Patent ID: 7016114

Claim:
An imaging optical system comprising: an iris stop; a layered diffraction optical member laminated with a plurality of diffraction parts, wherein said layered diffraction optical member is provided in front of said iris stop; and a refraction optical member disposed on a rear side of said iris stop, wherein said layered diffraction optical member includes a first diffraction part of negative power and a second diffraction part of positive power provided behind said first diffraction part, wherein said first diffraction part and said second diffraction part each include a diffraction grating, and said diffraction grating of said first diffraction part is made of a material having a dispersion characteristic different from that of a material from which said diffraction grating of said second diffraction part is made, wherein said layered diffraction optical member is formed to have high diffraction efficiency for diffracted light of a particular order over a visible wavelength range to be used in said imaging optical system, wherein said imaging optical system forms an image on an image plane with light that has passed through said layered diffraction optical member, said iris stop, and said refraction optical member, and wherein said layered diffraction optical member further comprises a positive meniscus lens and a positive biconvex lens, with said first diffraction part being disposed on said positive meniscus lens and said second diffraction part being disposed on said positive biconvex lens.