TABLE OF CONTENTS This chapter is written as a discussion of illuminating systems, based on the concept that we want to efficiently produce some level of uniform illumination from a given source. In almost every case, however, one can substitute a detector for the source and reverse the direction of the light, and the result is an analogous "radiometer" system of comparable efficiency. After Sec. 3.2 it is left to the reader to make this substitution.
The usual requirement for an illuminating system is to produce a uniform illumination from a nonuniform light source, such as a lamp filament or an arc. Koehler illumination is the classical way of achieving this. As shown in Fig. 3.1, a condenser images the source in the pupil of the projection lens. The projection lens images the region of the condenser on the area to be illuminated. The illumination produced is the same as if a magnified source, located at the projection lens, were directly illuminating the target area. For a given projection lens diameter, the maximum illumination is produced when the lens pupil is filled by the image of the source. As indicated in Fig. 3.1, a simple spherical reflector centered on the source will image the source back on itself, increasing the average brightness of the source and thus increasing the illumination on the target area. Condenser elements often have a molded aspheric surface; this can reduce or eliminate the spherical...
