Patent ID: 6940535

Claim:
A multi-beam optical scanning device comprising: light source means having a plurality of light emitting points spaced apart at least in a main scanning direction; deflection means for deflecting a plurality of light beams emitted from the light source means; a scanning optical system for focusing the plurality of light beams deflected by the deflection means on a surface to be scanned; and synchronous detection means for detecting timing at which the plurality of light beams start scanning in an effective scanning area on the surface to be scanned, wherein a width in the main scanning direction of each of the plurality of light beams incident on the deflection means is wider than the width in the main scanning direction of an area of movement of a deflection facet of the deflection means for which the deflection facet is effective to deflect the plurality of light beams emitted from the light source means toward the entire effective scanning area on the surface to be scanned and toward the synchronous detection means provided outside the effective scanning area, and wherein, when an angle defined in the main scanning direction by principal rays of the plurality of light beams emitted from the light source means when the plurality of light beams emitted from the light source means when the plurality of light beams are incident on the deflection means is assumed to be α (rad), a distance from the deflection facet of the deflection means to a rotation center of the deflection means is assumed to be Ldef (mm), a focal length in the main scanning direction of the scanning optical system is assumed to be fk (mm), an angle defined in the main scanning direction between an optical axis of an incident optical system, which directs the light beams emitted from the light source means onto the deflection facet and an optical axis of the scanning optical system is assumed to be Q (rad), and a field angle in the main scanning direction defined between the principal ray of light beam deflected by the deflection facet and the optical axis of the scanning optical system is assumed to be θ (rad), the following expression is satisfied: {(α× Ldef )/(2× fk )}×{cos( Q /2)−sin( Q /2×tan θ}≦0.014.