If you’re wonder how to choose a telescope there are a lot of factors worth considering. Telescopes are not inexpensive, so you want the best instrument for your needs. Here are tips and questions you need to answer before you buy. In particular, learn about the difference between reflectors and refractors and the types of telescope mounts, as well as their pros and cons.
How to Choose a Telescope for Your Needs
First, you need to answer some questions. There are no right or wrong answers, but once you identify your needs you’ll have an easier time choosing a telescope.
- What is your price range? A good telescope ranges anywhere from a couple hundred to several thousand dollars.
- What do you want to look at? Pretty much any telescope works great for viewing the Moon, planets, galaxies, nebulae, and clusters. But, there are differences. Reflector images are upside-down and may suffer spherical or coma aberration (tiny round objects don’t look round). Refractor images are right side-up, but they have chromatic aberration (fringes). Round objects look round though. Reflectors shine for viewing near objects, while refractors excel at deep sky imaging.
- Are you willing to do maintenance? Reflectors require cleaning and collimation, while refractors are enclosed and pretty maintenance-free.
- Do you plan on taking pictures? All telescopes can accept a camera mount, but you’ll want a scope that tracks if you plan on taking long exposures.
- How much storage space do you have? Consider the footprint of the telescope. Bigger may not be better.
- Will you travel with the telescope? Refractors can be long, while reflectors can be wide and heavy.
- How dark is your sky? Aperture size determines the amount of light you capture. A larger aperture helps you see dimmer objects.
Reflector vs Refractor Telescope
The two broad types of telescopes are reflectors and refractors. A refractor is a long tube with an eyepiece at one end and a lens at the other end. A reflector uses one or more curved mirrors that reflect light and form an image. Most of the major optical telescopes astronomers use in observatories are reflectors. There are several designs. In some cases, the eyepiece is at the end of the telescope. In other reflector telescopes, the eyepiece is somewhere along the length of the tube.
There are pros and cons for each type of telescope. The one you choose depends on which factors matter most to you.
| Category | Winner | Reason |
|---|---|---|
| Price | Reflectors | Refractors are the best value for small telescopes. Reflectors collect a lot of light, as mirrors are more affordable than large lenses. So, reflectors are much more affordable for larger apertures. |
| Maintenance | Refractors | Reflectors require periodic mirror alignment and cleaning. |
| Size/Portability | Depends | Refractors get unwieldy and long at high apertures, while reflectors get wide and heavy. Either way, there is such a thing as too big. |
| Optical Performance | Depends | Optical performance greatly depends on the manufacturer. Quality refractors and reflectors yield excellent images. At lower price points, refractors have chromatic aberration, while reflectors have spherical aberration. |
| Visual Astronomy | Reflectors | Reflectors excel for visual astronomy because you get a large aperture at a lower price. This means you can see distant objects. Also, color fringes are more visually distracting than shape distortion. |
| Astrophotography | Refractors | Smaller refractors are more affordable and work fine for astrophotography because they collect light using long exposures and tracking mounts. |
The Type of Mount Matters
You can mount a small refractor on a camera tripod. This type of mount for a telescope is an altazimuth mount because it moves vertically (altitude) and horizontally (azimuth). The other major type of mount is an equatorial mount, which is easier for manually tracking the movement of objects in the sky. Computerized tracking is available for both types of mounts. But, you should decide whether you need tracking before you buy a telescope because you can’t always upgrade later. As you might imagine, a tracking mount increases a telescope price.
Choosing Eyepieces for Your Telescope
A new telescope comes with at least one eyepiece and often more than one. The telescope’s magnification depends on which eyepiece you use, plus you can get filters that improve viewing.
Unlike most things in optics, most telescopes use a standard size, which is 1.25 inches. Even so, it’s a good to check the eyepiece size before you buy a telescope so you know what size you need.
Eyepiece magnification depends on its millimeter rating. The smaller the number, higher the magnification. But, more magnification is not always better! If only one eyepiece comes with the telescope, it’s usually a 25-mm or 20-mm one. This size is good for viewing the Moon, planets, galaxies, clusters, and nebulae. A larger size (e.g., 32-mm) lets you see the entire full moon, the sun (with a solar filter), and a larger section of the sky. A smaller size (13-mm, 8-mm, 6-mm) gives you higher magnification, but it’s harder to see through smaller lenses and they result in a dimmer image. Higher magnification lets you see the moons of the gas giants and greater detail for the objects visible with the larger lens.
A Barlow lens combines with an eyepiece and doubles its magnification. So, this lens is worth having in your kit. Also consider getting a moon filter because the full moon is blindingly bright in a telescope. A T-adapter lets you attach a camera to the telescope. There are also mounts for cell phones and optical sensors, if you prefer taking pictures that way.
Eyepieces and filters come separately or in kits. If you want a good selection from the start, remember to include them in your budget.
How to Choose a Telescope – The Bottom Line
The bottom line is that there is no one right choice for a telescope. Both reflectors and refractors have their place and which you choose depends on your needs. The type of mount is another important consideration, since it determines how easily you view objects at different angles and track them. Above all, choose a reputable manufacturer. Examples include Celestron, Orion, Meade, Gskyer and Skywatcher. Research a prospective purchase and read reviews. Sometimes you’ll see quality telescopes in stores (usually not so much). Most of time, you order a telescope online.
References
- Andersen, Geoff (2007). The Telescope: Its History, Technology, and Future. Princeton University Press. ISBN 978-0-691-12979-2.
- Lipson, Stephen G.; Lipson, Ariel; Lipson, Henry (2010). Optical Physics (4th ed.). Cambridge University Press. ISBN 978-0-521-49345-1.
- Pasachoff, Jay M. (1981). Contemporary Astronomy (2nd ed.). Saunders Colleges Publishing. ISBN 0-03-057861-2.
- Vasiljević, Darko (2002). “The Cooke triplet optimizations”, in Vasiljević, Darko (ed.). Classical and Evolutionary Algorithms in the Optimization of Optical Systems. Springer US. doi:10.1007/978-1-4615-1051-2_13