Patent ID: 9638901
Date: 2017-05-02
CPC Classifications: G02B,H04N

Claim:
1. A zoom lens comprising: a first lens group having positive refractive power; a second lens group having negative refractive power; a third lens group having negative refractive power; and a fourth lens group having positive refractive power, the first to fourth lens groups being arranged in an order starting from an object side to an image plane side, wherein in magnification change, the second and third lens groups are moved so that intervals between the first and second lens groups, between the second and third lens groups and between the third and fourth lens groups are changed, the fourth lens group includes, in an order starting from a side closest to an image plane to the object side, a first positive lens, a first negative lens, a second negative lens and a second positive lens, when an Abbe number νd is a value obtained by (nd−1)/(ng−nC) where a refractive index relative to d-line is nd, a refractive index relative to g-line is ng, and a refractive index relative to C-line is nC, in terms of a material that forms the lenses, and when the Abbe number of the first positive lens is νd intervals between lenses in the second lens group are unchanged in the magnification change, the fourth lens group includes two positive lenses on the object side of the second positive lens, when an average value of the Abbe numbers of the three lenses including the second positive lens and the two positive lenses is νd when a partial dispersion ratio θ