Variable magnification copying lens system

Abstract

A variable magnification copying lens system with the arrangement composed, in order from the object side, of a first lens unit (A) having a negative focal length, a lens group (B) having a positive focal length, and a second lens unit (C) having a negative focal length. The system being capable of maintaining a constant distance between the object surface and the image surface not only by changing the distance between the first lens unit (A) and the lens group (B) and that between the lens group (B) and the second lens unit (C) but also by moving the overall lens system. The first and second lens units (A) and (C) have the primary function of maintaining a constant distance between the object surface and the image surface by a substantially symmetrical movement with respect to the lens group (B). Each of the first and second lens units being simply made of a single negative lens. The lens group (B) has the primary function of zooming and a five-unit and five-element configuration composed of a center biconvex lens, a negative meniscus lens that is positioned on both sides of the biconvex lens and the concave surface of which is directed toward the center, and a positive meniscus lens that is positioned on the outer side of the negative meniscus lens and the concave surface of which is directed toward the center.