Optical scanning device and image forming apparatus

An optical scanning device comprising:

• a light source that emits a light beam;
• a deflector having a deflection surface that deflects the light beam;
• and
• a first lens and a second lens that are arranged on an optical path of the light beam deflected by the deflector, the first and second lenses extending in a main scanning direction and a sub-scanning direction of the light beam, the light beam passing through the first and second lenses in this order,
• wherein
• the light source is arranged at a position where the light beam strikes the deflection surface obliquely in the sub-scanning direction,
• for the first and second lenses, shapes of entrance and exit surfaces thereof with respect to the light beam are defined by a main scanning direction shape formula and a sub-scanning direction shape formula that include different coefficients for one side and another side with respect to a middle in the main scanning direction,
• the sub-scanning direction shape formula includes, as a variable, a sub-scanning direction curvature radius defined by a sub-scanning direction curvature radius definition formula, and
• the sub-scanning direction curvature radius definition formula is given by a polynomial with a coordinate in the main scanning direction as a variable, and includes a first order term of the variable.