(1) The condition whereby objects in a plane perpendicular to the optical axis are imaged in a curved or dish shaped surface. Equivalently, an aberration affecting the longitudinal position of images off the axis so that objects in a plane perpendicular to the axis are imaged on a curved surface. Some telescopes used in astronomy and geodesy have pronounced curvature of field. This is particularly true of Schmidt telescopes, in which the focal surface is spherical and photographic film must be cut in the form of a Maltese cross in order to lie flat on the surface. (2) The distance, parallel to the optical axis, from an off axis image point to the plane through an on axis image point and perpendicular to the optical axis.