Shining Some Starlight on the Refracting Telescope

Although Galileo has historically been credited with the invention of the refracting telescope in the early 1600s, credit should be given to three eye doctors whose work helped him develop the theory of refraction for his telescope. Refracting telescopes are very simple and have only two main components — a convex lens called the objective lens, and a concave lens that makes up the eyepiece.

The convex lens is located at the end of the telescope and serves to refract or bend the light that enters the telescope and turn it into a single beam of light. Then the image you are looking at shows up in reverse on the concave lens, which turns the image around. Refraction telescopes allow the viewer to see very bright and clear images.

The refracting telescope invented by Galileo is used today by many people but the drawback is the small field of view it offers. A well known refracting telescope is the one in California at the Chabot Space and Science Center. The center actually has two refracting telescopes — an eight-inch refracting telescope and a 21-inch refracting telescope. They are very basic telescopes and therefore spherical aberrations can occur. One way these aberrations are dealt with is by using a pair of lenses (a convex and a flat lens) to create an achromatic lens.

Refracting Telescopes and Color

One of the most common issues with a refracting telescope is the separation of light that occurs when the light is bent. When this happens, it is called chromatic aberration and it can be remedied with the use of an achromatic lens.

One problem with large refracting telescopes is getting the lens large enough without any imperfections that will be picked up as light goes through the lens. There are 41-inch lenses but they are unusable. Refracting telescopes are generally not used by professional astronomers due to the issue of getting all the light to focus in on one place at the same time.

Refracting telescopes are popular among novice astronomers and are utilized at observatories around the world. It is a good telescope choice for beginners due to the lens being enclosed that makes the image appear to be less shaky and have less movement than reflecting telescopes, which send the image to the viewer’s eye from a mirror. The process of reflecting light from the first mirror to the second and then the eye piece can cause an unsteady image.