Infrared zoom lens and infrared camera with three lens groups

摘要

An infrared zoom lens has first to third lens groups (G1, G2, G3) in this order from the object side. At the zooming time, said second lens group (G2) is moved and said first (G1) and third lens groups (G3) are fixed. Each of said first to third lens groups has one lens formed of zinc sulphide. The following condition is satisfied: -1.25 < f2/ft < -0.34, where ft: Focal length of most telephotographic side of whole of first to third lens groups, and f2: Focal length of second lens group.