1. 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.
3. 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.