Telescopes

Telescopes come in three major classification: refractors, reflectors, and catadioptrics. Refractors use lenses to gather light, while reflectors use mirrors to gather light. Catadioptric telescopes contain a combination of lenses and mirrors. Refractors with single-lens objectives suffer severely from chromatic aberration. Doublet objectives, sometimes called acromats, use two lenses to reduce some of the chromatic aberration. Using three or more lenses in the objective essentially eliminates all chromatic aberration. These refractors are known as apochromats. Popular styles of reflectors include Newtonians, Cassegrains, Ritchey–Chrétien Cassegrains, and Dall-Kirkham Cassegrains. Each has its own unique optical design. The most popular catadioptric telescope is the Schmidt-Cassegrain. Other catadioptric designs include Maksutov-Cassegrains, Maksutov Newtonians, and Corrected Dall-Kirkhams. Three important properties of telescope, in order of importance, are light-gathering power, resolution, and magnification. Eyepieces are used to transfer the light from a telescope onto an image visible to the human eye. The quality of a telescope eyepiece is just as important as the telescope itself to produce a pleasing image of a celestial object.