Abstract: A multi-beam scanning optical system is provided with a plurality of laser diodes respectively emitting a plurality of laser beams, each of said plurality of laser diodes being accommodated in a casing, and a laser diode holding unit that holds the casings of the plurality of laser diodes. Heat generated by each of the plurality of laser diodes is conducted to each other through the casings of the plurality of laser diodes and the laser diode holding unit.

Abstract: A multi-beam scanning optical system is provided with a light source unit, polygonal mirror, and an f&thgr; lens. The f&thgr; lens includes first, second and third lenses. The beams emitted by the light source unit are incident on the first, second and third lenses in this order. The first lens consists of two lens elements, the first lens element converges the plurality of beams in an auxiliary scanning direction. The second lens element converges the plurality of beams in a main scanning direction. A plurality of convex surfaces, which correspond to the plurality of beams and converge the plurality of beams in the auxiliary scanning direction, respectively, are formed on one of surfaces of the first and second lens elements. Further, a diffraction lens structure for compensating for lateral chromatic aberration caused by a refraction lens structure of the f&thgr; lens system is formed on each of the plurality of convex surfaces.

Abstract: A multi-beam scanning optical system is provided with a light source unit, polygonal mirror, and an f&thgr; lens. The f&thgr; lens includes a first lens that converges the beams mainly in the main scanning direction, and a second lens that converges the beams mainly in the auxiliary scanning direction. The first and second lenses are made of different materials. Further, one of the first and second lenses is formed integrally with the other using a mold such that the first and second lenses constitute a composite lens unit.

Abstract: A multi-beam scanning optical system is provided with a light source unit emitting a plurality of beams. The beams are incident on a polygonal mirror, and deflected thereby to scan in a predetermined scanning range. The scanning beam is incident an f&thgr; lens system. The f&thgr; lens system includes a plurality of lenses, and all the beams pass at least one of the plurality of lenses included in the f&thgr; lens system. The lens, which all the beams pass through, is formed as a single lens element made of single material. Further, the lens contributes to convergence of the beams in the main scanning direction.

Abstract: A multi-beam scanning device is provided with a light source that emits a plurality of light beams, a polygonal mirror that deflects the light beams to scan, and an optical system that converges the deflected light beams on a plurality of objects to be scanned. The objects are arranged on a side, with respect to the polygonal mirror, in which the light beams scan, from a position closer to the polygonal mirror to a position farther from the polygonal mirror in order. The optical system further includes a plurality of optical path turning systems that turn optical paths of the deflected light beams, respectively. Each of the optical path turning systems includes a plurality of reflection surfaces, the numbers of the reflection surfaces of the optical path turning systems are all even, or odd.