Optimization of three- and four-element lens systems by minimizing the caustic

Abstract

For an imaging optical system it is, in general, desirable to transform a collection of point sources of light into point images distributed over the focal plane with the appropriate magnification. In practice this is achieved by varying the lens system parameters such that the spread of a bundle of rays from each object point over the image plane has been minimized. A new generalized ray tracing program has been constructed to calculate the principal curvatures of the wavefront associated with a bundle of rays as it passes through an optical system. The caustic surfaces are formed by an optical system and can be determined from the results of the generalized ray tracing program. In this study, the caustic surfaces are used to construct a merit function that describes the spread of the caustic surfaces from an ideal image point. The caustic merit function has been used to optimize a large collection of three- and four-element lenses. The performance of the optimized systems has been evaluated for different field angles by comparing the rms blur circle radii of lenses designed by conventional techniques. Results indicate that minimizing the caustic merit function reduces the rms blur radii over the field of view and the total aberrations of the lens system.