ABSTRACT
Spherical aberration is the most important of all primary aberrations, because it affects the whole field of a lens, including the vicinity of the optical axis (Toraldo Di Francia, 1953). The name of this aberration comes from the fact that it is observed in most spherical surfaces, refracting or reflecting. The aberration is due to the different focus positions for marginal meridional and paraxial rays, as shown in Fig. 4.1. The value of this aberration may be calculated by means of many different methods.
