Patent attributes
In an lens of a scanner unit, a first incidence surface of a first lens is formed as an aspherical surface rotationally symmetrical with respect to an optical axis while a first emergence surface is formed as a shape asymmetrical in a main scanning direction with respect to the optical axis and having a curvature asymmetrically variable in a sub scanning direction with respect to the optical axis. Each of second incidence surface and second emergence surface of a second lens is formed as a shape symmetrical in the main scanning direction with respect to the optical axis and having a curvature symmetrically variable in the sub scanning direction with respect to the optical axis. A mold for the lens can be produced easily when only the first emergence surface of the first lens can be formed as an asymmetrically variable shape.
