Telescope buying guide

The Christ­mas shop­ping sea­son is upon us, and a child’s fancy often turns to thoughts of tele­scopes. I’ve had sev­eral requests to expand on my com­ments about tele­scope buy­ing and the acces­sories asso­ci­ated there­with, so here goes:

The sad truth is that most ‘scopes sold at this time of year are not suit­able for view­ing the heav­ens. More often than not, a child’s squeals of joy on Christ­mas day will turn to real tears of frus­tra­tion in January.

First rule: Arm your­self with knowl­edge before you buy. Some man­u­fac­tur­ers and sales­peo­ple make claims that don’t mean any­thing at all and are usu­ally designed to con­fuse the unwary.

Thus, learn the tech­ni­cal char­ac­ter­is­tics and terms con­nected with tele­scopes, or you’ll end up with a piece of junk rust­ing qui­etly in your garage. Also, note that the poor kid prob­a­bly doesn’t have the fine-motor skills or knowl­edge of the sky to find any­thing. Per­son­ally, I wouldn’t buy a tele­scope for any­one younger than 14 or so. Gen­er­ally speak­ing, you’re up, par­ents. Pre­pare to do all the work your­self, at least at the begin­ning. That’s actu­ally a bless­ing in dis­guise. Stargaz­ing should be a fam­ily affair. There’s noth­ing in the world that binds peo­ple together more than a night under the stars.

I can’t tell you all you need to know in this col­umn. That’s what tele­scope buy­ing guides are for. Check out the one at telescope.com, for example.

That said, most of the buy­ing guides are at com­mer­cial sites where they want to sell you a tele­scope at max­i­mum profit. So let’s hit the high spots — the terms and warn­ings you’ll need so as not to get snook­ered by some tele­scope salesperson.

APERTURE is the mea­sure of the light-gathering power of a tele­scope. The more light it gath­ers, the more you can see. Tele­scopes use mir­rors or lenses to gather light from the stars and plan­ets. Tele­scopes that use mir­rors are called reflec­tors. Lens-based tele­scopes are called refrac­tors. Aper­ture is usu­ally expressed as the diam­e­ter of the mir­ror or lens that gath­ers the light. It should be at least six inches in diam­e­ter, or you won’t be able to see much.

Aper­ture is some­times expressed in mil­lime­ters (mm) to con­fuse the issue. A 60mm refract­ing tele­scope sounds so much bet­ter than a 2.6-inch tele­scope, and such tele­scopes are, frankly, junk. The same can be said for most of the avail­able 114mm (4.5-inch) reflectors.

MOUNTING. A tele­scope should be mounted on a sturdy plat­form, which must be beefy enough to keep the tele­scope pointed in the proper direc­tion. The junk tele­scopes men­tioned above are so wob­bly that most peo­ple can’t keep them pointed.

A rel­a­tively inex­pen­sive alter­na­tive is a six-inch reflec­tor on a Dob­son­ian mount. Dob­so­ni­ans use a sturdy wooden cra­dle to hold the tele­scope tube. They look more like siege can­nons than tele­scopes, but they are remark­ably stable.

COST. A usable 6-inch Dob­son­ian tele­scope will cost, at min­i­mum, about $350 includ­ing the cost of the ship­ping. Spend any less on a smaller tele­scope, and you’re wast­ing your money. I know of no place in Cen­tral Ohio that sells qual­ity tele­scopes, but I’d be glad to hear oth­er­wise if some­body wants to tell me so.

If $350 is beyond your means, con­sider a pair of binoc­u­lars and a book on binoc­u­lar observ­ing. Buy the book first. It will pro­vide advice on what kind of binoc­u­lars to buy.

ACCESSORIES. The eyepiece(s) pro­vided with the tele­scope should be mounted in 1.25-inch-diameter bar­rels, not the smaller, cheaper variety.

The find­er­scope (or “finder”) is a small refract­ing tele­scope mounted on the side of the main ‘scope. An absolute neces­sity if you’re ever going to find astro­nom­i­cal objects, the finder should have an aper­ture of at least 30mm (1.18 inches). I pre­fer the 50mm version.

Also, don’t for­get a good set of star maps. (See my Nov. 14, 2011 col­umn for more-detailed advice on that score.)

MAGNIFICATION. Tele­scopes don’t work well at extremely high mag­ni­fi­ca­tion. An astro­nom­i­cal tele­scope will only mag­nify well at 30 “power” per inch of aper­ture. A six-inch Dob­son­ian is rarely used above 180 power. Smaller tele­scopes that adver­tise obscenely high mag­ni­fi­ca­tions (“mag­ni­fies to 400 power!!!”) are stone-cold rip-offs.

APPEARANCE. The man­u­fac­tur­ers of junk tele­scopes work hard to fes­toon their prod­ucts with a lot of chrome knobs and doo­dads. A good, inex­pen­sive tele­scope is large, sta­ble, and rather plain looking.

HIGH PRESSURE SALESMANSHIP. Don’t lis­ten to such claims as, “Bet­ter buy it now. They’re going fast.” They can always order you another one, and it’s far bet­ter to dis­ap­point a child at Christ­mas than to turn her off per­ma­nently to the grandeur of the uni­verse with a junk telescope.

Think three times before lay­ing out any money. In fact, given all you’ll have to learn, by the time you read this, it’s prob­a­bly too late. Start think­ing now about next Christmas.

Above all, call me at 740–363-1257 before you buy. I really mean it. Think of it as a reward for mak­ing it all the way to the bot­tom of this column.

Tom Burns is direc­tor of Ohio Wes­leyan University’s Perkins Obser­va­tory in Delaware. He can be reached at tlburns@owu.edu.

Posted by Tom Burns on Nov 27 2011. You can follow any responses to this entry through the RSS Feed. Comments can be made below.