Optical scanning device and image forming apparatus using the same

An optical scanning device, comprising:

• a light source unit having a plurality of light emitting members of a number N, with N being an integer not less than 2, disposed with a tilt with respect to a sub-scan direction and a main-scan direction;
• an input optical system configured to direct N light beams emitted by said N light emitting members;
• a deflecting unit comprising a deflecting surface and configured to scanningly deflect the N light beams directed to said deflecting unit by said input optical system, wherein the N light beams are eclipsed differently by said deflecting surface of said deflecting unit, such that a predetermined light beam, emitted by a predetermined light emitting member of said N light emitting members, is eclipsed more than other light beams of the N light beams;
• a synchronism signal detecting unit configured to detect one of the N light beams scanningly deflected by said deflecting surface so as to produce a synchronization signal for determining writing start timing signals for the N light beams upon a surface to be scanned, wherein the detected light beam is emitted from a light emitting member other than the predetermined light emitting member;
• a synchronism detecting optical system configured to direct the N light beams from said deflecting unit to said synchronism signal detecting unit;
• and
• an imaging optical system configured to direct the N light beams scanningly deflected by said deflecting surface to the surface to be scanned,
• wherein said deflecting unit is further configured such that a portion of the predetermined light beam is eclipsed by said deflecting surface, and the synchronism detecting optical system is configured such that the eclipsed predetermined light beam is then incident on said synchronism signal detecting unit, and
• wherein the detected light beam is the light beam of the N light beams which scans the surface to be scanned the latest with respect to the other light beams of the N light beams, and said synchronism signal detecting unit produces the synchronization signal from which the writing start timing signals for the N light beams are determined in conjunction with respective premeasured time delays.