| 摘要 |
PURPOSE:To obtain an optical system of high resolving power which has a tilt correcting function by inverting and arranging a system which has a negative refracting power group on the side of a deflector and a positive refracting power group on the side of a surface to be scanned arranging like the arrangement constitution of an ftheta lens. CONSTITUTION:A 1st image formation optical system forms the image of luminous flux emitted by a light source part linearly, and the rotary polygon mirror type deflector which has its deflecting and reflecting surface nearby the linear image formed by the 1st optical system, and the luminous flux deflected by the deflector is scanned on the object medium, and a 2nd image formation optical system is provided between the medium and deflector. Then the 2nd image formation optical system consists of a front group consisting of a spherical lens with positive refracting power, a cylindrical lens part with positive refracting power, and a rear group consisting of plural spherical lenses with negative refracting power in order from the deflector side reversely from a conventional example. Thus, the front group with the positive refracting power and the 2nd image forming lens are arranged on the deflector side and then a light beam which is deflected through the deflector by a half scan angle slants almost equally to the optical axis and enters the cylindrical lens. |
