Imaging element and image reading apparatus
First Claim
Patent Images
1. An imaging element comprising:
- a diffraction optical element on which off-axis beams with field angles are incident;
a stop; and
a limiting member located at a position farther away from said diffraction optical element than said stop, wherein said diffraction optical element has a grating surface with grating facets, each of said grating facets having a continuous surface inclined at a blaze angle or having a binary approximation of a nominal surface inclined at a blaze angle, each of said grating facets having a respective facet normal defined as being perpendicular to the respective surface inclined at a blaze angle, wherein, of off-axis beams incident on said diffraction optical element and having field angles, beam portions incident on at least one of said grating facets at incident angles larger than the incident angle of the principal ray of the beam of which said portions are a part are partially shielded by said limiting member, and wherein the incident angle of a beam portion incident on given grating facet is an angle defined by said beam portion and the normal to the surface of said given grating facet.
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Abstract
An imaging element includes a diffraction optical element on which an off-axis beam with a field angle is incident and a stop. Of beams having different field angles and incident on the diffraction optical element, beams having incident angles larger than the incident angle of a principal light ray of the beams incident on the grating surface of the diffraction optical element are partially shielded by a light-shielding member, so that the diffraction efficiencies of orders adjacent to a design order are kept low and hence imaging performance almost free from flare can be achieved even if a beam with a field angle is incident.
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Citations
19 Claims
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1. An imaging element comprising:
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a diffraction optical element on which off-axis beams with field angles are incident;
a stop; and
a limiting member located at a position farther away from said diffraction optical element than said stop, wherein said diffraction optical element has a grating surface with grating facets, each of said grating facets having a continuous surface inclined at a blaze angle or having a binary approximation of a nominal surface inclined at a blaze angle, each of said grating facets having a respective facet normal defined as being perpendicular to the respective surface inclined at a blaze angle, wherein, of off-axis beams incident on said diffraction optical element and having field angles, beam portions incident on at least one of said grating facets at incident angles larger than the incident angle of the principal ray of the beam of which said portions are a part are partially shielded by said limiting member, and wherein the incident angle of a beam portion incident on given grating facet is an angle defined by said beam portion and the normal to the surface of said given grating facet. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 19)
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17. An imaging element comprising:
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a diffraction optical element on which off-axis beams with field angles are incident;
a stop; and
a limiting member located at a position farther away from said diffraction optical element than said stop, wherein said diffraction optical element has a grating surface with grating facets, each of said grating facets having a continuous surface inclined at a blaze angle or having a binary approximation of a nominal surface inclined at a blaze angle, each of said grating facets having a respective facet normal defined as being perpendicular to the respective surface inclined at a blaze angle, wherein, of off-axis beams incident on said diffraction optical element and having field angles, beam portions incident on at least one of said grating facets at incident angles larger than the incident angle of the principal ray of the beam of which said portions are a part are partially shielded by said limiting member, with the incident angle of a beam portion incident on given grating facet being an angle defined by said beam portion and the normal to the surface of said given grating facet, wherein said limiting member is disposed on an incident and/or exit side of said imaging element, wherein said limiting member comprises a second stop, and wherein, when D is a diameter of said stop, f is a focal length of said imaging element, Y is a maximum object height, and β
is an absolute value of an imaging magnification, a distance L from said stop to said second stop serving as the exit-side light-shielding member along the optical axis falls within a range;
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18. An imaging element comprising:
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a diffraction optical element on which off-axis beams with field angles are incident;
a stop; and
a limiting member located at a position farther away from said diffraction optical element than said stop, wherein said diffraction optical element has a grating surface with grating facets, each of said grating facets having a continuous surface inclined at a blaze angle or having a binary approximation of a nominal surface inclined at a blaze angle, each of said grating facets having a respective facet normal defined as being perpendicular to the respective surface inclined at a blaze angle, wherein, of off-axis beams incident on said diffraction optical element and having field angles, beam portions incident on at least one of said grating facets at incident angles larger than the incident angle of the principal ray of the beam of which said portions are a part are partially shielded by said limiting member, with the incident angle of a beam portion incident on given grating facet being an angle defined by said beam portion and the normal to the surface of said given grating facet, wherein said limiting member is disposed on an incident and/or exit side of said imaging element, wherein said limiting member comprises a second stop, and wherein, when D is a diameter of said stop, f is a focal length of said imaging element, Y is a maximum object height, and β
is an absolute value of an imaging magnification, a distance L from said stop to said second stop serving as the incident-side light-shielding member along the optical axis falls within a range;
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Specification