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Telescopes 101

Fifteen things you need to know before buying a telescope.

11. I would like to buy a telescope, but almost all I see are expensive. Why?

A good telescope is a combination of high-quality optics, machining, electronics, and mechanical controls. Such things aren’t cheap. It takes incredibly expensive, high-precision machinery to grind the curves into mirrors or fabricate lenses. Some lenses comprise up to four separate elements, each with two optical surfaces. And the larger the mirror or lens, the bigger and stronger the supporting tube, drive, and tripod have to be.

Finder scope setup

Align your finder scope during the day. Most observers take time before each observing session to check their finder scope’s alignment. Here’s how:

  • Insert a low-power eyepiece in your telescope for initial alignment.
  • Loosen your scope’s motion-control locks to allow movement.
  • Move your telescope until you center a distant object (the top of a transmission tower, tree, building, etc.). Focus your scope to view the object.
  • Lock down your telescope’s motion controls to avoid movement.
  • Loosen the screw locks on your finder scope’s mounting bracket (see your telescope’s manual), and then position the finder scope so the object that’s centered in your scope also is centered in your finder.
  • Lock your finder scope into position.
  • For higher precision, replace the low-power eyepiece in your telescope with one that provides higher magnification, then refine the alignment.

12. Is there any way for me to "test drive" a telescope?

Yes. Look in your area for an astronomy club, and visit one of its meetings. You'll find others who enjoy astronomy as much as you and are willing to share information and views through their telescopes. At one of the club's public or members-only stargazing sessions, you'll be able to look through many different telescopes in a short period of time.

13. Apart from quality optics, what's the most important thing in a telescope system?

The mount. You can buy the finest optics on the planet, but if you put them on an undersized or poor-quality mount, you won’t be happy with your system. No telescope can function in high winds, but a poor mount will transfer vibrations in a light breeze. The mount’s quality also affects the “damp-down” time. This is the interval between when you touch the scope (to focus, for example) and when the image in the eyepiece stops moving. Sturdy mounts reduce this to a second or two. Bad mounts increase this time to an intolerable length. Mount quality is one more reason to “try before you buy.”

14. Is a "go-to" scope better than one without go-to?

Yes. Once properly set up, a go-to scope (actually, it's the telescope's drive that's go-to) will save you lots of time by moving under internal computer control to any object you select. It's important, however, that you understand how to set up your scope, and that will require you to identify a few bright stars. Use a star chart to make this step easier. Even experienced observers prefer go-to scopes because they make star-hopping to deep-sky objects a thing of the past (when star-hopping, an observer locates a bright star and proceeds to ever-fainter stars until the target is located).

Telescope mounts
An equatorial mount moves in two planes, with one axis pointed toward the North Celestial Pole (NCP) — a spot in the northern sky near Polaris. With an optional motor drive, you can align the mount to the NCP, and the object you are observing will stay in the field of view. If you’re planning to do long-exposure astrophotography or digital imaging, an equatorial mount is essential.

An altitude-azimuth (alt-az) mount moves the telescope horizontal and vertical. A camera tripod is a good example of an alt-az mount.

It can be difficult to tell an alt-az forkmount from an equatorial fork mount. The difference is an equatorial fork mount lines up with the NCP. Fork mounts are popular with compound scopes. You will also find the majority of modern observatories use equatorial fork mounts.

A Dobsonian mount is an alt-az type specifically made for Newtonian reflecting telescopes. The mount, which employs a swivel base and a cradle assembly to hold the telescope tube, has a simple design and is easy to construct (if you choose to build one yourself).

The mount is the second most important component — after the optics — of a telescope system.
Astronomy: Roen Kelly

15. Since telescopes are used outside, do they need electricity?

No, but their motor (go-to) drives do. In most cases, telescope drives use direct current, which means you can either use batteries or obtain an adapter (usually you are given an option) that will allow you to plug into an electrical outlet.

Lighten up
Always remember the best telescope for you is the one you’ll use the most. If it takes an hour to set up a scope, or if your scope is large, heavy, and difficult to move, you may observe only a handful of times each year. If, on the other hand, your scope is quick to set up or if you can mount it permanently (or at least its tripod or pier), you may use it several times each week. A small telescope that’s used a lot beats a big scope in a closet every time.
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