Zoom objective with front and rear lens groups - has lens in first group having aspheric surface and second group incorporating diaphragm

摘要

Zoom objective reduces aberrations and has front and rear lens groups with respective negative and positive focal lengths. The front lens is a negative meniscus lens and its diameter is the largest in the zoom objective. The first lens group (I) has an aspheric surface. The second lens group (II) comprises a diaphragm of the zoom objective consisting of a positive lens, a double concave lens and a positive lens. The two lens groups (I, II) are separated by an air gap which is variable for the adjustment of the focal widths. The first lens group comprises an additional negative lens and the second lens group three additional positive lenses. The geometrical conditions included are that the ratio of the focal length of the first group to that of the overall focal length in the wide-angle position is between -3.0 and -1. 17.