JPS6423215A - Lens for reading original - Google Patents

Abstract

PURPOSE:To constitute a lens which is bright and has a wide view angle and high resolution, by constituting said lens of five groups and seven pieces, and setting a specific conditional expression between a focal distance of the whole system and a focal distance of the first group. CONSTITUTION:The titled lens is constituted of five groups and seven pieces, and constituted of the first group of two pieces of meniscus lenses whose convex surface is faced to an object, the second meniscus group whose convex surface is faced, the third meniscus group whose convex surface is faced to an image surface side, the fourth group of a biconcave lens and a lens whose convex surface is faced to the image surface side, and the fifth group of a parallel plane lens, from the object side. When the refracting power of the first group is too strong, the view angle becomes narrow, and when said power is too weak, the performance of an image height intermediate part is deteriorated. When a conditional expression is set between a focal distance (f) of the whole system and a focal distance f12 of the first group, an aberration is corrected satisfactorily. Accordingly, by a device which is bright and compact, and has a wide view angle and high resolution, it can be realized to read at high speed.