Zoom lens system having third lens group with air lens formed of adjacent negative and positive single lens elements

A zoom lens system comprising a negative first lens group, a positive second lens group, a negative third lens group and a positive fourth lens group, in that order from the object side,

• wherein upon zooming from a short focal length extremity to a long focal length extremity, at least said first lens group, said second lens group and said fourth lens group are moved in the optical axis direction of the zoom lens system,
• wherein said third lens group includes a negative first sub-lens group and a negative second sub-lens group, in that order from the object side,
• wherein said second sub-lens group is provided with a negative single lens element and a positive single lens element, and an air lens having a positive focal length is provided between said negative single lens element and said positive single lens element, and
• wherein said a negative single lens element has a concave surface on the image side, and said positive single lens element has a convex surface on the object side, in that order from the object side, wherein said negative single lens element and said positive single lens element are immediately adjacent to each other and wherein said air lens is meniscus-shaped and has a convex surface on the object side,
• wherein the following relationship is satisfied:
• 0.1<Ri/Ro<1.1
• wherein
• Ri designates a radius of curvature of an image side surface of said meniscus-shaped air lens provided within said second sub-lens group, and
• Ro designates a radius of curvature of an object side surface of said meniscus-shaped air lens provided within said second sub-lens group.