[Virginia Tech Department of Physics]

A Dobsonian telescope (credit)

Thinking of buying a telescope?

I recommend buying a Dobsonian telescope

Unless you would be using the telescope to take pictures with an attached camera, then the best telescope (and a "best buy" in the sense of "bang for the buck") is a Dobsonian telescope. We use these sorts of telescopes in our Introduction to Astronomy lab courses. For that matter, I own and use one myself. People 10-80 years old can easily use this sort of telescope. If you are an experienced amateur astronomer, you might consider buying a fancier type of telescope with lots of bells and whistles, but then if you have that level of experience you don't need my advice.

A Dobsonian is a reflecting telescope (uses a mirror, not a lens) in the same design as a Newtonian telescope (concave collecting mirror is at the rear of the telescope tube, eyepiece is on the side of tube, up near the front). The Dobsonian name comes from the design of the mount structure --- it holds the tube like a toy cannon, allowing it to easily swivel up and down, and left and right (see picture above). The mount is very simple in construction, typically wooden, but very, very stable, easy to set up, and easy to use. This mount (designed by John Dobson, hence the Dobsonian name) is far, far better and far cheaper than any other relatively inexpensive mount on the market. Depending on the size of the collecting mirror, a commercial Dobsonian will cost a few hundred to about $500 dollars. "Fancier" telescopes costing $2000 dollars or more, mostly due to the cost of the fancier mount, will typically be more difficult to take out and set up, more difficult to use, less stable (they shake when you touch them), and more frustrating in general. These more expensive scopes (for the same size optics!) *may* allow you to take photographs --- if you buy additional accessories and spend a great deal of time properly aligning the mount with the north star, and can stand the lengthy period of frustrating results, typically caused by the instability and difficulty of using the mount. On the other hand, if all you want is to *see* things (planets, stars, star clusters, nebulae, galaxies,...) then the Dobsonian is the best thing to use. In minutes you can take it outside, set it up, and view things with ease, for as long as you wish.

Two caveats... First, a Dobsonian is not computer controlled (a great expense anyway), so you need to figure out where to point it to see things. If you want to look at the Moon, and planets, this is typically not an issue. To find more subtle things will require some maps and a little learning about the sky --- which can be loads of fun of course (and maybe even much of the reason for having a telescope). For that matter, at a recent sky observing event I attended there were many Dob users easily enjoying the sights while one fellow spent hours trying to set up his expensive computer controlled telescope, which had a smaller mirror anyway and gave an inferior view when he finally got it to work. Second, you should get a Telrad device for mounting on the side of the tube (costs around $40). This device is a "one-power" finderscope that, when viewed through, seems to project a bulls eye pattern on the sky. After aligning the pattern with your telescope's view (simply done on a distant light pole), you can easily point the telescope at any bright object (center it in the bulls eye), and even point at locations where you know something is "hiding" (a faint nebula) given your sky maps. The Telrad is very simple to use; you don't even need to put your eye up right behind it as you can see the bulls eye pattern from distances up to a foot or so behind the device. (When using the Telrad you're looking through a piece of glass onto which has been projected the bulls eye pattern; the pattern seems to be projected on the sky --- it's in focus with the stars and remains put on the sky showing the location the telescope is pointing at, even if you shift your head back and forth). The Telrad is a must for Dobs, in my opinion. In the picture at the top of this page the black rectangular box on top of the telescope tube is a Telrad.

There are a number of manufacturers of Dobsonians: Meade, Celestron, Orion,... All are good. Go to a local bookstore or library and pick up a copy of Sky and Telescope magazine. In it you will find adds from these companies. They may have fancier names for their version of a Dob, but you'll know one when you see one. You can also look on the internet for companies selling Dobs. By the way, some people construct their own Dobsonian mount, which is generally just as good as any commerical Dobsonian mount (picture at the top of the page is of someone's homemade Dob).

John Simonetti's homepage | Virginia Tech Physics