Optical scanning apparatus and color image forming apparatus

An optical scanning apparatus comprising:

• a plurality of light source units;
• a deflecting unit having a plurality of deflecting surfaces, the deflecting surfaces configured to deflect and scan light beams emitted from the light source units;
• a plurality of incident optical systems configured to direct the light beams emitted from the light source units to the different deflecting surfaces of the deflecting unit, the incident optical systems provided so as to correspond to the light source units;
• a plurality of imaging optical systems configured to image the light beams on a plurality of surfaces to be scanned, the imaging optical systems arranged in optical paths of the light beams deflected and scanned by the different deflecting surfaces of the deflecting unit;
• and
• a synchronous detection optical system configured to determine a timing at which the light beams form images on the surfaces to be scanned;
• wherein, in a main scanning cross-section, the imaging optical systems are arranged to oppose each other with the deflecting unit therebetween;
• and
• wherein the synchronous detection optical system includes a synchronous detection element configured to detect one of the light beams deflected and scanned by the deflecting surface of the deflecting unit, at least one optical path changing unit arranged in an optical path between the deflecting unit and the synchronous detection element, the optical path changing unit configured to change an optical path of said one of the light beams deflected and scanned by the deflecting surface of the deflecting unit and direct said one of the light beams to the synchronous detection element, and at least one synchronous detection optical element arranged in an optical path between the optical path changing unit and the synchronous detection element, the synchronous detection optical element having a refractive power at least in a main scanning direction,
• wherein the synchronous detection element is attached to a substrate of the light source unit arranged to oppose the light source unit that emits the light beam used for synchronous detection, with the deflecting unit therebetween, in the main scanning cross-section, and
• wherein the synchronous detection optical element and the synchronous detection element are arranged to oppose each other with respect to a straight line perpendicular to lines connecting a deflection axis of the deflecting unit and optical axes of the imaging optical systems, in the main scanning cross-section.