Abstract: A multi-beam scanning optical system includes a plurality of light sources, a deflecting unit which deflects a plurality of laser beams emitted from the light sources, and a scanning optical unit which focuses the laser beams deflected by the deflecting unit onto the surface of a photosensitive member. The scanning optical unit is set such that lateral chromatic aberration is overcorrected. In addition, among angles formed between each laser beam incident on the surface of the photosensitive member and the normal at the surface of the photosensitive member in a sub-scanning direction, the oscillation wavelength of the light source that emits a laser beam forming the minimum angle is set to a value smaller than the oscillation wavelength of the light source that emits a laser beam forming the maximum angle.

Abstract: A scanning optical device has a light source, a deflector for deflecting light emitted from the light source, and an optical system for guiding the light emitted from the light source onto a surface to be scanned. The scanning optical device incorporates a mechanism for displacing a refraction section or/and a diffraction section of the optical system. A color image forming apparatus incorporates the scanning optical devices and image carrying members corresponding thereto.

Abstract: A scanning optical device has a first light source unit for generating a plurality of light beams, a second light source unit for generating at least one light beam, and a deflecting scanner for deflecting by a reflecting surface the light beams generated by the first and second light source units to scan a member to be scanned. The positions of the plurality of laser beams generated by the first light source unit are different from each other in a scanning direction in which the deflecting scanner scans, and the at least one light beam generated by the second light source unit is positioned between the plurality of light beams generated by the first light source unit in the scanning direction.