Patent ID: 7920333
Filing Date: 2011-04-05
Classification: G02B

Abstract:
1. A variable focal distance lens system comprising: a first lens group having positive refractive power; a second lens group having negative refractive power; a third lens group having positive refractive power; and a fourth lens group having positive refractive power, wherein the first to fourth lens groups are sequentially disposed from an object side to an image side, wherein, during a change in positional state of lenses from a wide-angle end state to a telescopic end state, the interval between the first and second lens groups is increased, the interval between the second and third lens groups is reduced, and the interval between the third and fourth lens groups is changed, wherein, during the change in positional state of the lenses from the wide-angle end state to the telescopic end state, all lens groups are movable, wherein the second lens group is configured to include a negative lens having a concave surface facing the image side, and a cemented lens formed by 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, which are sequentially disposed from the object side to the image side, wherein the third lens group is configured to include a cemented lens formed by a positive lens having a convex surface facing the object side and a negative lens having a concave surface facing the image side, and a positive lens having two convex surfaces, which are sequentially disposed from the object side to the image side, wherein, in the second lens group, each of two surfaces of the negative lens disposed on the object side and the most image-side surface of the cemented lens is formed into an aspherical surface, wherein the variable focal distance lens system satisfies the following conditional expressions (1) and (2): (1) −0.65<(R33−R34)/(R33+R34)<−0.25 and (2) −1.0<(R22−R23)/(R22+R23)<−0.6, and wherein R33 represents the radius of curvature of the most image-side surface of the cemented lens of the third lens group, R34 represents the radius of curvature of the object-side surface of the positive lens of the third lens group disposed on the most image side, R22 represents the radius of curvature of the image-side surface of the negative lens of the second lens group disposed on the most object side, and R23 represents the radius of curvature of the most object-side surface of the cemented lens of the second lens group.