| 摘要 |
PURPOSE:To easily and securely remove the curvature of field in a subscanning direction and to make a high-density optical scan by providing a focal length varying means which varies the focal length of a cylindrical lens in synchronism with the optical scanning of deflected luminous flux. CONSTITUTION:Substrates 13A and 13B of the cylindrical lens 2A are provided with transparent electrodes, through which a voltage V can be applied from an applying means 15, so that an electric field is activated on liquid crystal 12 by the voltage application. The refractive index of the liquid crystal 12 is expressed as the function n(V) of the voltage applied from the applying means 15 and the distance bfcv from the substrate 13A to the focus can be varied by controlling the applied voltage V. Here, the curvature of field in the subscanning direction can be removed by controlling the applied voltage V so that the curvature of field in the subscanning direction is corrected according to the optical scanning. Consequently, the curvature of field in the subscanning direction can easily and securely be removed, the diameter of a light spot in the subscanning direction can be uniformed, and the high-density scan can be made. |
