Patent ID: 8872871

Claim:
A light scanning unit comprising: a light source emitting a light beam according to an image signal; a light deflector deflecting and scanning the light beam emitted from the light source; and a synchronization detection optical system comprising a synchronization detection sensor detecting a synchronization signal by receiving a portion of the light beam that is deflected and scanned by the light deflector and a synchronization detection lens disposed between the light deflector and the synchronization detection sensor, wherein the synchronization detection lens is an anamorphic lens in which refractive power in a first direction and refractive power in a second direction different from the first direction are different, and wherein the first direction of the synchronization detection lens is inclined with respect to a main scanning direction in which a light beam incident on the synchronization detection lens is scanned, wherein when viewed along a sub-scanning cross-section that is orthogonal to the main scanning direction, the light beam emitted from the light source is obliquely incident on a deflection surface of the light deflector, wherein an angle Δθ between the first direction of the synchronization detection lens and the main scanning direction is determined by an incident angle α and an incident angle β of the light beam respectively proceeding to the synchronization detection lens in the main scanning direction and the sub-scanning direction with respect to the light deflector the angle Δθ being independent of a degree of a surface collapse of the light deflector, and wherein the angle Δθ between the first direction of the synchronization detection lens and the main scanning direction is expressed by the following equation: Δθ=arctan(tan α·tan β). <Equation>