| 摘要 |
PURPOSE:To allow dealing with a large polarization angle and high resolution by constituting the scanner in such a manner that the radii of curvature of the cylindrical faces of a lens group constituting an optical system for focusing a deflected light beam onto an object to be scanned so as to satisfy specific conditions. CONSTITUTION:The optical system between a rotary polyhedral mirror 8 of the optical beam scanner and the object 9 to be scanned consists of a lens 1, one face of which is a cylindrical face 1a and the other a spherical face, a lens 2 one face of which is a cylindrical face 2a and the other a plane 2b, and a lens 3 one face of which is a plane 3a and the other is a troidal face 3b. The curvature of field in the sub-scanning direction is well corrected by decreasing the value of R3 and increasing the value of R4 if the radius of curvature of the face 1a is designated as R3 and the radius of curvature of the face 2a as R4. The correction effect is remarkable particularly under the condition under which the relation of R3 and R4 attains (1/R3)>(1/R4). The curvatured of field in the sub-scanning direction is thus confined practicably within the range where there are substantially no problems. |
