Optical element, imaging lens unit, image pickup apparatus

1. An optical unit comprising in order from an object side:

a first optical element and a second optical element,

wherein the first optical element includes:

an effective diameter area that is centered on an optical axis and transmits an effective light beam; and

a flange portion extending substantially perpendicular to a direction of the optical axis and including an image-side flange surface which is perpendicular to the direction of the optical axis, the image-side flange surface having a circumferential recess, extending along at least a portion of a circumference of a circle centered around the optical axis,

wherein a light beam incident on the image-side flange surface is refracted by the circumferential recess towards a light-shielding member disposed between flange portions of the first optical element and the second optical element, and

wherein the circumferential recess has a slope on a sidewall thereof.

2. The optical unit according to claim 1 , wherein the image-side flange surface is provided on a surface of the first optical element which faces an image.

3. The optical unit according to claim 1 , wherein the slope is provided in an inner edge portion or an outer edge portion of the circumferential recess.

4. The optical unit according to claim 3 , wherein the slope is provided in both the inner edge portion and the outer edge portion of the circumferential recess.

5. The optical unit according to claim 4 ,

wherein the slope includes recesses provided in the inner edge portion and the outer edge portion of the circumferential recess, and

wherein an area connecting the recesses in the inner edge portion and the outer edge portion is a flat surface substantially perpendicular to the optical axis.

6. The optical unit according to claim 1 , wherein the slope is provided along the entirety or a part of a circumference of a circle centered on the optical axis on the image-side flange surface.

7. An imaging lens unit comprising in order from an object side:

a first lens having a positive refractive power;

a second lens having a negative refractive power;

a third lens having a positive refractive power; and

a fourth lens having a negative refractive power,

wherein the second lens or the third lens has an effective diameter area that is centered on an optical axis and transmits an effective light beam, and a flange portion extending substantially perpendicular to a direction of the optical axis and including an image-side flange surface which is perpendicular to the direction of the optical axis, the image-side flange surface having a circumferential recess extending along at least a portion of a circumference of a circle centered around the optical axis,

wherein a light beam incident on the image-side flange surface is refracted by the circumferential recess towards a light-shielding member disposed between flange portions of the second lens or the third lens and a lens that is adjacent to the second lens or the third lens on an image-side, and

wherein the circumferential recess has a slope on a sidewall thereof.

8. An imaging lens unit comprising in order from an object side:

a first lens having a positive refractive power;

a second lens having a negative refractive power;

a third lens having a positive refractive power;

a fourth lens having a positive refractive power; and

a fifth lens having a negative refractive power,

wherein the second lens or the third lens has an effective diameter area that is centered on an optical axis and transmits an effective light beam, and a flange portion extending substantially perpendicular to a direction of the optical axis and including an image-side flange surface which is perpendicular to the direction of the optical axis, the image-side flange surface having a circumferential recess extending along at least a portion of a circumference of a circle centered around the optical axis,

wherein a light beam incident on the image-side flange surface is refracted by the circumferential recess towards a light-shielding member disposed between flange portions of the second lens or the third lens and a lens that is adjacent to the second lens or the third lens on an image-side, and

wherein the circumferential recess has a slope on a sidewall thereof.

9. An image pickup apparatus comprising:

an imaging lens unit including, in order from an object side, a first lens having a positive refractive power, a second lens having a negative refractive power, a third lens having a positive refractive power, and a fourth lens having a negative refractive power; and

an image pickup device that converts an optical image formed by the imaging lens unit into an electrical signal,

wherein the second lens or the third lens has an effective diameter area that is centered on an optical axis and transmits an effective light beam, and a flange portion extending substantially perpendicular to a direction of the optical axis and including an image-side flange surface which is perpendicular to the direction of the optical axis, the image-side flange surface having a circumferential recess extending along at least a portion of a circumference of a circle centered around the optical axis,

wherein a light beam incident on the image-side flange surface is refracted by the circumferential recess towards a light-shielding member disposed between flange portions of the second lens or the third lens and a lens that is adjacent to the second lens or the third lens on an image-side, and

wherein the circumferential recess has a slope on a sidewall thereof.

10. The optical unit according to claim 1 , wherein the image-side flange surface further includes a second circumferential recess.

11. The optical unit according to claim 1 , wherein the image-side flange surface further includes at least one projection disposed along at least a portion of the circumference of the circle centered around the optical axis.

12. The image pickup apparatus according to claim 9 , wherein the image-side flange surface is provided on a surface of an optical element which faces an image.

13. The image pickup apparatus according to claim 9 , wherein the slope is provided in an inner edge portion or an outer edge portion of the circumferential recess.

14. The image pickup apparatus according to claim 13 , wherein the slope is provided in both the inner edge portion and the outer edge portion of the circumferential recess.

15. The image pickup apparatus according to claim 14 ,

wherein the slope includes recesses provided in the inner edge portion and the outer edge portion of the circumferential recess, and

wherein an area connecting the recesses in the inner edge portion and the outer edge portion is a flat surface substantially perpendicular to the optical axis.

16. The image pickup apparatus according to claim 9 , wherein the slope is provided along the entirety or a part of a circumference of a circle centered on the optical axis on the side surface of the flange portion.

17. The image pickup apparatus according to claim 9 , wherein the image-side flange surface further includes a second circumferential recess.

18. The image pickup apparatus according to claim 9 , wherein the image-side flange surface further includes at least one projection disposed along at least a portion of the circumference of the circle centered around the optical axis.