Telescopes bring the night sky into focus.
Telescopes magnify light so stars and other astronomical bodies, previously unseen by the naked eye, can be observed. Two basic types of telescopes exist: refracting and reflecting. Refracting telescopes bend light to create an image, while reflecting telescopes use a mirror as the objective lens to reflect light. The objective lens, or mirror, serves several functions for the reflecting telescope.
Collection of Light
A reflecting telescope collects light; more light means greater magnification. Increase the diameter of the objective lens or mirror, and you collect more light. The ability to magnify light from stars is really the ability to collect more light, which allows faint stars to appear brighter. The telescope works on the same principle as the human eye. Enter a dark room and you cannot see at first, but then as your eyes adjust you regain vision. The increase in vision results from your pupil enlarging, which enables more light to enter your eye.
Reflection
Light enters a reflecting telescope, and the objective lens, or mirror, reflects the light. The first reflecting telescope was designed by Sir Isaac Newton and is called the Newtonian reflecting telescope. In this telescope, the function of the objective lens is to reflect light to another smaller mirror, which is flat. That small mirror in turn reflects the light to the eyepiece, where an image appears.
Size
Reflecting telescopes contain objective lens up to 8 meters, or just over 26 feet in diameter. This large size serves the function of the reflecting telescope, which is increased magnification. Combine smaller mirrors and the size increases up to 10 meters, or almost 33 feet.
Types
The function of the objective lens or mirror varies depending upon the type of reflecting telescope. While the Newtonian uses the mirror to reflect light to a flat mirror, the prime focus reflecting telescope reflects light directly to a camera or other device without the use of a second mirror. The prime focus works for cameras and very large telescopes. The Cassegrain reflecting telescope uses include large instruments like photometers and spectographs. It employs a hyperbolic second mirror with a magnification factor that allows for a shorter telescope with the same power.
Tags: objective lens, reflecting telescope, lens mirror, more light, objective lens mirror
