Patent ID: 8848270

Claim:
An imaging optical system which is used for an image reading apparatus for reading image information of an original by respectively moving the original and a reading unit including multiple reading pixels arranged in a first direction, in a second direction orthogonal to the first direction, and images the original on the reading unit, the imaging optical system comprising an anamorphic lens having an anamorphic surface with an aspherical shape which is rotationally asymmetric about an optical axis, wherein: the anamorphic surface has a non-arc shape in each of a first section orthogonal to the second direction and a second section orthogonal to the first direction; and the anamorphic lens has a positive optical power in the first section on the optical axis, and a non-arc amount in a second section of the anamorphic surface continuously varies with increasing distance from the optical axis along the first direction, so that a Modulation Transfer Function curve does not have a local minimum value over an entire region in the first direction.