Lens fault in which light rays are scattered, thereby degrading the image. There are different forms of aberration, such as chromatic and spherical aberration, coma, astigmatism and field curvature.
Aberrations can be a great problem in optical printing and projection.
Failure of a lens to bring light of different wavelengths to a common focus. This can be compensated by using an achromatic lens.
Failure of a lens system to image the central and peripheral rays at the same focal point.