6"... of what?

The most important factor in determining a telescope's performance is the aperture, or the diameter of the main light-collecting element. Whenever someone refers to a telescope of such-and-such a size (e.g. 8" or 120mm), that's the aperture they're referring to.

Most people can understand that a larger aperture gathers more light, and so produces brighter images -- important for spotting dim nebulas or faint stars. What many newcomers don't know is that a larger aperture also produces more detailed images as well. Increasing aperture improves a telescope's resolving power -- its ability to separate small details (such as two close stars or small patches of color on a planet's surface or clouds). Because of these two factors, experienced observers generally recommend getting as large an aperture as you feel comfortable with.

As a general rule, newcomers are best served getting a telescope with an aperture of at least 4" or 100mm. There are some very fine telescopes of smaller apertures, but newcomers will generally find the views of celestial objects more satisfying with at least 4". Above this limit, personal preferences come into play. For example, if you want a significantly larger telescope (say, an 8") for seeing faint objects and squeezing maximum detail out of bright ones, a Dobsonian reflector is a good choice, since it's the cheapest good-quality telescope design. If portability is more important than sheer aperture -- true for many urban dwellers, or people with limited time -- than a smaller but more easily moved telescope may be worth considering. A 4" or 5" telescope that gets used regularly will be more satisfying than a 15" telescope that sits in a closet all the time! So spend some time investigating your preferences and needs, and then (generally) choose the largest telescope that's consistent with those.

Back to my suggestions to newcomers

Last Modification: August 23, 2004