Patent ID: 8270095
Filing Date: 2012-09-18
Classification: G02B

Abstract:
1. A variable-power optical system comprising, in order from an object side thereof: a first lens group with a negative optical power; a second lens group with a positive optical power; a third lens group with a negative optical power; and a fourth lens group with a positive optical power, wherein an interval between the first lens group and the second lens group decreases when a power of the variable-power optical system varies from a wide-angle end to a telephoto end, the first lens group comprises a meniscus lens with a positive optical power including a convex surface facing the object side, the second lens group includes at least one aspheric surface, the variable-power optical system further comprising an aperture stop arranged on the object side of the second lens group, an aperture diameter of the aperture stop being fixed, and the variable-power optical system satisfies the following expressions (1) through (4): where T1 is an axial thickness from a front lens surface of the first lens group to a rear lens surface of the first lens group, fw is a composite focal length of a total optical system of the variable-power optical system at the wide-angle end, ft is a composite focal length of the total optical system at the telephoto end, ΔN2 is a difference between a mean refractive index of a positive lens or lenses and a mean refractive index of a negative lens or lenses, among lenses in the second lens group, Δv 2 is a difference between a mean Abbe number of a positive lens or lenses and a mean Abbe number of a negative lens or lenses, among lenses in the second lens group, N1 is a maximum value of refractive indices of lenses in the first lens group; and N1p is a refractive index of the meniscus lens in the first lens group.