Patent ID: 7315422

Claim:
An image forming device comprising: a zoom lens system including a plurality of lens units and performing magnification varying by changing a distance between the lens units; and an image sensor that converts an optical image formed by the zoom lens system into an electric signal, wherein the zoom lens system includes three lens units of, from an object side, a first lens unit having negative optical power, a second lens unit having positive optical power and a third lens unit having positive optical power, the second lens unit includes three single lens elements of, from the object side, a positive lens element, a negative meniscus lens element convex to the object side and a positive lens element, and the following conditions are satisfied: 1.0 <|P 22 /P 21|<2.0 and 1.5 <|f 1 ×fw/Lw |<2.0 where P21: optical power of the object side positive lens element in the second lens unit, P22: optical power of the negative meniscus lens element in the second lens unit, f1: a focal length (mm) of the first lens unit, fw: an overall focal length (mm) of the zoom lens system at the wide angle end, and Lw: an overall optical length, that is, a length from a most object side surface of the zoom lens system to an image surface, at the wide angle end.