Patent ID: 8681406

Claim:
A multibeam scanning optical apparatus comprising: a light source unit for emitting a plurality of light beams; a light deflector for deflecting and reflecting the light beams; and an imaging optical system for imaging the light beams deflected by said light deflector on a surface to be scanned, wherein said imaging optical system has a plurality of lens surfaces, wherein the light beams are incident on said imaging optical system at positions which are different in a sub-scanning direction, and curvatures of the lens surfaces in the sub-scanning direction change continuously, independently of the curvatures in a main-scanning direction and non-symmetrically with respect to the optical axis of the imaging optical system along the main-scanning direction so that Fmin/Fmax≧0.9 is satisfied, where Fmax is a maximum value of a F number of the light beam incident on the surface to be scanned with respect to the sub-scanning direction, and Fmin is a minimum value of a F number of the light beam incident on the surface to be scanned with respect to the sub-scanning direction, and wherein said imaging optical system comprises a single lens.