| 摘要 |
PURPOSE: To make an image point draw an almost rectilinear locus over the width of a scanning surface by constituting a correction optical system of two curved surface mirrors alternately arranged in the optical path of a scanning beam and making the optical distance between a main image-formation optical system and a minimum focusing point hardly depend on a deflection angle. CONSTITUTION: The correction optical system is provided with the curved surface mirrors 51 and 52. The mirror 51 is convex and hyperbolically cylindrical and its bus is parallel with the rotary shaft line of a rotary mirror 40, and the mirror 52 is concave and parabolically cylindrical. The optical distance between a light source 10 and the scanning surface 61 is made equal to the position of an objective lens system 30 whatever adjustment (rotational angle) of a deflection optical system 42 is performed. In the case of changing the deflection angle of the optical system 42, the incident position of the beam made incident on correction optical elements 51 and 52 is also changed in the optical path of the beam, and the optical performance of the elements are changed. Therefore, the light source 10 performs image-formation at the same distance. The locus drawn by the image point formed in such a way becomes an accurate straight line on the surface 60. |
