Telescope Reviews

Choosing a Refracting Telescope, Reflecting Telescope or Catadiotric Telescope

February 8th, 2007 Subscribe To Our Feed

From back in the days of the Renaissance, the telescope was invented and built by spectacle makers. It wasn’t until some time later that the famous Galileo made some remarkable improvements that were the basis for today’s modern telescopes. The various telescope types are broken down into three categories: a refracting telescope, a reflecting telescope and a catadiotric telescope.

How Does a Telescope Work?

The way the majority of telescopes work is by focusing light that passes into the telescope. When you look in the eyepiece of a telescope, what you see is actually a larger image. This is the result of the telescope making the light converge; basically concentrating the light it receives in order to make things appear larger or brighter. There are several different telescope types, and while the design in each is a little different, each of the telescope types does the same basic job of focusing light.

The Grandfather of Telescopes - The Refracting Telescope

The first of the telescope types created was the refracting telescope. This telescope makes use of precisely ground lenses to focus the light. These telescopes use the glass of the lenses to bend light, such as in a prism, in order to bring the light to focus. This basic design is the principle behind binoculars, which are essentially two refracting telescopes that are attached, and telephoto lenses for cameras. This design isn’t without problems, though.

If the telescope is designed badly, it can focus different colors of light improperly, resulting in a blurring effect called chromatic aberration. Similarly, spherical aberration, imperfection due to the curved lenses used in telescopes, also creates blurred images. Refracting telescopes are not often used in large research telescopes now, because at the large sizes needed, gravity makes the glass lenses sag and creates further distortion.

A Refracting and Reflecting Telescope - What’s the Difference?

A reflecting telescope accomplishes the same thing as refracting telescope. Though, as the name implies, it’s through using curved mirrors to reflect the light rather than lenses to pass through it. While attempts were made to create reflecting telescopes about the same time as the first refracting telescopes were being put to use, it wasn’t until a few decades later that a working model was developed.

It was Sir Isaac Newton that managed the first working reflecting telescope, and in his honor, the Newtonian Telescope bears his name. Reflecting telescope types are favored by designers of large, research-grade telescopes, since big mirrors can be supported on the back, which helps prevent the sagging that happens with large lenses, which can only be supported around their edge. Some reflecting telescopes do suffer from spherical aberration as well as coma, an effect in which stars that aren’t in the center of the field of view will appear wedge-shaped rather than as points of light.

Catadioptric Telescopes - A Combined Refracting and Reflecting Telescope Design

The last of the optical telescope types are catadioptric telescopes. These use a combined design of the best features of both the refracting and reflecting telescope. The Catadioptric telescope tends to correct most of the aberration problems of other telescope designs. However, as a drawback, they are often designed with a secondary mirror in the center of the tube, which blocks a little of the light that comes into the telescope. Because some designs of catadioptric telescopes are easily made and powerful for their size, they are often popular with manufacturers seeking to reach a mass market. These telescope types, however, are not used much as research telescopes, where reflecting telescopes are still the most popular.

The interesting point is that although the Catadioptric telescope is provided its own unique category, it is essentially just a hybrid of the other the refracting and reflecting telescope. This fact is really just a testament to the brilliant design of the original telescopes.

Regardless of which telescope type you choose, you will know that you are benefiting from a design that was invented centuries ago. Of course with today’s technology, computer enhancement and setting options have only added to the functionality and usefulness of these engineering marvels.