12 Rules for Buying a Telescope

Many people consider buying a telescope for themselves or giving a telescope as a gift. But, it's not easy to buy a good telescope. Over the past few years in the amateur astronomy hobby, I've learned a few simple rules that might be helpful. If you know these rules, it'll be much easier to consider any telescope purchase.

1.The aperture (diameter) of your telescope determines how much light it can collect. The more aperture you have, the more likely you will be to see faint celestial objects. Many amateur astronomers recommend starting out with a telescope that offers and objective that is 6 to 8-inches in diameter.

2.Magnification helps discern detail on the moon and planets like Mars, Jupiter, and Saturn. But, aperture helps with seeing faint deep space objects (DSOs) like galaxies and star clusters. Generally, quality telescopes are not advertised by the magnification they can deliver.

3.The most magnification that your telescope can practically handle is 50 x Aperture (in inches). So, my 2.8 inch (70mm) telescope has a maximum practical magnification of 140x. If someone says a 60mm telescope is capable of 575x magnification, they are exaggerating. You probably won't be able to see anything at that magnification.

4.For any given eyepiece, the magnification provided is the focal length of your telescope divided by the focal length of your eyepiece in millimeters. So a 25mm eyepiece provides 28x magnification on a 700mm focal length telescope.

5.Longer telescopes can handle more magnification for looking at the moon and the planets. Shorter telescopes often offer a wider field of view for low magnification views of deep space objects.

6.When buying a telescope, it is best to buy a quality name telescope (at least an Orion or Celestron) via a specialty store. Reputable stores often advertise Sky & Telescope or Astronomy magazine.

7.If you buy a telescope, make sure it can handle 1.25 inch diameter eyepieces. Many older cheap department store telescopes come with .965 inch diameter eyepieces. It's hard to find high quality replacement eyepieces in this size range.