Of the three-group zoom lens focusing system

摘要

PURPOSE: To provide a focusing method for a zoom lens showing good performance extending from far distance to very near distance in spite of having the less number of constituting lenses, a small size and being low in cost. ;CONSTITUTION: In the zoom lens formed out of a first group G1 having extremely weak refracting power, a second group G2 having positive refracting power, and a third group G3 having negative refracting power in which power variation is performed by changing each space between the respective groups, the first group G1 contains at least one aspherical face, all the lenses contained in the first group G1 are formed out of lenses having extremely weak refracting power, and at focusing, the first group G1 and the second group G2 are moved on the optical axis, or the second group G2 is moved on the optical axis.;COPYRIGHT: (C)1995,JPO