Optical scanning apparatus, image forming apparatus, and methods of performing optical scanning using optical scanning apparatus and image forming apparatus

A method for performing optical scanning using an optical scanning apparatus including a laser unit in which a light source and collimator lens are integrated, an incident optical system for making a light beam emerging from the laser unit strike an optical deflector while keeping the light beam wider than a width of a deflecting surface of the optical deflector in a main scanning direction, and an imaging optical system for forming the light beam reflected/deflected by the optical deflector into an image on a scanned surface, comprising the step of:

• shifting the laser unit in a predetermined direction with respect to the optical axis of the incident optical system so as to make an illuminance distribution of scanning lines on the scanned surface become substantially symmetrical about a scanning central axis.

A method for performing optical scanning using an optical scanning apparatus including a laser unit having a laser source and an optical element configured to emit a substantially parallel beam of light, an incident optical system arranged to direct the light beam emerging from the laser unit to strike an optical deflector while maintaining a width of the light beam wider than a width of a deflecting surface of the optical deflector in a main scanning direction, and an imaging optical system for forming the light beam deflected by the optical deflector into an image on a scanned surface, the method comprising the step of:

• moving the laser unit in the main scanning direction without changing a direction of an optical axis of the incident optical system so as to make an illuminance distribution of scanning lines on the scanned surfae become substantially symmetrical about a scanning central axis.