First telescope


You’ve all heard it: “You’re into astronomy? I’m thinking about getting my [kid|husband|wife|2nd cousin] a telescope, what should I get?”

NOTE: I’m providing links to a particular on-line company, simply because they have a lot of different equipment, and have a good reputation. There are other places to purchase, so feel free to do some exploring on your own. A good place to pick up used equipment is the classified section on astromart.com.

The best advice I’ve heard for picking out the first pieces of astronomical equipment are: A) Don’t get a telescope, get a good pair of binoculars and B) get a $10 plastic planisphere to go with the binoculars (ok, it’s $10.95 not including shipping).

Consider: It can be a big hassle to get the telescope out, set it up, and start observing. With the binoculars, you can carry them around with you for spur-of-the-moment viewing. They tuck nicely into a corner of the car trunk, or in a cubby in the RV or boat. They (usually) cost a lot less than a telescope, and a good pair of binoculars (like the 10×50 wide field) can be used for bird watching, boating, or just looking at the scenery as well as astronomy. The amount of light gathered by two 50mm objective lenses is about the same as a telescope with a 3-inch objective, which is not huge, but it’s a lot better than your eyes, and is better than Galileo had. You can see quite a bit with 10x50s. I carry a pair of 10x65s I picked up on sale for $35 at the local sporting goods store in my telescope case.

If you’re ready to step up from the binocs, then I’d suggest a good inexpensive Dobsonian with a 6″ – 10″ aperture. An 8″ telescope is ideal as a beginner scope, but it will carry you through years of viewing. An 8″ f/4 is going to be less than 3 feet long, so its compact enough to take with you easily, but big enough to pull in some of the dimmer objects. Here’s an 8″ f/6 for under $400.

The aperture (the size of the primary mirror or lens) of the scope controls how well you can see dim objects. The dimmest object you could see with a telescope under ideal conditions is called the limiting magnitude. There’s a handy online calculator at http://www.go.ednet.ns.ca/~larry/astro/maglimit.html. If I plug in an 8″ aperture at 100x, and my age (leaving the rest alone) then it says I should be able to see objects down to about mag 14. If I plug in 3.3″ (or 1.5″ for one eye) for the 10×50 binocs above, it tells me I should be able to see down to about mag 9.5. Realistically you should divide these numbers by 2 or 3 depending on the amount of light pollution you have.

STAY AWAY from the high tech scopes, especially at the beginning. You’ll get more usage and enjoyment out of equipment that is simple to set up and use than you will out of the computerized GOTO telecope that takes 30-45 minutes to dial in each time. Even in non-computerized telescopes, the big expensive mounts can be a real hassle for not much benefit for the casual observer. See this post for a funny explanation of why.

Also stay away from huge apertures at the beginning. Unless you’re willing to spend thousands of dollars on the scope, as you go up in aperture, the scope gets longer and longer. The permanently mounted Challenger telescope at Fremont Peak is a 32″ f/4.8, and is twelve feet long! The sweet spot for a newtonian reflector is f/4 to f/8. Below f/4 the visual aberration called ‘coma’ becomes severe. Above f/8 and the telescope is long and unwieldy. The 8″ f/6 above is about 4 feet long. A 12″ f/6 would be 6 feet long. The manufacturers will crowd the f/4 mark to keep the length down at the expense of more severe coma. Unless you go to a different design (i.e., more expensive) telescope like a catadioptric, or RC you’ll have the aperture/length problem. See my FAQ (incomplete, but still useful) for more information on various types of telescopes.

Bottom Line: Consider binoculars first. An inexpensive planisphere is essential when starting out. A 6″-10″ dobsonian mounted newtonian telescope will pull in beautiful sky views, is easy to set up, and won’t cost you a second mortgage. Stay away from the whiz-bang stuff, especially at first, it’s a hassle, it costs too much, and it takes time away from your viewing. Consider used equipment to keep the costs down.

Links:  In case you doubt my word on this subject, here’s what other people have to say about choosing your first telescope:

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