Patent ID: 7397620
Filing Date: 2008-07-08
Classification: G02B

Abstract:
1. 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, r are used, then conditions expressed by are satisfied, where A on and B on are values of the constants A and B concerning a principal ray of abaxial light, respectively, and A off and B off are values of the constants A and B concerning a principal ray of most abaxial light, respectively.