Aberration

In physics, an optical system is said to have an aberration when it does not provide a sharp and accurate image of the object being viewed.

In an optical imaging system, geometrical aberration is a discrepancy between the paraxial radius defined in the Gauss approximation and the corresponding real radius.

A geometrical aberration can also be a discrepancy between the surface of a paraxial wave and the surface of a real wave.

Examples of geometrical aberrations: spherical aberration, coma, astigmatism, field curvature, distortion.