Patent ID: 7808720

Claim:
A standard zoom lens system comprises a negative first lens group, a positive second lens group, and a positive third lens group, in this order from an object, wherein upon zooming from the short focal length extremity to the long focal length extremity, the distance between said negative first lens group and said positive second lens group decreases, and the distance between said positive second lens group and said positive third lens group increases; wherein said negative first lens group comprises a negative lens element and a positive lens element, in this order from the object; wherein the most image-side surface of the positive second lens group comprises a concave surface; and wherein said standard zoom lens system satisfies the following conditions: 0.15 <Rs/fT< 0.173 wherein Rs designates the radius of curvature of the most image-side surface of said positive second lens group (Rs>0); and fT designates the focal length of said entire standard zoom lens system at the long focal length extremity when an object at an infinite distance is in an in-focus state; and 1.65<NP2 wherein NP2 designates the refractive index of the d-line of the most object-side positive lens element of said positive second lens group; wherein said positive lens element of said negative first lens group comprises a plastic lens element having at least one aspherical surface.