Patent ID: 7990572

Claim:
An image forming apparatus including N latent image carriers (N denoting a natural number of N≧2) each formed with a linear latent image on its surface by scanning a single light beam thereon along a main scan direction, the apparatus comprising: a light source for emitting a single light beam; and optical scan means operative to deflect the light beam from said light source for scanning along said main scan direction and to guide said scanned beam along a subscan direction different from said main scan direction, thereby selectively switching the light beam to any one of said N latent image carriers for irradiation with said scanned beam, wherein said optical scan means comprises: an inner movable member having a deflector mirror plane for reflecting the light beam from said light source; an outer movable member for pivotally supporting said inner movable member about a first axis; a support member for pivotally supporting said outer movable member about a second axis different from said first axis; and a mirror driver section for driving said inner movable member into pivotal motion about said first axis and said outer movable member into pivotal motion about said second axis, wherein said mirror driver section drives said deflector mirror plane into pivotal motion about a main-scan deflection axis defined by either one of said first axis and said second axis thereby scanning the light beam from said light source along said main scan direction, and also drives said deflector mirror plane into pivotal motion about a switch axis defined by the other axis thereby selectively switching said scanned beam to any one of the latent image carriers for irradiation with said scanned beam, wherein the apparatus further comprises a third optical system for focusing the light beam, scanned by said deflector mirror plane along said main scan direction, on the latent image carrier to which the scanned beam is guided by said deflector mirror plane, and wherein said third optical system comprises a single lens and has a distortion characteristic that the scanned beam deflected based on a swinging characteristic intrinsic to said deflector mirror plane is moved on the surface of each latent image carrier at a constant speed, the third optical system specified that opposite sides in a tangential plane are formed in mutually different non-arcuate shapes in a manner to correct for tangential field-curvature aberration in the light beam at any position on the surface of each latent image carrier, and that sagital curvatures at positions on the non-arcuate curve of at least either one of said opposite sides in the tangential plane are varied non-correlatively of the tangential curvature in order to correct for sagital field-curvature aberration in the light beam.