A reflecting telescope which has a mirror at its base with a central hole: The Cassegrain telescope is constructed to allow light reflected from this primary mirror to pass through it after being reflected by a convex secondary mirror.

A space-based astronomical observing facility, orgiting the earth at an altitude of 610 kilometers/380 miles.

It is constructed of a 2.4 meter/94 inch telescope and four complimentary scientific instruments, which are roughly cylindrical, 13 meters/43 feet long, and four meters/13 feet in diameter, with two large solar panels.

An instrument used to make observations of celestial bodies at radio wavelengths: The radio telescope usually consists of an aerial which collects the radiation and feeds it to a processing computer.

A telescope that uses lenses to gather light from faint objects: The front objective lens of the refractor telescope is usually made of two or more components, with the eyepiece at the other end being the point at which the observer sees the image of the object.

1. A camera mounted in a Schmidt telescope: A Schmidt camera is a telescope-camera able to take pictures covering a wide area of the sky without optical problems by virtue of having a specially shaped corrector plate near its upper-end.
2. A wide-angle photographic telescope used in astronomy which has a special internal mirror to correct optical aberrations: A Schmidt telescope is a type of reflecting telescope; more accurately, a large camera, in which the coma produced by a spherical concave mirror is compensated for by a thin correcting lens placed at the opening of the telescope tube and has a usable field of 0°.6.

The Schmidt telescope has a corrector lens that prevents distortions of the image which is produced by its large spherical mirror.

Something called "spherical aberration" occurs when the uncorrected mirror does not focus all of the light rays at the same point.