Cushman, Darby & Cushman
Vari-focal photographic lens system of lens group exchange type
 A vari-focal photographic lens system of lens group exchange type comprising, in the order from the object side, a first lens unit having positive refractive power, a second lens unit having negative refractive power, and a third lens unit having negative refractive power, the vari-focal photographic lens system being arranged to vary the focal length thereof by exchanging the second lens unit for another second lens unit having different lens configuration. 
Olympus Optical Co., Ltd.
G
G02B
inventional
Masaki Hiroshi Toru
Imaizumi Takase Fujii