| 摘要 |
PURPOSE:To correct the deviation of a beam spot in the subscanning direction of an optical deflector and to correct aberrations on a scanning image formation surface by providing a concave cylinder lens surface as one surface of an ftheta lens, and moving and adjusting a convex cylinder lens in an optical-axis direction. CONSTITUTION:This scanner consists of an irradiating means which projects a beam 1 from a light source as nearly parallel luminous flux with a specific diameter, the optical deflector 2 which deflects the luminous flux from its, an image forming lens system 3 which forms the image of the deflected luminous flux, and the convex cylindrical lens 6 arranged between the lens system 3 and scanning image formation surface 7. The image forming lens system 3 consists of the ftheta lens composed of plural lens elements and at least one of its surfaces is made into an infinite-curvature surface to form the concave cylinder lens surface 4, thereby making the focus position P0 in the main scanning direction coincident with the scanning image formation surface 7. Further, the convex cylindrical lens 6 is moved and adjusted by DELTAx in the optical-axis direction to move the focus position P1 in the subscanning direction in the optical-axis direction from a specific quantity from the scanning image formation surface 7, thereby nearly equalizing the beam diameter in the subscanning direction on the scanning image formation surface 7 to the beam waist Wd in the main scanning direction. |
