Patent ID: 7933074
Filing Date: 2011-04-26
Classification: G02B

Abstract:
1. A zoom lens unit, comprising in order from an object side to an image side: a first lens group having a positive refracting power; a second lens group having a negative refracting power; a third lens group having a positive refracting power; and a fourth lens group having a positive refracting power, an aperture stop being disposed on an object side of the third lens group, and when changing magnification from a wide-angle end to a telephoto end, all the lens groups are moved, and an interval between the first lens group and the second lens group increases, an interval between the second lens group and the third lens group decreases, and an interval between the third lens group and the fourth lens group increases, wherein the third lens group has at least two positive lenses and one negative lens, and wherein all the positive lenses of the third lens group satisfy the following formula: where, ν d3p represents an Abbe number of each of the positive lenses of the third lens group, and θ gF3p represents a partial dispersion ratio of each of the positive lenses of the third lens group which is defined by the formula: θ gF3p =(n g −n F )/(n F −n C ), n g , n F and n C representing refractive indexes for g line, F line and C line, respectively.