Buying Your First Scope

Buying Your First Scope

A telescope need not have high magnifying power or be expensive to allow you to see every planet in the solar system. It is the size of the lens aperture and the instrument’s portability that count. John Shibley, an editor at Astronomy magazine and author that publication’s annual telescope buyer’s guide, has these tips on equipping yourself to scan the heavens:

Focus on a telescope’s lens size: A lot of people ask, “What power is that scope?” Actually, magnification is irrelevant. What matters is the amount of light a telescope gathers, which depends on the size of the mirror that brings light to a focus or the size of the lens itself. The bigger the mirror or the lens, the fainter the objects you will be able to see and the better the resolution. If you don’t have a large aperture, you crank up the magnification and it just ends up stretching an image that is not any good to begin with.

Image: Elena

Start with a reflecting scope: There are two types of telescopes: reflecting and refracting. A reflecting telescope costs about half as much as a comparable-sized refracting telescope – it is excellent for star and nebulae observations and for use in astrophotography. The refracting telescope tends to distort images less and is good for lunar and solar observation. It can distort color, though, and can be difficult to move, which may turn off beginners.

Know your mounts: A scope in the $800-$1000 range has a Dobsonian mount, which means the scope can be pivoted up and down and left and right but can’t be calibrated to line up with the earth’s axis so that it automatically follows the stars. More expensive scopes come with equatorial mounts – they are the ones that actually track the sky.

Get several eyepieces: Usually you want to get three eyepieces. That is because observing the moon requires a low magnification, planets a medium magnification, and the stars a high magnification. Any eyepiece with a focal length in the upper 20s to lower 30s in millimeters is considered low-powered; from the mid-teens to the lower 20s is medium-powered. Anything lower than 12 mm is high-powered. Having more than one eyepiece allows you to adjust to atmospheric changes that may make objects look blurry.