| US 7,612,941 B2 | ||
| Diffractive optical element and optical system including the same | ||
| Takehiko Nakai, Utsunomiya (Japan) | ||
| Assigned to Canon Kabuhsiki Kaisha, Tokyo (Japan) | ||
| Filed on Sep. 04, 2007, as Appl. No. 11/849,971. | ||
| Application 11/849971 is a continuation of application No. 11/093085, filed on Mar. 29, 2005, granted, now 7,301,702. | ||
| Claims priority of application No. 2004-109091 (JP), filed on Apr. 01, 2004. | ||
| Prior Publication US 2007/0297057 A1, Dec. 27, 2007 | ||
| This patent is subject to a terminal disclaimer. | ||
| Int. Cl. G02B 5/18 (2006.01) | ||
| U.S. Cl. 359—576 [359/570] | 1 Claim |
| 1. An optical system comprising:
a diffractive optical element including a plurality of diffraction gratings laminated and being composed of at least two materials
having different dispersions; and
a refractive optical element,
wherein at least one of the diffraction gratings includes a plurality of grating parts having a curved grating surface and
grating tips that connect to define a curved envelope face,
wherein the grating surface has a radius of curvature larger than a radius of curvature of the envelope face,
wherein an absolute value of the radius of curvature of the envelope face is between one-fifteenth of a focal length of the
optical system to one-half of the focal length of the optical system, inclusive,
wherein the grating parts of the diffraction grating are arranged concentrically with respect to each other, and the grating
side of the grating part is substantially parallel to an optical axis of the optical system, and
wherein the plurality of diffraction gratings are bonded together at an area where the grating parts are not formed.
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