Aberration

In Chapter 1 on Geometrical Optics we discussed geometrical image formation by using paraxial theory. The essential assumption of paraxial theory is that the angles between an emerging ray from the object and the axis of the system are small. In general small means that one could replace sin α by the angle α (in radians). When this assumption can not be made, one obtains a distorted image. There are elaborate computational programs available for lens design, including systematic corrections for the various types of aberrations. To give an introduction to the most commonly known monochromatic aberrations, we discuss spherical aberration of a single refracting surface and a thin lens, and coma, and astigmatism of a spherical surface and a thin lens. At the end we also discuss chromatic aberration.