| 摘要 |
PURPOSE: To excellently correct an fθcharacteristic in the horizontal scanning direction and the curvature of field by making at least one lens surface an aspheric surface assymetric in the horizontal scanning direction and/or vertical scanning direction with respect to the optical axis center of an image-forming means. CONSTITUTION: The image forming means (fθlens system) 10 is constituted of three lenses, that is, a toric lens 6 having negative refracting power on a horizontal scanning cross section and positive refracting power on a vertical scanning cross section, an anamorphic lens 7 arranged in the vicinity of the side of the surface to be scanned of the toric lens 6 and having the positive refracting power being mutually different on the horizontal scanning cross section and the vertical scanning cross section and the toric lens 8 arranged in the vicinity of the side of the surface to be scanned of the anamorphic lens 7 and having the positive refracting power on the horizontal scanning cross section and the negative refracting power on the vertical scanning cross section. The toric lens 8 is formed to be a concentric shape, and its lens surface on the side of a light deflector 5 in the horizontal scanning direction is made to be a symmetrical aspherical shape with respect to the optical axis center, and its lens surface on the side of the surface to be scanned is formed to be the asymmetrical aspherical shape with respect to the optical axis center. |
