1. Image formation and aberrations

1.1 Image formation

Figure 1 illustrates image formation in optics. The object is described by a set of elementary sources. Each elementary source emits a wave, assumed to be spherical. The role of the imaging optical system is to transport this set of spherical waves into an image plane, converting diverging spherical waves into converging spherical waves. A diaphragm, or pupil, limits the transverse extent of the waves as they pass through the optical system.