Patent ID: 6914620

Claim:
A multi-beam scanning optical system comprising: light source means; incident optical means for guiding a plurality of light beams emitted from said light source means to deflection means; scanning optical means for imaging the plurality of light beams deflected by said deflection means on a surface to be scanned; and synchronization detection optical means in which the plurality of light beams deflected by said deflection means are condensed on a slit surface of a slit or a vicinity thereof by an optical element and then guided to a synchronization detection element, and timing of a scanning start on the surface to be scanned is controlled with respect to the plurality of light beams by using a signal from said synchronization detection element, wherein a first light beam limiting element is provided between said deflection means and said optical element closest to said deflection means, and wherein said incident optical means has a second light beam limiting element and, given that a distance from said second light beam limiting element to a deflection point on said deflection means is d [mm], a maximum value of a distance in a main scanning direction between light-emitting portions of the plurality of light beams is w [mm], a focal length within a main scanning cross section of said incident optical means is fn [mm], and a focal length within a main scanning cross of said scanning optical means is fs [mm], the system satisfies a conditional expression (d·w)/(fn·fs)≦0.003.