| 摘要 |
PURPOSE:To improve field curvature, a spot diameter and an ftheta characteristic due to an optical scanning system constituted of a plastic lens and to eliminate the unstableness of lens performance according to the fluctuation in a focal position due to the temperature change. CONSTITUTION:The optical scanning optical system is constituted of a semiconductor laser 10, a collimate lens 11 making the diverging light thereof parallel light rays, a cylindrical lens 14 in a first image forming optical system having power only in sub-scanning, a deflector 15 having a deflection surface for deflecting a luminous flux in the vicinity of the image point of the first image forming optical system and a second image forming optical system for image forming the luminous flux deflected by the deflector 15 on a photosensitive body drum 20. Then, the second image forming optical system is constituted of three pieces of a first lens 16 with negative power, a second lens 17 with positive power and a third lens 18 consisting of a deformed cylindrical lens surface making the surface of the photosensitive body drum 20 side an aspherical surface from the deflector 15 successively, and the deformed cylindrical lens is movable at the time of the temperature change. |
