Image reading apparatus using image reading lens

An image reading apparatus, comprising:

• a photoelectric conversion element having picture elements arrayed in a main-scan direction;
• and
• an image reading lens for imaging imagewise information on a surface of an original, upon a light receiving surface of said photoelectric conversion element,
• wherein said image reading lens includes at least one anamorphic lens having anamorphic surfaces formed at a light entrance surface and a light exist surface thereof, respectively,
• wherein, when a sectional shape of the anamorphic surface in a main-scan section which contains an optical axis of said image reading lens and the main-scan direction, is taken as a meridional, a curvature of a sagittal of the anamorphic surface defined within a plane being perpendicular to the main-scan section and containing a normal to the anamorphic surface at an arbitrary position in the meridional direction, changes continuously along the meridional direction from the optical axis,
• wherein, when N is a refractive index of a material of the anamorphic lens, rin is a curvature radius of the sagittal at a position where a principal ray passes through the light entrance surface of the anamorphic lens, rout is a curvature radius of the sagittal in a direction perpendicular to the main-scan section and at a position where the principal ray passes through the light exit surface of the anamorphic lens, d is a distance in the optical axis direction between the positions where the principal ray passes the light entrance surface and the light exit surface of the anamorphic lens, respectively, ω is a largest half field angle of said image reading lens, and when constants A and B expressed by
• A
• =
• N
• -
• 1
• r
• i
• ⁢
• ⁢
• n
• ⁢
• (
• 1
• -
• 1
• r
• out
• ⁢
• (
• r
• i
• ⁢
• ⁢
• n
• -
• d
• ⁡
• (
• N
• -
• 1
• )
• N
• )
• )
• B
• =
• 1
• -
• d
• ⁡
• (
• N
• -
• 1
• )
• N
• ⁢
• ⁢
• r
• i
• ⁢
• ⁢
• n
• are used, then conditions expressed by
• 0.8
• <
• A
• off
• A
• on
• ⁢
• cos
• ⁢
• ⁢
• ω
• <
• 1.2
• 
• 1
• -
• A
• off
• A
• on
• ⁢
• cos
• ⁢
• ⁢
• ω
• 
• +
• 
• 1
• -
• B
• off
• B
• on
• ⁢
• cos
• ⁢
• ⁢
• ω
• 
• <
• 0.2
• are satisfied, where Aon and Bon are values of the constants A and B concerning a principal ray of abaxial light, respectively, and Aoff and Boff are values of the constants A and B concerning a principal ray of most abaxial light, respectively.