Definition

An aberration affecting the sharpness of IMAGES off the AXIS, in which RAYS from a point object off the AXIS passing through a given circular zone of the LENS, come to a FOCUS in a circle rather than a point, and the circles formed by RAYS through different zones are of different sizes and are located at different distances from the AXIS. Therefore, the IMAGE of a point object is comet-shaped. The foggy envelope surrounding the nucleus of a COMET.