Zoom lens system

A zoom lens system comprising, in the order from the object side, a first lens unit having positive refractive power, a second lens unit having negative refractive power, a third lens unit having positive refractive power and a fourth lens unit having positive refractive power, said first lens unit and said fourth lens unit being fixed at the zooming time of said zoom lens system, whereas said second lens unit and said third lens unit being shifted along the optical axis while varying the airspace reserved therebetween for varying focal length and compensating shift of the imaging position, said second lens unit consisting of, in the order from the object side, a negative lens element having a strongly concave surface on the image side and another negative lens element, said third lens unit consisting of a single positive lens element, and magnification .beta..sub.2T of said second lens unit at the tele position satisfying the following conditions:

• .vertline..beta..sub.2T .vertline.<1

A zoom system comprising, in the order from the object side, a first lens unit having positive refractive power, a second lens unit having negative refractive power, a third lens unit having positive refractive power and a fourth lens unit having positive refractive power, adapted in such a manner that said first lens unit and said fourth lens unit are fixed at the zooming time, whereas said second lens unit and said third lens unit are shifted in the same direction along the optical axis while varying the airspace reserved therebetween for varying focal length and compensating deviation of the imaging position, and comprising a graded refractive index lens in said lens system.