Patent ID: 7570444
Filing Date: 2009-08-04
Classification: G02B

Abstract:
1. An imaging optical system for image reading, in which image information on a surface of an original is imaged on a line sensor and the image information is read by the line sensor, comprising: a first off-axial optical element and a second off-axial optical element disposed in order from an original side, each of the first and second off-axial optical elements is a reflection type off-axial optical element having free-form surface shape and made of a resin material, wherein, letting a main scanning direction be a line direction of the line sensor and a sub-scanning direction be a direction orthogonal to the main scanning direction, a length of each of the first and second off-axial optical elements in the main scanning direction is longer than a length thereof in the sub-scanning direction and a thickness thereof is smaller than the length thereof in the sub-scanning direction, and wherein in a sub-scanning section in which the main scanning direction corresponds to a normal, the following condition is satisfied, where θ a represents an absolute value of a first angle formed between a surface normal to a reflective surface of the first off-axial optical element at a reflection point of the reflective surface of the first off-axial optical element at which a reference axis light beam is reflected and a reference axis light beam incident on the reflective surface of the first off-axial optical element and θb represents an absolute value of a second angle formed between a surface normal to a reflective surface of the second off-axial optical element at a reflection point of the reflective surface of the second off-axial optical element at which the reference axis light beam is reflected and the reference axis light beam incident on the reflective surface of the first off-axial optical element.