Lens array, lens unit, LED head, exposure unit, image formation apparatus, and reading apparatus

1. A lens array comprising:

arranged lenses, wherein

each of at least two adjacent lenses in the lens array includes:

a first region located at and around an optical axis of the lens and having a first curvature;

a second region located farther away from the optical axis than the first region and having a second curvature, and

a third region provided between the first region and the second region, the third region connecting the first region and the second to each other, and the third region having a third curvature different from the first and second curvatures,

the second curvature is larger than the first curvature.

2. The lens array according to claim 1 , wherein

the third curvature is smaller than the first curvature.

3. The lens array according to claim 1 , wherein the second region is a crosstalk prevention portion.

4. The lens array according to claim 3 , wherein

the optical axes of the lenses are parallel to one another,

the lenses are arranged with the optical axes thereof placed in parallel to one another and with no appreciable gap interposed therebetween in a direction perpendicular to the optical axes of the lenses, and

the crosstalk prevention portions are located at outer peripheral portions of the lenses.

5. The lens array according to claim 4 , wherein the crosstalk prevention portions are formed only at two end portions in a neighborhood of the lenses in a direction perpendicular to a longitudinal direction in which the arranged lenses are formed as a lens plate.

6. An LED head comprising the lens array according to claim 1 .

7. An image formation apparatus comprising the lens array according to claim 1 .

8. A reading apparatus comprising the lens array according to claim 1 .

9. The lens array of claim 1 , wherein

each of 70 percent or more of the arranged lenses in the lens array includes:

the first region located at and around the optical axis of the lens and having the first curvature; and

the second region located farther away from the optical axis than the first region and having the second curvature, the second curvature being larger than the first curvature.

10. A lens unit comprising:

lens arrays; and

a light-shield member provided between the lens arrays, wherein

each of the lens arrays includes arranged lenses,

each of at least two adjacent lenses in the lens array includes:

a first region located at and around an optical axis and having a first curvature;

a second region located farther away from the optical axis than the first region and having a second curvature, and

a third region provided between the first region and the second region, the third region connecting the first region and the second to each other, and the third region having a third curvature different from the first and second curvatures,

the second curvature is larger than the first curvature.

11. The lens unit according to claim 10 , wherein

the light-shield member comprises:

an aperture configured to transmit a light ray passing through each of the lenses in the lens array; and

a light-shield portion configured to block a light ray passing through the second region of one of the lenses adjacent to the lens.

12. The lens unit according to claim 11 , wherein

the lens arrays comprise a first lens array and a second lens array,

the first lens array forms a reduced inverted image of an object, and

the second lens array forms a same-size erect image of the object by forming an enlarged inverted image of the reduced inverted image.

13. An LED head comprising the lens unit according to claim 10 .

14. The lens unit according to claim 10 , wherein the third curvature is smaller than the first curvature.

15. The lens unit according to claim 10 , wherein the second region is a crosstalk prevention portion.

16. The lens unit according to claim 15 , wherein

the optical axes of the lenses are parallel to one another,

the lenses are arranged with the optical axes thereof placed in parallel to one another and with no appreciable gap interposed therebetween in a direction perpendicular to the optical axes of the lenses, and

the crosstalk prevention portions are located at outer peripheral portions of the lenses.

17. The lens unit according to claim 16 , wherein the crosstalk prevention portions are formed only at two end portions in a neighborhood of the lenses in a direction perpendicular to a longitudinal direction in which the arranged lenses are formed as a lens plate.