Patent ID: 7715113

Claim:
A zoom lens comprising, in order from an object side: 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; and a fourth lens group having a positive refractive power, wherein the first lens group and the third lens group are fixed during zooming, the second lens group is moved during the zooming, the fourth lens group is moved during zooming and during focusing, the fourth lens group includes, in order from the object side, a single positive lens having aspheric surfaces on both of the object side and an image side, the object-side surface of the single positive lens being convex and having a refractive power stronger than that of the image-side surface of the single positive lens, and a cemented lens having a negative refractive power as a whole, the cemented lens formed of a negative lens and a positive meniscus lens that has a convex surface directed to the object side, the following conditional expressions are satisfied: 0.04 <Da/f 4<0.15 (1) ( n 41 +n 43 )/2<1.53 (2) where Da denotes a gap between the single positive lens and the cemented lens in the fourth lens group, f4 denotes a focal length of the fourth lens group, n 41 denotes a refractive index of the single positive lens in the fourth lens group at the d-line, and n 43 denotes a refractive index of the positive meniscus lens in the fourth lens group at the d-line.