The reflector telescope uses a mirror to gather and focus light. Because the light rays are parallel to each other, the reflector telescope's mirror has a parabolic shape. The parabolic-shaped mirror focusses the parallel lights rays to a single point. All modern research telescopes and large amateur ones are of the reflector type because of its advantages over the refractor telescope. Advantages Reflector telescopes do not suffer from chromatic aberration because all wavelengths will reflect off the mirror in the same way.
Reflector telescopes are cheaper to make than refractors of the same size.
Because light is reflecting off the objective, rather than passing through it, only one side of the reflector telescope's objective needs to be perfect. Despite the advantages of the reflector telescope, astronomers must contend with some minor annoyances. It is easy to get their optics out of alignment. A reflector telescope's tube is open to the outside and the optics need frequent cleaning. Often a secondary mirror is used to redirect the light into a more convenient viewing spot.