A telescope used at extreme ultraviolet and X-ray wavelengths, for which a conventional mirror is very inefficient because it absorbs photons. In a grazing-incidence telescope, incoming light is reflected off the mirror surface at very shallow angles. Several designs of grazing-incidence telescope have been used in satellites, including flat mirrors or combinations of parabolic and hyperbolic surfaces. To increase the collecting area a number of mirror elements are often nested inside one another.