Patent ID: 7889426

Claim:
A scanning lens for an imaging optical system that converges a beam emitted by a light source and deflected by a deflector on a target surface to form a beam spot scanning in a main scanning direction thereon, the scanning lens including a plastic lens formed by injection molding, the plastic lens having a diffractive lens structure formed by the injection molding on at least one surface thereof, the diffractive lens structure having a plurality of concentric annular zones which are arranged concentrically about a rotational axis, each of the plurality of annular zones having a diffracting surface that diffracts the light beam passing therethrough, the diffractive lens structure having stepped surfaces connecting each adjoining diffracting surfaces, the stepped surfaces being designed such that, in a plane including the rotational axis and parallel with the main scanning direction, the stepped surfaces are inclined with respect to the rotational axis so that stress working between a metallic molding for the plastic lens and each of the stepped surfaces in demolding is reduced.