PURPOSE: To compensate the performance of lenses over the whole focal distance by constituting a zoom lens system by the 1stW4th lens groups having negative, positive, and positive composite refractive powers respectively which are succesively aligned from the object side and positively contributing the air spaces between said lens groups to the compensation of aberrations.

CONSTITUTION: A titled lens system is constituted by the 1st lens group L1 having negative composite refractive power, the 2nd lens group L2 with positive composite refractive power, the 3rd lens group L3 with negative composite refractive power, and the 4th lens L4 with positive composite refractive powers which are aligned succesively from the object side. When the forcal distances of the whole system are changed by changing the air spaces between the 1stW 4th lens groups, the air space between the 1st and 2nd lens groups and that between the 3rd and 4th lens groups in the short focus side are reduced in the long focus side and the air space between the 2nd and 3rd lens groups in the short focus side is increased in the long focus side. When f1Wf4 are defined as the focal distances of the 1stW4th lens roups, conditions f2<f1, f3<f4 and (2) f2<f3are satisfied. Consequently, a lens system with about 76° image angle, a about 3 times zoom ratio and efficient aberration is obtained.