Patent ID: 8259149

Claim:
An image forming apparatus that forms an image according to image data, the image forming apparatus comprising: a light source that emits a light beam according to the image data; a deflecting unit that receives the light beam from the light source and deflects the light beam in a main-scanning direction; a scan-start-synchronization control sensor that detects the light beam near a scan-start position in the main-scanning direction; a scan-end-synchronization control sensor that detects the light beam near a scan-end position in the main-scanning direction; a plurality of photosensitive elements that are exposed to the light beam received from the deflecting unit; and a light-beam control unit that controls an emission of the light beam from the light source depending on a distance between the deflecting unit and the photosensitive elements, thereby performing an fθ correction of the light beam, wherein the deflecting unit includes a rotatable polygon mirror having a plurality of first reflection surfaces, each corresponding to one of the photosensitive elements, the rotatable polygon mirror having two second reflection surfaces, one of the second reflection surfaces receives the light beam and reflects the light beam to the scan-start-synchronization control sensor, an other of the second reflection surfaces receives the light beam and reflects the light beam to the scan-end-synchronization control sensor, the first reflection surfaces reflect the light beam at reflection angles that differ from one another, the second reflection surfaces reflecting the light beam at reflection angles that differ from one another, and the second reflection surfaces are smaller than the first reflection surfaces in length in the main-scanning direction of the light beam.