Patent ID: 7385766

Claim:
A variable focal length lens system comprising: a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, a fourth lens group having a positive refractive power, and a fifth lens group arranged in this order from an object side to an image plane side; wherein, when a lens zoom position is changed from a wide-angle position at which a focal length of the variable focal length lens system is the shortest to a telephoto position at which the focal length is the longest, at least the first to fourth lens groups are movable and the second lens group is moved towards the image plane side and the third lens group is moved towards the object side so that a distance between the first lens group and the second lens group increases and a distance between the second lens group and the third lens group decreases, and the fourth lens group is moved along an optical axis direction so as to compensate for the change in the position of the image plane caused by the movement of each lens group, and wherein the fifth lens group includes a negative subgroup having a negative refractive power and a positive subgroup disposed on the image plane side of the negative subgroup and having a positive refractive power, and wherein the following conditional expression (1) is satisfied: 0.5<(β2 t/β 2 w )/ Z< 0.85 (1) where β 2 t =the lateral magnification of the second lens group at the telephoto position, β 2 w =the lateral magnification of the second lens group at the wide-angle position, and Z=a zoom ratio.