Annular lens design for reducing spherical aberration

According to the relationship between the image distance and parameter of refraction surface,the refraction surface is divided into several concentric annulus between which exist certain distance along the optical axis.As a ray of parallel light incident,the different annulus of refraction surface making image position of incident ray overlap to reduce spherical aberration.According to the content mentioned above a lens with two annulus designed and then the aberration analyzed by CODEV.In compared with doublet lens:The spherical aberration、wave front aberration and the spot diagram of the lens are declined Further more MTF become better which are close to diffraction limit.