TELESCOPES

An optical telescope is an device that collects light and magnifies the size of the object which is reflecting the light so that it can focus to a point.  Telescopes are used in astronomy and terrestrial observation. If you are interested in buying a telescope, please see our Telescope Buyers Guide for more practical telescope information.  There are three main types of telescopes.  They are as follows:

Refracting Telescope

Reflecting Telescope

Catadioptric Telescope

The difference in these telescopes is in the way they collect and magnify the light.  Telescopes either use mirrors or lenses to collect the light.  A refracting telescope or refractor telescope uses lenses, a reflecting telescope or reflector telescope uses mirrors, and a catadioptric telescope, (such as a Schmidt Cassegrain or Maksutov-Cassegrain) uses a combination of the two.  Each has its advantages and disadvantages. Click on the telescope names above to learn more about each type.

People often ask two questions about telescopes.  One, how much does it magnify?  Two, what can you see in it? For starters, forget the pictures from the Hubble telescope that you have seen.   You will not see anything like that.  Your eyes are not good at detecting faint light, so what you see in the eyepiece, aside from planets will be more or less black and white and small.  When you see bright and colorful pictures, those are taken using CCD cameras with exposures of many hours.  See the astrophotography section for more information.  Magnification is determined by the size of the eyepiece that is in the telescope, although the amount of magnification is limited by the aperture.  For more information on telescope magnification, see our section on eyepieces.

Telescopes are measured in aperture, not magnification.  Aperture is the diameter of the primary mirror or lens.  The larger the primary mirror or lens, the more light gathering power the telescope.  The more light a telescope can gather, the brighter objects will appear and the more detail you will see.  Also, you can generally achieve more magnification with a greater aperture.

Focal length is another important consideration.  The focal length is the distance from the primary mirror or lens to the focus, or to the eyepiece.  The higher the focal length of the telescope, the greater the magnification will be for any give eyepiece.  Generally, catadioptric telescopes have the greatest focal lengths.

There are also different types of telescope mounts.  Many sold today are motorized mounts.  As the earth rotates, the stars about move from east to west.  If you are viewing an object, it will "move" out of the eyepiece within a few moments.  Many telescopes will track the object so that it is in the eyepiece. Also, many telescope sold today have a GOTO feature.  All you have to do is align the telescope, which is a fairly simple process, and the telescope will point to any one of tens of thousands of objects. 

The most common amateur astronomy telescopes you will see are made by Meade and Celestron.  I have used both brands and they are both of excellent quality.