Patent ID: 6956685

Claim:
A method of detecting a synchronizing beam for controlling optical write-in starting of each beam for scanning each scanning line in a multi-beam scanner, the method comprising the steps of: deflecting each of beams emitted from a plurality of light sources and modulated independently according to an image signal by a common deflector at an equiangular velocity toward a scanned surface, and converging the deflected beam toward the scanned surface by a scanning image-forming optical system including lenses so as to be formed into a plurality of light spots on the scanned surface, separated from each other in a sub-scanning direction, to simultaneously scan a plurality of scanning lines by use of the plurality of light spots; and sequentially guiding each deflected beam by a synchronizing beam optical system of a synchronization detecting system toward a light receiving device of the synchronization detecting system so as beam, the synchronization detecting system reducing the value of a parameter d 1 /ω 1 , where d 1 is a maximum shift in a beam position in a main scanning direction at a light receiving face position of the light receiving device, caused by a difference in inter-beam wavelength in a synchronizing beam detecting view angle, and ω 1 is a beam displacement at the light receiving face position corresponding to a unit change in a view angle of the synchronizing beam detecting view angle.