Patent ID: 7924509
Filing Date: 2011-04-12
Classification: G02B

Abstract:
1. A variable focal length lens system comprising: a first lens group with a positive refractive power; a second lens group with a negative refractive power; a third lens group with a positive refractive power; and a fourth lens group with a positive refractive power, wherein the first to fourth lens groups are arranged in this order from an object side to an image side, when the position of a lens is changed from a wide-angle end to a telephoto end, a gap between the first lens group and the second lens group increases, a gap between the second lens group and the third lens group decreases, and a gap between the third lens group and the fourth lens group is changed, when the position of the lens is changed from the wide-angle end to the telephoto end, all of the lens groups are moved, an aperture diaphragm is arranged in the vicinity of the third lens group, the fourth lens group is moved during close-distance focusing, the second lens group includes a negative lens having a concave surface facing an image side and a cemented lens of a negative lens having a concave surface facing the image side and a meniscus-shaped positive lens having a convex surface facing the object side arranged in this order from the object side to the image side, a surface, which is closest to the object side, of the negative lens arranged on the object side in the second lens group and a surface of the cemented lens closest to the image side are aspheric surfaces, and the variable focal length lens system satisfies the following Conditional expressions 1 and 2: (where fw indicates the focal length of the entire lens system at the wide-angle end, R