A refracting or refractor telescope is a dioptric telescope that uses a lens as its objective to form an image. The refracting telescope design was originally used in spy glasses and astronomical telescopes but is also used in other devices such as binoculars and long or telephoto camera lenses.

Reflecting Telescope

A reflecting telescope (reflector) is an optical telescope which uses a combination of curved or plane (flat) mirrors to reflect light and form an image (catoptric), rather than lenses to refract or bend light to form an image (dioptric).

Catadioptric Telescope

A catadioptric optical system is one which contains both lenses and mirrors. Catadioptric systems are commonly used in telescopes and in lightweight, long-focus lenses for cameras.