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

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. In this study, caustic surfaces are used to construct a merit function that describes the spread of the caustic surfaces from an ideal image point. This caustic merit function has been used to optimize a large collection of three- and four-element lens systems. The performance of the optimized lenses has been evaluated by comparing the rms blur circle radii vs field angle to that of similar lenses designed by conventional techniques. The average rms improvement has been calculated for optimized systems. 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 systems, particularly for systems with large apertures and wide fields of view.