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Telescopes buying guide

Choose the right astronomy telescope for you

When you begin searching for a telescope, you might be tempted to go for the biggest telescope with the largest amount of magnification. That’s not always the way to go. It’s important to find the type of telescope that matches the kind of viewing you’re going to be primarily engaged in, so you’ll need to know a little bit about how they work.

Choose the right type

There are three types of telescopes commonly used for home astronomy. There's no right or wrong choice — each type performs a little differently, so what you plan to do with your telescope will determine which type you choose.

light path in a refractor telescope

The objective lens on a refracting telescope focuses light to form an image that can be viewed through the eyepiece.

Refractors are rugged and easy to maintain. The front lens (the objective) focuses light to form an image in the back, where the eyepiece is. They produce crisp, high-contrast images that look good at high magnification, but may be larger and less portable, and come at a higher cost.

cutaway view of a reflector telescope

Reflector telescopes use mirrors to gather and focus light.

Reflectors use mirrors to gather and focus light. The type known as a Newtonian reflector (invented by Sir Isaac Newton) offers sharp images with good contrast in a shorter, more easily transportable optical tube. The Dobsonian is a reflector on a very simple, very rugged mount. Dobsonian telescopes are popular for their relatively low cost and ease of use.

cutaway view of a catadioptric telescope

Catadioptric telescopes employ lenses and mirrors to form an image.

Catadioptric telescopes employ both lenses and mirrors to form an image. In their commonly encountered forms (the Schmidt-Cassegrain and Maksutov-Cassegrain), catadioptric telescopes are very compact. This allows you to obtain a large-aperture, long-focus telescope that's very transportable.

Once you’ve decided what type of objects you’ll be looking for in the sky, how much you want to spend, and how portable you want your setup to be, one of these types should stand out as an obvious choice.

Let some light in

Each telescope will have an aperture size listed in millimeters. This tells you how much light will enter the telescope through the lens at one end. The larger the aperture, the more light comes in. If you’re looking at distant, deep-sky objects like galaxies or nebulae, a large aperture is a must — you need to gather in as much light as possible to see them in the night sky.

Planetary objects in our solar system reflect quite a bit of light from the sun, and may be a bit overwhelming with a large-aperture telescope. Special polarized filters can be added to the eyepiece of the telescope to help with contrast and clarity.

Add magnification for a closer look

The aperture gathers light so you can see what’s out there. The eyepiece you put in the other end of the telescope is what determines the amount of magnification you’ll get. The focal length of the scope divided by the focal length of the eyepiece gives you the overall magnification factor you can expect. If you have a 1,000-mm focal length scope, used with a 25-mm eyepiece, then 1,000 / 25 = 40x magnification.

How much magnification you need depends on what you want to look at, and how closely. Eyepieces are made to be removable, so you can spend some time looking at individual craters on the surface of the moon with high magnification and then swap in an eyepiece with medium magnification to fill your vision with Saturn and its rings in full frame. Celestron sells individual eyepieces, as well as a handy all-in-one Observer's Accessory Kit that includes several eyepieces and filters.

Celestron CPC Deluxe 1100 HD Telescope

Celestron CPC Deluxe 1100 HD telescope with altazimuth mount and additional astrophotography wedge.

Mounting makes a difference

A telescope needs a solid, stable mount, so that your image will not be blurred by vibrations. A smooth panning motion will help you track across the sky in search of new stars and planets. There are two common types of mount:

An altitude-azimuth (altazimuth) mount operates like a tripod's pan-and-tilt head, moving the scope up-down (altitude) and left-right (azimuth). If you're intending to use a small telescope for casual sky viewing or daytime use (say, birdwatching), you'll find the altazimuth mount preferable. Well-engineered mounts of this type will have finely threaded slow-motion controls that enable the scope to be moved smoothly by tiny amounts.

An equatorial mount automatically adjusts for the Earth's rotation. It's far easier to track a celestial object with a scope mounted this way, since you need only concern yourself with turning the scope about one axis — not two simultaneously, as in the alt-az. These mounts make astrophotography much easier.

If photography is your goal, you’ll require a t-adapter that allows your camera to attach to and shoot pictures through the eyepiece. Some are camera-specific, others are considered to be universal. Some telescopes require an optional wedge for astrophotography.

Explore with computer guidance

Many amateur astronomers prefer to manually control their telescopes and learn astronomy the old-fashioned way. Modern inventions have made it much easier to search the sky, which can be fun for beginners. Many scopes come with a database of known objects, so you can select one you want to see, and let the telescope find it for you.

Motorized telescopes have moving mounts that are controlled directly by a built-in guidance system or remotely by a connected PC. This allows you to direct the scope to any object in the computer's database, and can keep your telescope tracking with the Earth’s rotation during prolonged viewing. This feature is especially useful in astrophotography.

Many basic telescopes can be upgraded with Wi-Fi and GPS modules, allowing you to add features as you go.

Armed with this basic knowledge, you can choose the right telescope for your needs and get started on your night-sky explorations right away.

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