How to Choose a Telescope
S&T's Guide to Telescope-Buying
This is an abridged version of an article that was originally published in 2002 in SkyWatch, our annual publication. Everything in the article is still valid, but the emphasis would probably be different if it were written today. In particular, Go To drives have become much cheaper, better, and easier to use over the last 9 years.
If you want a somewhat longer article that you can print out and read at your leisure, click here to download "What to Know Before You Buy" from SkyWatch 2010 as a 2-megabyte PDF file.
This is an exciting time to become an amateur astronomer. Never have novice stargazers been presented with such a vast array of telescopes and accessories to pursue their hobby. Naturally, this brings the burden of choice: the bewildering variety makes it hard for an uninformed consumer to make the right decision.
Whether you're seriously considering buying that first telescope or just daydreaming about it, this guide will help you narrow your options. First we'll explore the types of telescopes available, and then we'll discuss their key features the size of the primary lens or mirror, type of mount, portability, computerization, and accessories. We'll also look at the tradeoffs, because every instrument has its advantages and disadvantages.
Before you buy anything, you must determine what's important to you. What do you most want to look at? How dark is your sky? How experienced an observer are you? How much to you want to spend? What storage space do you have, and how much weight do you want to carry? Answer these key questions, familiarize yourself with what's on the market, and you'll be well on your way to acquiring a scope that will satisfy you for many years to come.
Before examining the different telescopes available, it's worth knowing the basics of how they work.
The most important aspect of any telescope is its aperture, the diameter of its main optical component, which can be either a lens or a mirror. A scope's aperture determines both its light-gathering ability (how bright the image appears) and its resolving power (how sharp the image appears).
What does this mean? The bigger the aperture the better. With a 6-inch telescope you can discern craters on the Moon as small as about a mile across half the size of those visible in a 3-inch scope (under the same conditions using the same magnification). The same two instruments turned toward a faint galaxy on a moonless night would tell an even more dramatic story. Because the surface area of a 6-inch mirror is four times that of a 3-inch mirror, it collects four times as much light, meaning the galaxy would appear four times brighter. (Astronomically speaking, that's 1.5 magnitudes brighter.)
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