| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a scanning optical device being compact and suitable for high-accuracy printing by suitably setting a lens shape of an fθ lens. <P>SOLUTION: A scanning optical device has light source means, a rotary polygon mirror for deflective reflection of a light flux emitted from the light source means, and an imaging optical system for imaging the light flux deflectively reflected on a deflection face of the rotary polygon mirror onto a face to be scanned. In a main scanning cross section, a light flux entering the deflection face of the rotary polygon mirror enters diagonally to a light axis of the imaging optical system. The imaging optical system has at least one imaging lens, where the sub-scanning direction curvature of at least two lens surfaces of at least one imaging lens continuously changes from the on-axis towards the off-axis asymmetrically to the light axis so that the condition of Fmin/Fmax≥0.9 is satisfied when a maximum value of F number in the sub-scanning direction of a light flux entering a face to be scanned is defined as Fmax and a minimum value of F number in the sub-scanning direction of the light flux entering the face to be scanned is defined as Fmin. <P>COPYRIGHT: (C)2012,JPO&INPIT |
