| 摘要 |
PROBLEM TO BE SOLVED: To improve fθcharacteristics, namely, distortion and image surface property in the main and sub scanning direction in spite of being a laser scanning optical system, by introducing an axially asymmetrical and non-spherical surface which is not symmetrical with respect to the main scanning direction. SOLUTION: A scanning lens group is provided with axially symmetrical two lenses respectively provided with surfaces r1, r2 and surfaces r3, r4 and one axially asymmetrical lens with surfaces r5 and r6. The symmetrical axes of the two axially symmetrical lenses are coincident with each other. In addition, a surface to be scanned (namely the surface of a photosensitive body 7) r7 is vertical to a light axis with respect to the main scanning direction shown by an arrow A. Concerning the axially asymmetrical lens, a surface r6 on a side emitting image light is a plane and vertical to the light axis. On the other hand, the surface r6 on a side image light enters is not symmetrical axially. In addition the subscanning direction shown by an arrow B is provided with refracting power stronger than that of the main scanning direction. |
