Patent ID: 8159756

Claim:
A vari-focal length lens system comprising: a first lens group having a positive refractive power; a second lens group having a negative refractive power; a third lens group having a positive refractive power, and a fourth lens group having a positive refractive power, wherein said first to fourth lens groups are arranged from an object side to an image side, when a positional lens state is changed from a wide angle end state to a telephoto end state, a distance between said first lens and said second lens increases, a distance between said second lens and said third lens decreases, and a distance between said third lens and said fourth lens varies, when said positional lens state is changed from a wide angle end state to a telephoto end state, all of said lens groups are movable, an aperture stop is arranged near said third lens group, and said fourth lens group moves at the time of short distance focusing, said first lens group includes a negative lens with a concave that faces to an image and a positive lens with a convex that faces an object, which are arranged from said object side to said image side in this order said second lens group includes a negative lens with a concave side to said image, a negative lens with a concave that faces to said object and an opposite concave that faces to said image, a meniscus-shaped positive lens with a convex that faces to said object, which are arranged in this order from said object side to said image side and in said second lens group, each of said object-side surface of said negative lens arranged on said object side and said object-side surface of said positive lens is formed in an aspherical shape and satisfies the following conditional expression (1): 2.0 <f 1/( fw·ft ) 1/2 <2.5 (1) wherein f 1 is a focal length of said first lens group, fw is a focal length in the whole lens system in a wide angle end state, and ft is a focal length in the whole lens system in a telephoto end state.