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Telescope Buyers' FAQ - Part One

What is the single most important thing I should know before buying a telescope?

This is the single most important thing you should get out of this FAQ: do not buy your telescope from a department store. Ignore everything any literature tells you about magnification and such. Buy from a telescope store, where you will get a telescope that makes smaller claims, but will give you FAR better performance.

The reason is that as far as telescopes go, how much you can magnify is a function of the amount of light the telescope receives, which is almost entirely determined by the telescope's aperture (the size of the lens or mirror that points at the sky). As far as magnification goes, you can expect 50x per inch of aperture on a normal night.

Department stores always show little 2 and 1/4 inch refractors from $125+ and say that the refractor can get up to a whopping 600x or so. Strictly speaking, this is true. However, applying the 50x rule, it is easy to see that 125x would be pushing the optics, and that is assuming that they were high quality ones. With the quality of the parts they usually give, you are lucky to get 100x with reasonable resolution.

Recommendations for Beginning Amateur Astronomers

Occasionally, amateur astronomers ask for recommendations about telescope buying, learning the sky, and so on. Here are some thoughts.

(Let me state credentials. I am primarily a visual observer: over 40 years I have logged about 6000 observations of nearly 3000 objects, and used perhaps thirty telescopes and binoculars enough to know them well. I have made roughly ten optical surfaces to 16-inch diameter (a sphere - my biggest paraboloid was 8 inches). My forte is deep-sky work; observations I am proud to include the Sculptor Dwarf Galaxy (10x70 binoculars), Maffei I and Leo II (Celestron 14), and S147 (6-inch Maksutov). My interests led to a physics PhD, studying the interstellar medium from a spacecraft: By training I am an astrophysicist, but I maintain amateur status in visual wavelengths - my thesis work was in extreme ultraviolet.)

What to do First
First, some meta-advice. Written words do not substitute for experience. Join an astronomy club, go to observing sessions, and try other peoples' telescopes. You will learn a lot, and will find people who like to discuss equipment and observing.

To find clubs, ask at science stores, museums, planetariums, and the like. Physics and astronomy departments of colleges may know, though clubs aren't strictly their line. Two popular astronomy magazines, Astronomy and Sky & Telescope, publish annual directories of clubs, stores, observatories, and such. Look for them on newsstands, or go to a library and read back issues, or try their web pages.

Been to a club already? Honest? Okay, you can keep reading...

Some Basic Questions
In buying a telescope, you face bewildering, expensive choices. To help deal with the confusion, here are some questions to ask yourself:

  1. How much effort are you willing to put into learning the sky? If you know the constellations, and have practiced finding things by 'star-hopping' - using charts instead of dial-in or punch-in coordinates - you will be able to use a telescope cheaper, smaller, lighter, and easier to set up than one using precise alignment or computer control to locate objects.
  2. How much effort are you willing to spend on your observing skills? Seeing fine detail in celestial objects, or just seeing faint ones at all, requires practice and special knowledge. Yet the rewards are enormous: An experienced observer may see things with a small telescope that a beginner will miss with one five times larger, even with objects and sky conditions that favor both telescopes equally.
  3. How far will you have to lug your telescope to get it from where you keep it to where you use it, by what means, and how much effort will you put up with to do so? Differences in size and optical design create vast differences in telescope portability, and any telescope that you take out and use will be far better than one that sits in the closet because it is too heavy or too cumbersome.
  4. Some people are into technology for its own sake, without regard to whether it is useful or cost effective. Are you willing to pay extra for sophisticated features, even if you don't need them? If so, fine - lots of us like neat equipment. But if not, take care technology enthusiasts don't sell you things you don't need.
  5. Do you want to take photographs or CCD images of celestial objects? 'Astrophotography' is an expensive word. I am not into this side of the hobby, but friends who are typically take several telescopes and several years before they are satisfied, and spend lots more money than visual observers do.

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Author: Dennis Bishop

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