ZOOM LENS

PURPOSE:To attain to make the zoom lens small in size and light in weight, while securing a variable power ratio by constituting a lens system consisting of five groups of lenses, and also, allowing it to satisfy specific conditions. CONSTITUTION:A lens system is constituted of five lens groups having refracting power of positive, negative, positive, positive and positive successively from an object side, a first, a third and a fifth lens groups 1, 3 and 5 are fixed, a second lens group 2 is moved for varying power, and a fourth lens group 4 is moved in order to correct a focal position. In such a state, when a focal distance of an i-th lens group, a focal distance of a wide angle end of the whole system, a curvature of an n-th boundary surface, and an n-th boundary surface interval are denoted as (fi), (fw), Rn and Tn, respectively, the lens system is allowed to satisfy expressions I - V. In such a way, a first lens group 1 can be converted to a small aperture, and also, even at the time of power focus, the motor torque can be reduced, and it can be attained to make the zoom lens small in size even in the case of a high variable power ratio.