| 摘要 |
PURPOSE:To obtain an ftheta lens which has sufficient performance with simple single-element constitution even when its refractive index is <=1.6, and can be molded out of even a plastic material by specifying the relation among the focal length, deviation from a surface with a radius of paraxial curvature as an object-side surface, and deviation from a surface with a radius of paraxial curvature as an image-side surface. CONSTITUTION:On a single lens which is provided with an entrance pupil in front of the lens and has positive power, at least one surfacve is made aspherical surface and satisfies an inequality 1. In the inequality, (f) is the focal length, DELTAX1 is the deviation from the surface with the radius of paraxial curvature as the object-side surface, and DELTAX2 is the deviation from the surface with the radius of paraxial curvature as the image-side surfade; and an equation (2) holds. Subordinately, -0.5<f/R1<0.5 (R1: radius of paraxial curvature on object side) and the single ftheta lens satisfying the inequality is constituted. The upper limit of the inequality 1 is a limit for obtaining the correction effect of an merdional image plane and the lower limit is a limit where the compensa tion becomes excessive and a limit for preventing the distortion aberration from becoming too positive. |
