Focus detecting optical system

摘要

A focus detecting optical system for detecting a focus condition of an image of an object to be picked-up by an image forming lens including a condenser lens arranged in a vicinity of a predetermined focal plane of the image forming lens, aperture stop having a plurality of apertures, a plurality of image reforming lenses and a plurality of light receiving element arrays. At least one diffractive optical element having a lens function due to a diffraction is provided on a surface of the condenser lens or image reforming lenses. The diffractive optical element may be formed by kinoform or binary optical element having a step-wise configuration. The diffractive optical element may be formed in a surface of an infrared cut filter.