APPARATUS FOR COMPUTING DIFFRACTION EFFICIENCY OF DIFFRACTION LENS LENS HAVING DIFFRACTIVE ELEMENTS ATTACHED THERETO AND OPTICAL IMAGE READING SYSTEM

摘要

PURPOSE: A lens having a grating element is provided to prevent degradation of diffraction efficiency by specifying an m-th pitch of a rising/ falling shape, counting from the center of the lens. CONSTITUTION: When the focal length of a grating element is fg and center wavelength at the time of forming the grating element is lambda 0 it is so constituted that an m-th pitch Pm of a rising/falling shape, counting from the lens center satisfies an expression. In this case, it is desirable that a grating element face in a lens with the grating element is of kinoform and that the lens is formed of either glass or resin. It is further desirable that the lens with the grating element is formed of infrared absorbing material. As a result, the grating element face is easily formed, and degradation of diffraction efficiency is prevented so as to suppress such an influence that unnecessary scattered light is projected on an image face to degrade image focusing performance.