| 摘要 |
PURPOSE:To obtain an image forming lens which is short in back focus, can be widened in angle, and has ftheta characteristics of distortion by providing an ftheta lens which consists of two convex lenses and is a convex meniscus lens whose surface closest to an entrance pupil is concave to the pupil side. CONSTITUTION:The ftheta lens consists of two positive and positive lens elements, and its front group convex lens is a positive meniscus lens having its concave surface at the entrance pupil as a deflecting surface for a beam and is aplanatic. The back focus is shortened by arranging the convex lens in the front group and a rear group lens where an incident beam is passed at high height from the optical axis is made convex to generate negative distortion, thereby obtaining ftheta characteristics or characteristics close to them. |
