do well. If you can settle for just a visual scope, a portable Dob is ideal (and there are many great ones to pick from now, from Meade, Orion and Sky-Watcher). On the other hand, the other night I set up my 8-inch GPS Celestron Schmidt-Cass and had a lot of fun wandering the sky with it. The Go To was great! Brought me back to the days of my youth doing the Messier and Finest NGCs with my old 1970s orange-tubed C8. When you had to work to find things! For me, having Go To is almost essential in my lazy old age. So a new generation of affordable mass-produced Dobs with Go To and tracking will be very welcome (they are promised for later this year) ... if they work! Again, China should be listening! But ... you still can’t beat an 8" SCT for aperture, portability and versatility for all viewing. It’s just that I don’t recommend them for the photo-obsessed — I view them as visual scopes, and good for lunar and planetary imaging. They have way too much focal length and are too slow for deep-sky photography for most people starting out in imaging. By the time you get really obsessed with imaging, you’ll want something more sophisticated for long-focal length deep-sky shooting (if you get that obsessed — in 30 years of imaging, I never have), and on a much better and more costly mount. One of the new low-cost Ritchey-Chrétien scopes now coming out of China (from Orion and Astronomics/Astro-Tech for example) look appealing for the deep-sky imager after galaxies. Whereas, as we promote in Chapter 13, a small 3- to 4-inch apo on a decent smaller affordable mount will always have a place in any astrophotographer’s arsenal. It’s what I use and recommend for the photo ambitious. Everyone starts out their astrophoto career with a big fork-mounted SCT, seduced by the ads, and soon realizes they aren’t well-suited to the task. So I can see why there is such a profusion of good quality 4-inch apos on the market, most from China or Taiwan, many similar to each other, as they do represent an excellent choice, for visual and photo use. They are good choices for serious beginners, but probably appeal more to the person who has owned lots of scopes, has been cured of aperture fever, and realizes they aren’t going to get world-class images of galaxies with their 8" fork-mounted SCT. That’s my pick for the perfect telescope! — Alan Dyer$ shapeimage_3_link_0

04/26/09

The TMB 92mm triplet apo refractor offers an ideal combination of visual versatility (it works with a bino viewer, left) and photo capability as a fast wide-field astrograph, on a suitable equatorial mount (the Astro-Physics Mach 1 is shown as are some sample images).

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