Patent ID: 7362510
Filing Date: 2008-04-22
Classification: G02B

Abstract:
1. A zoom lens wherein a first lens group having a positive refractive power and having a fixed position, a second lens group of the variable magnification type having a negative refractive power and having a position movable for magnification variation, a third lens group having a positive refractive power and having a fixed position and a fourth lens group having a positive refractive power and having a position variable for adjustment of a focal position upon magnification variation and upon focusing are disposed in order from an object side, wherein: said first lens group includes a cemented lens of a first lens in the form of a concave lens and a second lens in the form of a convex lens and a third lens in the form of a convex meniscus lens having a convex face directed to the object side, disposed in order from the object side; said second lens group includes a fourth lens in the form of a concave lens and a cemented lens of a fifth lens in the form of a biconcave lens and a sixth lens in the form of a convex lens, disposed in order from the object side; said third lens group includes a two-element or three-element cemented lens including a seventh lens in the form of a biconvex lens positioned nearest to the object side and an eighth lens in the form of a concave lens bonded to said seventh lens; said fourth lens group includes a cemented lens of a concave lens having a concave face directed to the object side and a convex lens and a biconvex lens, and at least one face of the two convex lenses in said fourth lens group is formed from an aspheric face; and the following conditional expressions (1), (2), (3), (4), (5) and (6) are satisfied: where fw: focal distance of the entire system at the wide-angle end state fIII: focal distance of said third lens group fIV: focal distance of said fourth lens group HIV′: image side principal point of said fourth lens group φ v IV: equivalent Abbe number where it is assumed that said fourth lens group is a thin closely contacting type lens group (where 1/v IV=fIV{l/(f v III: equivalent Abbe number where it is assumed that said third lens group is a thin closely contacting lens group (where 1/v III=fIII{l/(f