Patent ID: 6825979
Filing Date: 2004-11-30
Classification: G02B

Abstract:
An optical system, comprising:a diffractive optical element having a diffraction grating provided, on a lens surface having curvature, in a concentric-circles shape rotationally-symmetrical with respect to an optical axis, wherein a sign of the curvature of the lens surface having said diffraction grating provided thereon is the same as a sign of a focal length, in a design wavelength, of a system composed of, in said optical system, a surface disposed nearest to a front side to a surface disposed immediately before the lens surface having said diffraction grating thereon, and is different from a sign of a distance from the optical axis to a position where a center ray of an off-axial light flux enters the lens surface having said diffraction grating provided thereon, wherein the following condition is satisfied: |DL/R|<0.3 where DL is a distance from (a) the apex of an imaginary cone formed by extending a non-effective surface of said diffraction grating to (b) the center of curvature of the lens surface having said diffraction grating provided thereon, and R is a radius of curvature of the lens surface having said diffraction grating provided thereon.