Patent ID: 7336406

Claim:
A scanning optical device comprising: a monolithic multi-laser having a plurality of light-emitting parts; a diaphragm; a light deflector configured to deflect, on the same deflecting surface, all of the plurality of light fluxes emitted from the plurality of light-emitting parts; an incidence optical system disposed in a light path between the monolithic multi-laser and the light deflector, and the incidence optical system being configured to cause all of the plurality of light fluxes emitted from the plurality of light-emitting parts to pass through a same aperture of the diaphragm and being configured to cause the principal rays of all of the plurality of light fluxes to enter the same deflecting surface of the light deflector at different angles in a sub scanning section; a separation optical system configured to direct the plurality of light fluxes deflected on the same deflecting surface of the light deflector into different photosensitive members; an imaging optical system configured to cause the plurality of light fluxes deflected on the same deflecting surface to form images on the different photosensitive members; and a lateral magnification βsi, between the diaphragm and its conjugate point in the sub scanning direction, of an optical system disposed in a light path between the diaphragm and the light deflector, satisfies 1/20<|βsi |<⅓.