| 摘要 |
PURPOSE:To effectively reduce or remove the unbalance of a spot by gradually reducing the power of a subscanning direction on an image face curve connecting face in accordance with separation from an optical axis in a direction corresponding to main scanning. CONSTITUTION:On a lens face 20A correcting the image face curve the radiuses RYO, RXO of curvature of curvature circles CAY, CAX in main and subscanning directions on an optical axis position are equal and the radius RX1 of the curvature circle CAX in the subscanning direction is gradually increased in accordance with separation from the optical axis in the direction corresponding to the main scanning. Thereby, positive power in the subscanning direction on the lens face 20A is high at an optical axis part and is gradually weakened in accordance with separation from the optical axis in the main scanning direction. Thereby, the power of a whole 2nd lens group in the subscanning direction is also high at the optical axis part and is gradually weakened in accordance with the separation from the optical axis in the main scanning direction, so that the image face curve of the whole 2nd lens group in the subscanning direction can be effectively corrected. Consequently, the variation of a spot shape on the scanning face can be effectively reduced or removed and the optical scanner can be allowed to correspond to optical scanning with high resolution. |
