Diffractive multi-focal objective lens

摘要

A diffractive multi-focal objective lens formed, macroscopically, as a double convex lens having convex aspherical surfaces of which radii of curvatures are larger as a function of distance from the optical axis. One lens surface is provided with a microscopic diffractive lens construction that is formed as ring zones concentric about the optical axis. The diffractive lens construction is designed so that the higher the diffractive order, the shorter the focal length. For example, a first order diffractive light beam forms a first focal point F1 on the optical axis, and a second order diffractive light beam forms a second focal point F2 on the optical axis that is nearer to the lens than the first focal point F1.