How to Buy a Good Telescope

Determine the purpose of your stargazing. As an amateur astronomer, you most likely wish to look at planets and stars. You may also wish to use your telescope for astrophotography.

Decide whether you want a portable telescope or one that will be permanently fixed in one place. The advantage of portable telescopes is you can transport them to stargazing events. The advantage of a fixed telescope is it remains acclimated to the ambient temperature.

Concern yourself with the quality of optics in any telescope you may be considering purchasing. The lenses should not be made of plastic, as this will result in poor image quality.

Consider a 3-or 4-inch lens for your first telescope. The larger the diameter of the lens, the brighter the images will be. A reflector telescope with a 3-or 4-inch lens is most likely to be sufficient for your needs.

Determine which mount will best suit your needs. A go-to mount is a computerized mount. It uses a global positioning system (GPS) to point the telescope to a desired location. The user enters the relevant data into the computerized mount and the telescope finds the object, such as the moon.
A clock-drive mount may also be computerized. This mount will track a designated object throughout a given time period. It moves the telescope, keeping the object in the sightline of the scope. This mount is excellent for astrophotography, as long exposures are necessary.

Determine the sturdiness of the mount of the telescope you are interested in buying. Whether it is a go-to mount or clock-drive mount, it needs to be sturdy enough to hold the telescope in position. An unstable mount results in wobbly images.

Be prepared to purchase one or two quality eyepieces suitable for use with your telescope. Use the following equation (in millimeters) to determine an appropriate sized eyepiece:
Divide the focal length of the telescope by the focal length of eyepiece. The resulting answer is the amount of magnification, or light power, of the eyepiece.

Avoid eyepieces that will give you too high a magnification; the result will be images that are blurry and dim, though they will appear large in your telescope.
Lower magnifications provide crisper, brighter images. It's most likely, given the range of amateur telescope sizes, eyepieces with focal lengths of 32mm or 25mm will suffice.