Zoom-lens system (varifocal system, variable-focus-lens system)

摘要

A compact zoom lens system having a zoom ratio greater than 3.0 comprises a first positive lens group I, a second positive lens group II spaced from said first lens group at a first distance, and a third negative lens group III spaced from the second lens group at a second distance, the first and second distances being variable during zooming, wherein 3.0 < fT/fW, and optionally LT/fT < 1.0 where fT is the focal length of the zoom lens system at a telephoto position, fW is the focal length of the zoom lens system at a wide angle position, and LT is the distance from the first surface of the zoom lens system to the image plane at a telephoto position, or f1/ft < 0.55 where f1 is the focal length of the first lens group.