| 摘要 |
PURPOSE:To simplify an optical system having a high resolution, and to obtain it at a low cost by constituting a scanning lens of two pieces of lenses consisting of a plane-concave lens which has been placed so that the plane side is opposed to a rotary polygon mirror deflecting device, and a cylindrical convex lens which has been placed between the plano-concave lens and a place to be scanned and has a power only in the surface in the direction vertical to the deflecting scanning surface. CONSTITUTION:A meridional luminous flux is emitted so as to form an image at a point P' existing between a deflecting mirror SM and a place to be scanned S1 from the deflecting mirror SM of a rotary polygon mirror, passes a plano-concave lens 1, and a cylindrical convex lens 2, and forms an image at a point P on a point S1 of the plane to be scanned. In these lenses, the cylindrical convex lens 2 has no curvature in the meridional direction, therefore, no influence is exerted on a curve aberration of the meridional image surface. Accordingly, the meridional image surface curve aberration can be corrected by the plano-concave lens 1. In this way, by using the plano-concave lens, the meridional image surface curve can be suppressed small, it becomes more inexpensive than a lens whose both faces have a curvature, and also, since it can be attached and positioned easily, an optical scanner can be obtained at a low cost. |
