Optical element, imaging optical system, and camera module
An optical element incorporated into an imaging optical system, comprising: an effective diameter area that allows effective light flux contributing to imaging to pass, a non-effective diameter area that surrounds the effective diameter area; and an outer peripheral face that surrounds the non-effective diameter area. The effective diameter area, the non-effective diameter area and the outer peripheral face are centered on an imaging optical axis. At least a thickness-direction part of the outer peripheral face or a circumferential part thereof is a non-parallel face having an inclination to an imaging optical axis. A light incident from a face of an object side, reflected on a face of an image-plane side to the outer peripheral face and reflected on the outer peripheral face is not incident to an image plane.
1. An optical element incorporated into an imaging optical system, comprising:
an effective diameter area that allows effective light flux contributing to imaging to pass;
a non-effective diameter area that surrounds the effective diameter area; and
an outer peripheral face that surrounds the non-effective diameter area,
wherein the effective diameter area, the non-effective diameter area and the outer peripheral face are centered on an imaging optical axis,
at least a thickness-direction part of the outer peripheral face or a circumferential part thereof is a non-parallel face being inclined with respect to the imaging optical axis so that the outer diameter of the optical element at the non-parallel face gradually increases toward an image-plane side, and
a light incident from a face of an object side, reflected on a face of the image-plane side to the outer peripheral face and reflected on the outer peripheral face is not incident to an image plane,
wherein the optical element is incorporated with a plurality of lenses into the imaging optical system.
2. The optical element according to claim 1 ,
wherein the non-parallel face is formed with a width equal to or less than ⅔ of the outer peripheral face in the thickness direction, and
the whole or a part of the other outer peripheral face has a cylindrical shape centered on the imaging optical axis.
3. The optical element according to claim 1 ,
wherein the non-parallel face is a curved face represented by a curved line having an inclination continuously changing with respect to a longitudinal cross section including the imaging optical axis.
4. The optical element according to claim 1 ,
wherein the optical element is a formed article made by integrally forming the effective diameter area and the non-effective diameter area including the outer peripheral face.
5. The optical element according to claim 1 ,
wherein the optical element is a lens used at the second or thereafter from the object side in the imaging optical system that includes at least two lenses, and
the optical element has a concave surface on the object side in the effective diameter area directed to the object side.
6. The optical element according to claim 5 ,
wherein the optical element has a convex surface and a concave surface surrounding the convex surface, said concave surface and said convex surface being on the image-plane side in the effective diameter area directed to the image-plane side.
7. The optical element according to claim 5 ,
wherein the optical element is disposed closer to the image-plane side than a stop, and
an effective diameter area on the image-plane side is wider than the effective diameter area on the object side.
8. An imaging optical system comprising, in order from an object side:
a stop;
a first lens;
a second lens; and
a third lens,
wherein any one of the second lens and the third lens is the optical element according to claim 5 .
9. A camera module comprising:
a lens unit that is formed by incorporating the imaging optical system according to claim 8 into a lens barrel; and
an imagining unit that is fixed to a rear end of the lens barrel and keeps a solid state imaging element so that the imaging face coincides with the image plane.
10. The optical element according to claim 1 ,
wherein the outer peripheral face has a changing point located at a point equal to or less than ⅔ of the width of the outer peripheral face in the thickness direction, and
the non-parallel face has said inclination such that the outer diameter of the optical element gradually increases from said changing point toward the image-plane side.
11. An optical element incorporated into an imaging optical system, comprising:
an effective diameter area that allows effective light flux contributing to imaging to pass;
a non-effective diameter area that surrounds the effective diameter area; and
an outer peripheral face that surrounds the non-effective diameter area,
wherein the effective diameter area, the non-effective diameter area and the outer peripheral face are centered on an imaging optical axis,
the optical element is formed of a multi-color formed article having a circular-ring-shaped boundary face of the non-effective diameter area,
at least a thickness-direction part of the boundary face or a circumferential part thereof is a non-parallel face having an inclination to an imaging optical axis,
a part of the outer peripheral face is a cylindrical face centered on the imaging optical axis, and
an undesirable light incident from the effective diameter area of a face of an object side, internally reflected on the effective diameter area of a face of an image-plane side toward the boundary face, and internally and specularly reflected on the boundary face is internally and totally reflected on the face of the object side or the image-plane side.