What does the curved mirror on a telescope do?

Answer 1

The mirror in a telescope is a concave mirror. That shape redirects all the light coming from a distant object that hits the mirror into a focusing lens. The mirror may be as small as several inches or many feet in diameter and it concentrates the light so it can be focused by a small eyepiece that may be only a fraction of an inch in diameter. The mirror serves the same purpose as a large lens in a refractive telescope. It takes a large cross section of light and focuses it into the eyepiece of the telescope but it does it by reflection rather than refraction. The reflective mirror is preferred over a lens for several reasons. The light reflected by a good quality silvered mirror loses very little of its intensity. Light passing through a lens loses intensity each time it passes through a glass surface and it must pass through 2 surfaces of a lens. The mirror bends the light one time and a lens bends it twice. The more times you bend light, the more chance you have to introduce distortion because of imperfections of the surface. If the glass of a lens is not ultra pure and without imperfection, the light is further distorted. The quality of glass in a mirror does not affect the light because the light does not pass through the mirror because the light is reflected off the first surface. When very large telescopes are involved, a refraction lens would weigh many times what the reflective mirror weighs.