Telescope Fun

The telescope is an invention that dates back to Renaissance times, originally built by spectacle makers and improved by Galileo. The way most telescopes work is by focusing light that passes into the telescope. Though when you look in the eyepiece of a telescope, what you see is a larger image, this is actually a 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.

Refracting Telescopes

The first of the telescope types created was the refracting telescope, which 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.

Reflecting Telescopes

A reflecting telescope accomplishes the same thing as reflecting 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 around the time that the first refracting telescopes were being put to use, it wasn’t until a few decades after that Isaac Newton managed the first working model, and in his honor, one of the reflecting telescope types, 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

The last of the optical telescope types are catadioptric telescopes, which combine refraction and reflection. These tend to correct most of the aberration problems of other telescope designs, though 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 in research telescopes, where reflecting telescopes are still the most popular.

And though it’s given its own category, they are essentially just a combination of the other two telescope types. It is a testament to the simple, solid design of the telescope that the best improvement that can be made is to combine the best features of the other two telescope types. But no matter which type you choose to use, you will find yourself benefiting from the usefulness of this invention from centuries past.