Refracting telescopes, reflector telescopes and catadioptric telescopes

Before you even turn a yellow page or click on ebay, there are some important things to know about telescopes.

There are three basic categories of telescopes: refractor, reflector, and catadioptric or combination of the first two.

A refracting telescope is the classic telescope image. It has two lenses — the larger objective lens which is at one end gathers the light, focuses it into an image that is magnified and viewed by the eyepiece (ocular) at the other end. On a refracting telescope you can move the eyepiece in and out to get the proper focus. Both lenses are sealed inside the telescope with very little maintenance and offer steady and sharp images. There may be defects in the lenses, that however, can cause blurring, and the size of the lenses are not limitless.

A reflector telescope operates with mirrors and was invented by Isaac Newton. A concave mirror (or Primary) gathers the light, focusing it with another mirror and sending it on to the eyepiece. These reflector telescopes can get very large for better viewing. However, they can become misaligned and can get very dirty, impeding your view. A 4.5" or 6" reflector can be a great choice for a beginning astronomer

A catadioptric telescope (better known as Schmidt-Cassegrain, Maksutov-Cassegrain or other Cassegrain derivatives) takes the best of the previous types, with a secondary mirror bouncing light through the primary mirror to an eyepiece. They are more compact than the refractor and reflector scopes with an ability to hook up to your computer. They are cheaper than the refractor telescope, but more expensive than the reflector and are moisture sensitive.