Design and tolerancing of achromatic and anastigmatic diffractive–refractive lens systems compared with equivalent conventional lens systems

Abstract

Since focal diffractive optics have been introduced, designing them has flourished, particularly as the manufacturing technology has developed to meet the performance requirements. My purpose is to introduce to hybrid diffractive-refractive optical systems not only the design procedure but also the optical and the mechanical aspects of optical tolerancing. A comparison is made with equivalent conventional (purely refractive) systems in the visible wave band (rather than the infrared wave band where there are many published designs) to seek advantages and disadvantages that systems with diffractive optics bring. The results of tolerancing comparisons show that for small-field systems the introduction of diffractive components has a powerful desensitizing effect, whereas for a wide-field anastigmatic system that has been investigated the desensitization effect of the inclusion of diffractive surfaces is less marked. These results come mainly from the fact that an achromatizing diffractive surface has little focal power, whereas an achromatizing refractive component has to have a large focal power.