Patent ID: 6982836

Claim:
A zoom lens system comprises a positive first lens group, a negative second lens group, a positive third lens group, and a positive fourth lens group, in this order from an object, wherein upon zooming from the short focal length extremity to the long focal length extremity, said negative second lens group is arranged to move from the object side to the image side, and said positive fourth lens group is arranged to move in order to compensate the move of the image plane that occurs upon zooming; wherein said positive fourth lens group comprises a first sub-lens group comprising a positive lens element, and a second sub-lens group comprising cemented lens elements comprising a negative lens element and a positive lens element, in this order from the object; wherein said first sub-lens group comprises an aspherical surface on at least the object-side surface thereof, and said aspherical surface is formed so that the higher a height from the optical axis in a radial direction becomes the weaker the refractive power is, compared with a paraxial spherical surface; and wherein said first sub-lens group satisfies the following conditions: 0.55 <f 4 a/f 4 b <−0.07 0.15 <d 4 ab/f 4 <−0.50 wherein f 4 a designates the focal length of said first sub-lens group of said positive fourth lens group; f 4 b designates the focal length of said second sub-lens group of said positive fourth lens group; d 4 ab designates the distance between said first sub-lens group and said second sub-lens group of said positive fourth lens group; and f 4 designates the focal length of said positive fourth lens group.