Zoom lens system capable of wide-angle viewing for high zoom ratio

摘要

A zoom lens system capable of wide-angle viewing for a high zoom ratio has four lens groupss, all of which change the focal length of the overall system while the position of the image plane is held constant. The second lens group comprises a negative lens element having a concave surface of large curvature on the image side, a biconcave negative lens element that is cemented to a positive lens element to provide a cemented surface that has a large curvature and which is convex toward the object, and a negative lens element whose surface on the object side has a large curvature and is concave toward the object. The fourth lens group comprises a front subgroup having a positive focal length which is composed of one or two positive lens elements having a convex surface on the object side and at least one negative lens element, a middle subgroup composed of a negative lens element that is cemented to a positive lens element to provide a cemented surface that has a large curvature and which is divergent and convex toward the object, and a rear subgroup composed of a positive lens element and a negative meniscus lens element whose surface on the object side has a large curvature and is concave toward the object.