So, you want to buy a telescope

Posted: October 18, 2017 in Science
Tags: , , , , , , , ,

Telescopes are incredibly cheap nowadays. Taking inflation into account, they cost maybe 15% of what they did 50 years ago. Back then, it made sense to build your own ‘scope.

I did — a 6″ f10 reflector mounted on a 2X4 in place of a tube with a homemade Ramsden eyepiece and an altazimuth mount made from 1.5″ pipe. Total cost was about fifty bucks in 1960s dollars.

That’s equivalent to maybe $300 today. And for that $300 you can buy a much better ‘scope than my first reflector. Hell, you can buy a better ‘scope for half that. Why? Chinese mass production. The quality of the ‘scopes they make varies, but overall is pretty good, especially for the price. Nowadays, it’d almost certainly cost you more to build a telesceope than to buy one of equivalent size and quality.

Which brings us to the question in the headline: Assuming you’re a novice, what should you buy, and why?

  • First, stay away from telescopes with shaky mounts. The most common culprits are cheap 60mm refractors, which often cost under a hundred bucks new; but their inadequate, shaky mounts make observing miserable, often close to impossible. You’ll want a telescope with a solid mounting, which is probably the most important feature of a good telescope.
  • Second, buy a ‘scope with a 1.25″ focuser and eyepieces. Cheap 60mm refractors commonly have .965″ focusers and eyepieces, and the eyepieces are uniformly terrible (almost always Huygens eyepieces with chromatic aberration and a narrow field of view); almost worse, it’s difficult to find decent eyepieces in the .965″ size, so cheap refractors with the .965″ focuser and lousy eyepieces (and shaky mounts) are all but useless. They’re so bad that they discourage a lot of people from taking up astronomy as a hobby.
  • Third, do not buy a go-to computerized ‘scope. The equatorial-mount types are a pain to set up, and even when you do set them up correctly (polar axis aligned with the north celestial pole, so they’ll track) you’ll never learn the night sky if you rely on them. Essentially, they’re a crutch for those too lazy to learn the constellations and where the planets and deep sky objects are. Laziness is its own punishment, and those who buy go-to ‘scopes get what they deserve: disappointment and money loss. There’s a reason there are so many nearly new go-to ‘scopes on craigslist offered for a fraction of their price new.
  • Fourth, buy used. There are almost always good buys on your local craigslist, where it’s common to find ‘scopes in good shape selling for 20% to 50% of their cost new. You can get a great ‘scope for under $300 (sometimes for under $100), which is about the most a novice should consider spending.
  • Fifth, buy a decent pair of binoculars and acquaint yourself with the night sky before buying a ‘scope. I’d recommend 10X50s (10X magnification with 50mm lenses), which won’t break the bank but will provide a wide field of view and enough light-gathering surface and magnification that you can see a lot of the brighter deep sky objects — a few will look great, though most won’t look like much; but you’ll know where they are.
  • Sixth, get a good planetarium program for your computer and use it to find the constellations, planets, and deep sky objects. The best planetarium program, Stellarium, is free, and works on all platforms.
  • Seventh, once you’ve become acquainted with the night sky, buy a Dobsonian altazimuth-mount reflector. You get more bang (inches of aperture) for the buck with a Dobsonian, and for casual viewing they’re easier to use than equatorial-mounted ‘scopes. (Yes, you’ll want an equatorial mount if you ever get into celestial photography, but that’s way down the line for most novices.) You can commonly find 8″ or 10″ Dobsonian reflectors on craigslist for $150 to $300, sometimes less. Helpful hint: before buying a ‘scope, make sure you can carry it around easily. If your ‘scope is a pain to move, chances are you won’t use it much, if at all.
  • Eighth, if your ‘scope doesn’t come with eyepieces included, you’ll need at minimum two: a low-power wide-field eyepiece plus a medium-high power eyepiece, and maybe a medium power eyepiece. For the wide-field eyepiece, get one in the 25 to 32 mm focal length range, for the medium power 12 to 15 mm focal length, and for the medium-high power 8 to 10 mm focal length. (There’s not much point, at least for casual observers, in buying high power eyepieces in the 4 to 6 mm range; they drastically narrow a ‘scope’s field of view; they greatly magnify any shakiness in the mount, resulting in wavering, unsteady images; and you need very good seeing conditions to use them to any advantage at all.)
  • Ninth, make sure to buy decent eyepieces (probably Plossls or Kellners, both of which are cheap, good and plentiful), and under no circumstances buy a Huygens eyepiece (the type commonly included with 60mm refractors). You can buy good quality Chinese Plossls and Kellners on eBay for under $10, and Surplus Shed currently has a nice 30mm Kellner for $12. (On eBay, the variety of focal lengths is usually limited; at the moment, there are 10mm Plossls available for about $6.50, and all but useless 4mm Plossls for the same price; the good news is that if you watch over months you’ll likely find what you’re looking for at about the same price.)
  • Tenth, do not spend a lot of money on eyepieces or other accessories. Some fancy eyepieces cost upwards of a thousand dollars. That makes no sense at all: the point of diminishing returns arrives very quickly (around $15) with eyepieces.
  • Eleventh, if your ‘scope doesn’t come with a Telrad or red-dot finder, buy one and attach it to your ‘scope. Of the two types, Telrads are easier to use, though at $40 they’re more expensive than red-dot finders. Both types are preferable to small finder ‘scopes.
  • Finally, have fun and enjoy the beauty of the night sky. And please remember that your enjoyment will be greater if you take the time to learn the night sky, and don’t just punch numbers into a keypad.
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