Imaging lens and image reading apparatus using it

• US 6,507,444 B2
• Filed: 09/24/1999
• Issued: 01/14/2003
• Est. Priority Date: 10/02/1998
• Status: Expired due to Term

• Current Assignee: Canon Ayutthaya Limited (Canon Inc.)
• Original Assignee: Canon Ayutthaya Limited (Canon Inc.)
• Inventors: Hayashide, Tadao, Kondo, Kazuyuki
• Primary Examiner(s): Epps, Georgia
• Assistant Examiner(s): THOMPSON, TIMOTHY J
• Application Number:
  US09/404,760
• Publication Number:
  US 20020163739A1
• Time in Patent Office: 1,208 Days
• Field of Search: 359/720, 359/631, 359/633, 359/729, 359/364, 359/365, 359/366, 359/727, 359/724
• US Class Current: 359/720
• CPC Class Codes: G02B 13/24 for reproducing or copying at short object distances

Abstract

An imaging lens is used in image reading and adapted to image information of an original on a reading device. In the imaging lens at least one surface out of a plurality of surfaces forming the imaging lens has refracting power rotationally asymmetric with respect to the optical axis.

Claims

1. An imaging lens for use in image reading, for imaging image information of an original on a linear image sensor,

wherein said imaging lens is formed of a plurality of surfaces having a common optical axis, and

wherein at least one surface out of said plurality of surfaces has a refracting power rotationally asymmetric with respect to the optical axis so as to diminish aberrations arising from a predetermined angle of view formed between an off-axis principal ray and an on-axis principal ray which are reflected by said original.

2. The imaging lens according to claim 1, wherein said surface having the rotationally asymmetric refracting power is a surface of a rotationally asymmetric shape and is integral with a surface of a single lens forming said imaging lens.

3. The imaging lens according to claim 1, wherein said surface having the rotationally asymmetric refracting power is a diffracting optical element having rotationally asymmetric refracting power and is integral with a surface of a single lens forming said imaging lens.

4. The imaging lens according to claim 1, wherein said surface having the rotationally asymmetric refracting power is formed by adding a member of a rotationally asymmetric shape with respect to the optical axis to a rotationally symmetric surface.

5. The imaging lens according to claim 1, wherein said surface having the rotationally asymmetric refracting power is formed by adding a diffracting optical element having refracting power rotationally asymmetric with respect to the optical axis, to a rotationally symmetric surface.

6. The imaging lens according to any one of claims 1 to 5, said imaging lens being used in an image reading apparatus adapted to image the image information of the original illuminated by light from an illumination light source on a surface of the reading means and read the image information.

42. The imaging lens according to claim 1, wherein the radius of curvature in the direction of the generating line varies with distance from the optical axis along the direction of the generating line.

44. The imaging lens according to claim 1, wherein the radius of curvature in the direction of the meridian line varies with distance from the optical axis along the direction of the generating line.

46. An imaging reading apparatus comprising:

an image reader configured to read an image, said image reader comprising;

reading means for reading image information; and

an imaging lens configured to imaging image information on said reading means, according to any of claims 1, 3-5, 7, 9, 10, 12, 17, 23, 29, and 37.

47. The imaging lens according to claim 1, wherein said surface having the rotationally asymmetric refracting power is a surface a radius of curvature of a generating line of which is equal to a radius of curvature of a meridian line thereof on the optical axis.

7. An imaging lens for use in image reading, for imaging image information of an original on reading means, said imaging lens having a stop in the imaging lens,

wherein at least one surface not facing said stop, out of a plurality of surfaces forming the imaging lens, has a refracting power rotationally asymmetric with respect to the optical axis,

wherein said plurality of surfaces have a common optical axis.

8. The imaging lens according to claim 7, wherein said surface having the rotationally asymmetric refracting power is a surface of a rotationally asymmetric shape having rotationally symmetric refracting power on the optical axis and is integral with a surface of a single lens forming said imaging lens.

43. The imaging lens according to claim 7, wherein the radius of curvature in the direction of the generating line varies with distance from the optical axis along the direction of the generating line.

45. The imaging lens according to claim 7, wherein the radius of curvature in the direction of the meridian line varies with distance from the optical axis along the direction of the generating line.

48. The imaging lens according to claim 7, wherein said surface having the rotationally asymmetric refracting power is a surface a radius of curvature of a generating line of which is equal to a radius of curvature of a meridian line thereof on the optical axis.

49. The imaging lens according to claim 7, wherein said reading means is a linear image sensor.

9. The imaging lens for use in image reading, for imaging image information of an original on reading means,

said imaging lens having a stop in the imaging lens,

wherein at least one surface not facing said stop, out of a plurality of surfaces forming the imaging lens, has a refracting power rotationally asymmetric with respect to the optical axis,

wherein said surface having the rotationally asymmetric refracting power is a surface a radius of curvature of a generating line of which is equal to a radius of curvature of a meridian line thereof on the optical axis.

39. The imaging lens according to claim 9, wherein the radius of curvature in the direction of the generating line varies with distance from the optical axis along the direction of the generating line.

41. The imaging lens according to claim 9, wherein the radius of curvature in the direction of the meridian line varies with distance from the optical axis along the direction of the generating line.

10. The imaging lens for use in image reading, for imaging image information of an original on reading means,

said imaging lens having a stop in the imaging lens,

wherein at least one surface not facing said stop, out of a plurality of surfaces forming the imaging lens, has a refracting power rotationally asymmetric with respect to the optical axis,

wherein said surface having the rotationally asymmetric refracting power is formed by adding a member of a rotationally asymmetric shape with respect to the optical axis to a rotationally symmetric surface.

11. The imaging lens according to any one of claims 7 to 10, said imaging lens being used in an image reading apparatus adapted to image the image information of the original illuminated by light from an illumination light source on a surface of the reading means and read the image information.

12. An imaging lens for use in image reading, for imaging image information of an original on reading means, wherein at least one surface at which an overlapping area of a range of up to 70% of a distance from a center to the outermost periphery of each of on-axis rays and outermost off-axis rays is not more than 50% of an area of a range of up to 70% of the distance from the center to the outermost periphery of the on-axis rays, out of a plurality of surfaces forming the imaging lens, has refracting power rotationally asymmetric with respect to the optical axis.

13. The imaging lens according to claim 12, wherein said surface having the rotationally asymmetric refracting power is a surface of a rotationally asymmetric shape having rotationally symmetric refracting power on the optical axis and is integral with a surface of a single lens forming said imaging lens.

14. The imaging lens according to claim 13, wherein said surface having the rotationally asymmetric refracting power is a surface a radius of curvature of a generating line of which is equal to a radius of curvature of a meridian line thereof on the optical axis.

15. The imaging lens according to claim 12, wherein said surface having the rotationally asymmetric refracting power is formed by adding a member of a rotationally asymmetric shape with respect to the optical axis to a rotationally symmetric surface.

16. The imaging lens according to any one of claims 12 to 15, said imaging lens being used in an image reading apparatus adapted to image the image information of the original illuminated by light from an illumination light source on a surface of the reading means and read the image information.

17. An imaging lens for use in image reading, for imaging image information of an original on reading means, said imaging lens comprising five lenses, which are a positive, first lens of the meniscus shape with a convex surface thereof facing the side of the original, a second lens whose lens surfaces both are concave surfaces, a third lens whose lens surfaces both are convex surfaces, a positive or negative, fourth lens of a meniscus shape with a convex surface thereof facing the side of the reading means, and a negative, fifth lens of the meniscus shape with a convex surface thereof facing the side of the reading means, arranged in the named order from the original side,

wherein at least one surface out of a plurality of surfaces forming the imaging lens has refracting power rotationally asymmetric with respect to the optical axis.

18. The imaging lens according to claim 17, wherein said surface having the rotationally asymmetric refracting power is a surface of a rotationally asymmetric shape having rotationally symmetric refracting power on the optical axis and is integral with a surface of a single lens forming said imaging lens.

19. The imaging lens according to claim 18, wherein said surface having the rotationally asymmetric refracting power is a surface a radius of curvature of a generating line of which is equal to a radius of curvature of a meridian line thereof on the optical axis.

20. The imaging lens according to claim 17, wherein said surface having the rotationally asymmetric refracting power is formed by adding a member of a rotationally asymmetric shape with respect to the optical axis to a rotationally symmetric surface.

21. The imaging lens according to claim 17, further comprising a stop between said second lens and said third lens.

22. The imaging lens according to any one of claims 17 to 21, said imaging lens being used in an image reading apparatus adapted to image the image information of the original illuminated by light from an illumination light source on a surface of the reading means and read the image information.

50. The imaging lens according to claim 17, wherein said reading means is a linear image sensor.

23. An imaging lens for use in image reading, for imaging image information of an original on reading means, said imaging lens comprising four lenses, which are a positive, first lens of the meniscus shape with a convex surface thereof facing the side of the original, a second lens whose lens surfaces both are concave surfaces, a third lens whose lens surfaces both are convex surfaces, and a negative, fourth lens of the meniscus shape with a convex surface thereof facing the side of the reading means, arranged in the named order from the original side,

wherein at least one surface out of a plurality of surfaces forming the imaging lens has refracting power rotationally asymmetric with respect to the optical axis.

24. The imaging lens according to claim 23, wherein said surface having the rotationally asymmetric refracting power is a surface of a rotationally asymmetric shape having rotationally symmetric refracting power on the optical axis and is integral with a surface of a single lens forming said imaging lens.

25. The imaging lens according to claim 24, wherein said surface having the rotationally asymmetric refracting power is a surface a radius of curvature of a generating line of which is equal to a radius of curvature of a meridian line thereof on the optical axis.

26. The imaging lens according to claim 23, wherein said surface having the rotationally asymmetric refracting power is formed by adding a member of a rotationally asymmetric shape with respect to the optical axis to a rotationally symmetric surface.

27. The imaging lens according to claim 23, further comprising a stop between said second lens and said third lens.

28. The imaging lens according to any one of claims 23 to 27, said imaging lens being used in an image reading apparatus adapted to image the image information of the original illuminated by light from an illumination light source on a surface of the reading means and read the image information.

51. The imaging lens according to claim 23, wherein said reading means is a linear image sensor.

29. An imaging lens for use in image reading for imaging image information of an original on reading means, wherein at least one surface out of a plurality of surfaces forming the imaging lens has refracting power rotationally asymmetric with respect to the optical axis,

wherein in such a coordinate system that an origin lies at an intersecting point of said one surface with the optical axis, x along a direction of the optical axis, y along a reading direction of the reading means, and z along a direction perpendicular to the optical-axis direction x and to the reading direction y,

letting R(y) be a radius of local curvature at a certain point in said reading direction y on an xy section of said one surface, and r(y) be a radius of local curvature in a direction perpendicular to the xy plane and normal to the shape of the xy section in the reading direction y,

the following condition is satisfied in a range of the reading direction y from 0 to a passing position y′

of an outermost off-axis principal ray;

30. The imaging lens according to claim 29, wherein said R(y) satisfies the following condition in the range of the reading direction y from 0 to the passing position y′

of the outermost off-axis principal ray;

31. The imaging lens according to claim 29 or 30, wherein said R(y) and said r(y) are equal to each other on the optical axis.

32. The imaging lens according to claim 29, wherein said surface having the rotationally asymmetric refracting power is a surface of a rotationally asymmetric shape and is integral with a surface of a single lens forming said imaging lens.

33. The imaging lens according to claim 29, wherein said surface having the rotationally asymmetric refracting power is formed by adding a member of a rotationally asymmetric shape with respect to the optical axis to a rotationally symmetric surface.

34. The imaging lens according to claim 29, wherein said reading means is a linear image sensor.

35. The imaging lens according to any one of claims 29, 30, and 32 through 34, said imaging lens being used in an image reading apparatus adapted to image the image information of the original illuminated by light from an illumination light source on a surface of the reading means and read the image information.

36. The imaging lens according to claim 31, said imaging lens being used in an image reading apparatus adapted to image the image information of the original illuminated by light from an illumination light source on a surface of the reading means and read the image information.

37. An imaging lens for use in image reading, for imaging image information of an original on reading means,

wherein at least one surface out of a plurality of surfaces forming the imaging lens has a refracting power rotationally asymmetric with respect to the optical axis,

wherein said surface having the rotationally asymmetric refracting power is a surface a radius of curvature of a generating line of which is equal to a radius of curvature of a meridian line thereof on the optical axis.

38. The imaging lens according to claim 37, wherein the radius of curvature in the direction of the generating line varies with distance from the optical axis along the direction of the generating line.

40. The imaging lens according to claim 37, wherein the radius of curvature in the direction of the meridian line varies with distance from the optical axis along the direction of the generating line.

52. An image reading apparatus for reading image information of an original, comprising a linear image sensor arranged in a main scanning direction and an imaging lens for imaging image information of an original on said linear image sensor, said original and said linear image sensor being scanned in a sub scanning direction relatively to each other,

wherein said imaging lens is formed of a plurality of surfaces having a common optical axis, and

wherein at least one surface out of said plurality of surfaces has a refracting power rotationally asymmetric with respect to the optical axis so as to diminish aberrations arising from a predetermined angle of view formed between an off-axis principal ray and an on-axis principal ray which are reflected by said original.

53. An image reading apparatus according to claim 52, wherein said at least one surface has radii of curvature in generating and meridian line directions which are different from each other at any position of the surface.

54. An image reading apparatus according to claim 52, wherein said at least one surface has radii of curvature in the generating and meridian line directions which are equal to each other only on the optical axis.

55. An image reading apparatus according to claim 52, wherein said at least one surface has a radius of curvature in a generating line direction which varies continuously from the on-axis position toward the outermost off-axis position.

56. An image reading apparatus according to claim 52, wherein said at least one surface has a radius of curvature in a meridian line direction which varies continuously from the on-axis position toward the outermost off-axis position.

57. An image reading apparatus for reading image information of an original, comprising a linear image sensor arranged in a main scanning direction and an imaging lens for imaging image information of an original on said linear image sensor, said original and said linear image sensor being scanned in a sub scanning direction relatively to each other,

wherein said imaging lens is formed of a plurality of surfaces having a common optical axis and includes a stop, and

wherein at least one surface not facing said stop, out of said plurality of surfaces, has a refracting power rotationally asymmetric with respect to the optical axis.

58. An image reading apparatus according to claim 57, wherein said at least one surface has radii of curvature in generating and meridian line directions which are different from each other at any position of the surface.

59. An image reading apparatus according to claim 57, wherein said at least one surface has radii of curvature in the generating and meridian line directions which are equal to each other only on the optical axis.

60. An image reading apparatus according to claim 57, wherein said at least one surface has a radius of curvature in a generating line direction which varies continuously from the on-axis position toward the outermost off-axis position.

61. An image reading apparatus according to claim 57, wherein said at least one surface has a radius of curvature in a meridian line direction which varies continuously from the on-axis position toward the outermost off-axis position.

62. An image reading apparatus for reading image information of an object, comprising an image sensor and an imaging lens for imaging image information of an object on said image sensor,

wherein said imaging lens is formed of a plurality of surfaces having a common optical axis, and

wherein at least one surface out of said plurality of surfaces has a refracting power rotationally asymmetric with respect to the optical axis so as to diminish aberrations arising from a predetermined angle of view formed between an off-axis principal ray and an on-axis principal ray which are reflected by said original.

63. An image reading apparatus according to claim 62, wherein said at least one surface has radii of curvature in generating and meridian line directions which are different from each other at any position of the surface.

64. An image reading apparatus according to claim 62, wherein said at least one surface has radii of curvature in generating and meridian line directions which are equal to each other only on the optical axis.

65. An image reading apparatus according to claim 62, wherein said at least one surface has a radius of curvature in a generating line direction which varies continuously from the on-axis position toward the outermost off-axis position.

66. An image reading apparatus according to claim 62, wherein said at least one surface has a radius of curvature in a meridian line direction which varies continuously from the on-axis position toward the outermost off-axis position.

67. An image reading apparatus for reading image information of an object, comprising an image sensor and an imaging lens for imaging image information of an object on said image sensor,

wherein said imaging lens is formed of a plurality of surfaces having a common optical axis and includes a stop, and

wherein at least one surface not facing said stop, out of said plurality of surfaces, has a refracting power rotationally asymmetric with respect to the optical axis.

68. An image reading apparatus according to claim 67, wherein said at least one surface has radii of curvature in generating and meridian line directions which are different from each other at any position of the surface.

69. An image reading apparatus according to claim 67, wherein said at least one surface has radii of curvature in the generating and meridian line directions which are equal to each other only on the optical axis.

70. An image reading apparatus according to claim 67, wherein said at least one surface has a radius of curvature in a generating line direction which varies continuously from the on-axis position toward the outermost off-axis position.

71. An image reading apparatus according to claim 67, wherein said at least one surface has a radius of curvature in a meridian line direction which varies continuously from the on-axis position toward the outermost off-axis position.