| 摘要 |
PROBLEM TO BE SOLVED: To provide an image forming lens for scanning capable of all the more improving the constant speed characteristic and the curvature of field. SOLUTION: This lens is an image forming lens for scanning used in an optical scanning device for converging a light beam deflected by a light deflector 4 on a surface to be scanned 7 as a light spot by means of image forming lenses for scanning 5, 6 and optically scanning the surface to be scanned 7 at a constant speed, comprises a scanning lens 5 having the function of converging the deflected light beam and making the optical scanning of the surface to be scanned 7 almost uniform speed and a correcting lens 6 for forming the image of the deflected beam near the surface to be scanned in cooperation with the scanning lens 5, the scanning lens 5 is composed of two spherical lenses, the correcting lens 6 is a long-length toroidal lens including a barrel- shaped toroidal surface as a concave surface whose radius of curvature in the direction corresponding to sub-scanning becomes smaller as it is separated apart from the optical axis in the direction corresponding to main scanning and the shape of the barrel-shaped toroidal surface is not circular-arcuate. |
