| 摘要 |
PURPOSE:To provide a telecentric ftheta lens with simple composition and excellent performance. CONSTITUTION:This device is arranged with a first to a third groups succesively from the side of an optical deflector 3 toward the side of the surface to be scanned 7, the first group is composed of a meniscus lens whose convex surface confronts the side of deflector and not nearly having a refractive power, by representing the radii of curvature of the lens surfaces of the first group successively from the side of the deflector by R1, R2 and the focal distances of the second and the third groups by f2 and f3 respectively, the conditions (1) 0.9<R1/R2<1.2, (2) 0.6<f2/f3<1.2 are satisfied. |
