Optical scanning device, line-image forming optical system therein, imaging adjustment method in the device and image forming apparatus

An optical scanning device comprising:

• a light source emitting a light flux;
• a coupling optical system coupling the light flux from said light source to a subsequent optical system by transforming the light flux into one of a parallel light flux, an approximately convergent light flux, and an approximately divergent light flux;
• a light deflector reflecting the light flux from said coupling optical system with a deflection reflective surface, and deflecting the light flux;
• a scanning and imaging optical system condensing the deflected light flux from said light deflector onto a surface to be scanned as a beam spot;
• and
• a correcting optical system, disposed between said coupling optical system and the deflection reflective surface, for performing a self correcting shift of focal position of the beam spot on said surface to be scanned,
• wherein said correcting optical system comprises at least one pair of lenses comprising a resin-made lens having an anamorphic surface with a negative power in each of a main scanning direction and a sub-scanning direction, and a glass-made lens having an anamorphic surface with a positive power in at least the sub-scanning direction.