Patent ID: 8194329
Filing Date: 2012-06-05
Classification: G02B

Abstract:
1. A variable magnification optical system comprising: a first lens group having negative refractive power; an aperture stop; and a second lens group having positive refractive power, which are arranged from the object side of the variable magnification optical system, wherein the magnification of the variable magnification optical system is changed by changing an interval between the first lens group and the second lens group in the direction of an optical axis, and the position of an image plane is corrected by moving the first lens group in the direction of the optical axis when correction of the position of the image plane becomes necessary by changing the magnification, and wherein a negative lens having a concave surface facing the image side of the variable magnification optical system is arranged on the most object side of the first lens group, and an aspheric lens having a concave surface facing the object side and an aspheric surface facing the image side is arranged on the most image side of the first lens group, and a positive lens having a convex surface facing the image side is arranged, on the object side of the aspheric lens, immediately before the aspheric lens, and wherein the image-side surface of the aspheric lens includes a portion having higher positive power on the outside of positions through which outermost rays of an axial beam pass, compared with power in a region of the surface of the aspheric lens in the vicinity of the optical axis.