| 摘要 |
PURPOSE:To sufficiently obtain a high picture quality having no variation of a reflecting point and having a uniform focus, by a simple device whose optical member and its arrangement, etc., are manufactured in a standardized procedure by providing a curved specular surface opposed to a rotary polygon mirror whose axis is the center of curvature, in the periphery of the rotary polygon mirror. CONSTITUTION:In the periphery of a rotary polygon mirror 4, a curved specular surface 11a opposed to the rotary polygon mirror 4, in which an axis X of the rotary polygon mirror 4 is the center of curvature is provided, and the specular surface 11a has a radius of curvature being equal to two times of a distance between the axis X and the reflecting surface. When a light beam 2 is projected to the center O of the rotary polygon mirror 4, the light beam 2 is reflected in the direction corresponding to a direction of a reflecting surface 4a when it is made incident on the reflecting surface 4a and reaches the curved specular surface 11a, reflected and turned to the reflecting surface 4a again, and reflected again on the reflecting surface 4a. A triangle for connecting first and second reflecting points P3, P1 and its intermediate reflecting point P2 is symmetrical to a triangle for connecting the first and the second reflecting point P3, P1 and the center point O, by setting the reflecting surface 4a as a boundary, the incident direction of the light beam 2 turns to the center O, and the reflecting point can be made immobile substantially. In such a way, a part whose focal shift is large is not generated, therefore, high accuracy is unnecessary. |
