Cushman, Darby & Cushman
Compact zoom lens system
 A compact zoom lens system is disclosed having a first lens group with positive refractive power, a second lens group with negative refractive power, a third lens group with positive refractive power, and a fourth lens group with negative refractive power, such that the second and third lens groups are moved for the purpose of zooming, and the first lens group is moved in order to compensate for the movement of image surface, the entire system having a large zoom ratio. 
Olympus Optical Co., Ltd.
G G
G02B G02B
inventional inventional
Tooru
Fujii