TABLE OF CONTENTS In previous chapters and in appendix A we discuss the means by which ray paths are traced through an optical system and how the numerical values of the image aberrations may be determined. In this chapter, we will consider the interpretation of the results of such computations. The basic question to which we address ourselves is: "What effect does a given amount of aberration have on the performance of the optical system?"
We have seen that raytracing yields an incomplete picture of the image-forming characteristics of a system, since the image formed by a "perfect" lens or mirror is not the geometric point that raytracing might lead us to expect, but a finite-sized diffraction pattern the Airy disk and the surrounding rings. For modest departures from perfection (i.e., aberrations which cause a deformation of the wave front amounting to less than one or two wavelengths) it is thus appropriate to consider the manner in which an aberration affects the distribution of energy in the diffraction pattern. For larger amounts of aberration, however, the illumination distribution as described by raytracing can yield a quite adequate representation of the performance of the system. Thus, it is convenient to divide our considerations into (1) the effects of small amounts of aberration, which we treat in terms of the wave nature of light, and (2) the effects of large amounts of aberration, which may be treated geometrically.
We will begin our discussion of small amounts of aberration...
