an image lens system includes a first lens group that includes a first and a second lens , a movable second lens group that includes a third and a fourth lens , and a third lens group that includes a fifth lens . the image lens system satisfies the formulas : 2 . 1 ≦ lw /& lt ; 2 . 5 ; 1 . 9 ≦| fp |/ f 1 |≦ 2 . 2 ; and 0 . 6 ≦| fp 2 / f 2 |≦ 0 . 7 , where “ lw ” represents the overall length of the image lens system in the wide angle state , “ a ” represents the ratio of the effective focal length of the image lens system in the telephoto state to that in the wide angle state , “ y ” represents the maximum height of image that the image lens system generates , “ fp 1 ” and “ fp 2 ” represents the effective focal lengths of the second and the fourth lenses , “ f 1 ” and “ f 2 ” represents the effective focal lengths of the first and the second lens groups .