Patent ID: 7006120

Claim:
A multi-beam optical scanning apparatus comprising: a semiconductor laser array slanted relative to a sub-scanning direction and emitting a plurality of optical beams; a coupling lens converting a shape of each optical beam emitted from the semiconductor laser array; and an aperture with an opening having a size of A m ×A s , arranged after the coupling lens in a direction in which the optical beam progesses, wherein A m is a dimension of the opening in a main scanning direction and A s is a dimension of the opening in the sub-scanning direction; wherein when a length in the main scanning direction of a contour line defined by 1/e 2 strength of a maximum strength of an optical beam at a position of the aperture is L m ; and a length in the sub-scanning direction of the contour line defined by 1/e 2 strength of the maximum strength of the optical beam at the position of the aperture is L s , following conditional expressions are satisfied: A m <L m ; and L s /L m ×0.3 <A s /A m <L m ×1.7; wherein the multi-beam optical scanning apparatus further comprises: an optical deflector deflecting the optical beam in the main scanning direction; and an image forming optical system arranged after the optical deflector in a direction in which the optical beam progresses and condensing the optical beam to obtain an optical spot having a size of ω m ×ω s on a scanning surface, wherein ω m is a dimension of the optical spot in the main scanning direction and ω s is a dimension of the optical spot in the sub-scanning direction, wherein when a size of an effective area of a surface of the optical deflector is D m ×D s , D m being a dimension of the effective area in the main scanning direction and D s being a dimension of the effective area in the sub-scanning direction; a distance in the main scanning direction between optical beams of the plurality of optical beams reaching the optical deflector, that are separated at most in the main scanning direction, is δ; and an effective writing width on the scanning surface is W, a following conditional expression is satisfied: ( D m ×ω m )/(δ× W )>5×10 −4 .