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Types of research astronomical telescopes vary by the optics used to magnify and direct the EMR, and by the portion of the electromagnetic spectrum they observe. Telescopes also vary by the sensors and instruments they use to collect data, but often include a choice of sensors/instruments and common telescope classification terms are most often not based upon the sensors. Some classification terms refer to the telescope's purpose.
The telescope's EMR spectral band gives rise to terms such as radio telescope, X-ray telescope, etc. The optics is generally either refractive (using lenses or the equivalent, a refracting telescope) or reflective (using mirrors or equivalent reflectors, a reflector telescope). Many of the terms refer to the arrangements or shapes of mirrors or other reflectors, some of the terms which are applicable to and used for radio telescopes as well as UV, optical, and infrared telescopes:
Off-axis telescope is a general class, inherent in some of these types and optionally incorporated in some others.
The Wolter telescope design is specifically aimed at X-rays and gamma rays, using only incident optics, i.e., such that all its reflections modify the ray-direction over small angles.
There are also telescope classification terms based on various other characteristics, design elements and/or purposes:
This page is oriented toward sizable research telescopes. Among small telescopes, e.g., amateur telescopes, additional designs are common, often aimed at attaining their capabilities within a feasible price range or with feasible at-home construction effort. Such smaller telescopes are used by interested amateurs for research purposes, and are also sometimes used by professional astronomers for some specific types of projects.