A zoom lens system includes first to fifth lens groups arranged in this order from the object side. The first, third and fifth lens groups are fixed. The second lens group is moved in the direction of the optical axis of the zoom lens system when zooming the zoom lens system and the fourth lens group is moved in the direction of the optical axis to correct change in the image position due to the zooming and to correct change in the image position due to change in the object distance. The first lens group has a positive refracting power, the second lens group has a negative refracting power, the third lens group has a negative refracting power, the fourth lens group has a positive refracting power and the fifth lens group has a positive refracting power.

A telecentric zoom lens is disclosed that comprises, in order from the magnifying side to the reducing side on an optical axis: first, second, third, fourth, and fifth lens groups having a positive, negative, negative, positive, and positive focal length, respectively. An open aperture is axially disposed between the third and fourth lens groups at the magnifying-side focal position of the combined fourth and fifth lens groups. When zooming from the maximum wide-angle state to the maximum telephoto state, the first, fourth, and fifth lens groups are stationary, while the second lens group axially moves linearly toward the reducing side and the third lens group axially moves along a convex path toward the magnifying side.

A zoom lens system comprising at least five lens units, in order from the object side, of a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a negative refractive power, a fourth lens unit having a positive refractive power and a fifth lens unit having a positive refractive power. This zoom lens system is configured so as to change a magnification thereof by moving the first through fifth lens units, and has wide field angles, a high vari-focal ratio and a compact size.

A zoom lens of the rear focus type is disclosed comprising, from front to rear, a first lens unit of positive refractive power, a second lens unit of negative refractive power, a third lens unit of positive refractive power and a fourth lens unit of positive refractive power, the second and fourth lens units axially moving to effect zooming, and the fourth lens unit axially moving to effect focusing. The third lens unit includes at least one positive lens at a front position and a negative lens of meniscus form concave toward the image side at a rearmost position. The fourth lens unit includes one negative lens and two positive lenses. The focal lengths f3 and f4 of the third and fourth lens units, respectively, satisfy the following condition:

First, second, third, and fourth lens groups, from an object side, have positive, negative, negative, and positive power, respectively. Movable second and third lens groups vary magnification and perform focus compensating. The fixed fourth lens group has an image forming function, and includes, from the object side, positive first and second lens sub-groups. The zoom lens satisfies the following relationships: L.sub.W2-3 represents a distance between the second and third lens groups, f.sub.w represents a focal length of the entire lens system, and m.sub.2W represents a lateral magnification of the second lens group, each at a shortest focal length. Further, m.sub.4 and m.sub.4b represent lateral magnifications of the fourth lens group and the second lens subgroup of the fourth lens group, respectively.