| 摘要 |
PURPOSE:To sufficiently obtain a high picture quality having no variation of a reflecting point and having a uniform focus, by a device whose optical member and its arrangement, etc., are manufactured in a standardized procedure and to reduce the cost, by providing a specular surface faced in parallel to each reflecting surface of a rotary polygon mirror for scanning. CONSTITUTION:When a light beam 2 is projected to the center 0 of a rotary polygon mirror 4, the light beam 2 is reflected with an angle of reflection in accordance with a direction to the light beam 2 by a reflecting surface 4a of the rotary polygon mirror 4. On the other hand, a specular surface 11a which is parallel to the reflecting surface 4a, and also, which is in a position where a distance to the reflecting surface 4a is equal to a distance to the center O always holds a position relation by the same body-like movement with the rotary polygon mirror 4, receives a reflected light from the reflecting surface 4a, and turns it to the original reflecting surface 4a. The reflecting surface 4a reflects the light beam 2 from the specular surface 11a, in the radiation direction from the center O, therefore, the surface 4a is assumed as a surface where a reflecting point always exists in the center position O of the rotary polygon mirror 4, and the reflecting point is immobile. In such a way, a part whose focal shift is large is not generated, therefore, it becomes unnecessary to place an optical system with high accuracy, and the manufacture of an image forming device can be standardized and the cost can be reduced. |
