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An optical system includes a diffractive optical element having a diffraction grating provided, on a lens surface having a curvature, in a concentric-circles shape rotationally-symmetrical with respect to an optical axis. The sign of the curvature of the lens surface having the diffraction grating p

An optical system includes a diffractive optical element having a diffraction grating provided, on a lens surface having a curvature, in a concentric-circles shape rotationally-symmetrical with respect to an optical axis. The sign of the curvature of the lens surface having the diffraction grating provided thereon is the same as the sign of a focal length, at a design wavelength, of a system composed of, in the optical system, a surface disposed nearest to an object side to a surface disposed immediately before the lens surface having the diffraction grating provided thereon, and is different from the sign of the distance from the optical axis to a position where the center ray of an off-axial light flux enters the lens surface having the diffraction grating provided thereon. Further, the apex of an imaginary cone formed by extending a non-effective surface of the diffraction grating is located adjacent to the center of curvature of the lens surface having the diffraction grating provided thereon.

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1. 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 the following condition is satisfied:where DL is a distance from (a

1. 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 the following condition is satisfied: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. 2. An optical system according to claim 1, wherein said optical system satisfies the following condition:where D is a distance from the center of curvature of the lens surface having said diffraction grating provided thereon to a focus, 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 provided thereon. 3. An optical system according to claim 2, wherein said optical system satisfies the following condition: 4. An optical system according to claim 1, wherein said optical system satisfies the following condition: 1 ·P<0where P is a refractive power of the lens surface having said diffraction grating provided thereon, and C1 is a phase coefficient for a second-degree term when a phase shape of said diffraction grating is expressed by the following equation: Y )=(2π/λ 0 )( C 1 Y 2 +C 2 Y 4 +C 3 Y 6 + . . . )where Y is the height in a vertical direction from the optical axis, λ 0 is a design wavelength, and C i is a phase coefficient (i=1, 2, 3 . . . ). 5. An optical system according to claim 1, wherein said diffraction grating is a laminated diffraction grating. 6. An optical system according to claim 5, wherein said laminated diffraction grating is an adjacently-laminated diffraction grating in which two diffraction gratings are disposed adjacent to each other across an air layer. 7. An optical system according to claim 6, wherein said adjacently-laminated diffraction grating is provided between two adjacent lens surfaces having substantially the same curvature, and is composed of three layers, including, in order from a front side, a first layer, a second layer and a third layer, said second layer being the air layer. 8. An optical system according to claim 6, wherein each of said two diffraction gratings of said adjacently-laminated diffraction grating are formed with ultraviolet-curable plastic. 9. An optical system according to claim 1, wherein said diffraction grating is a blazed-type diffraction grating. 10. An optical apparatus, comprising:an optical system according to claim 1. 11. An optical apparatus according to claim 10, wherein said optical apparatus is selected from the group of optical apparatuses consisting of an image pickup apparatus, a film camera, a video camera, a digital camera, an observation apparatus, a telescope, a binocular, a projection exposure apparatus, and a stepper for manufacturing a semiconductor device. 12. An optical system according to claim 1, wherein the apex of the imaginary cone is located on the optical axis, andwherein said diffraction grating is entirely a blazed-type diffraction grating.