US Patent 7286274 Optical scanner and image forming apparatus using the same

The invention aims at provision of an optical scanner in which an optics required for equalizing an optical magnification in a scanning range is produced with high accuracy, so that intervals among a plurality of scanning lines on a to-be-scanned surface are even in the scanning range. The scanning optics includes a refraction surface and a reflection surface whose sub-scanning-direction curvature radii vary continuously. The reflection surface is disposed on the to-be-scanned surface side of the refraction surface. The curvature radius of the reflection surface varies symmetrically with respect to the optical axis, and the curvature radius of the refraction surface varies asymmetrically with respect to the optical axis.