A
reflecting telescope (also called a
reflector) is an
optical telescope which uses a single or combination of
curved mirrors that reflect
light and form an
image. The reflecting telescope was invented in the 17th century as an alternative to the
refracting telescope which, at that time, was a design that suffered from severe
chromatic aberration. Although reflecting telescopes produce other types of optical aberrations, it is a design that allows for very large diameter
objectives. Almost all of the major telescopes used in
astronomy research are reflectors. Reflecting telescopes come in many design variations and may employ extra optical elements to improve image quality or place the image in a mechanically advantageous position. Since reflecting telescopes use
mirrors, the design is sometimes referred to as a "
catoptric" telescope.