| 摘要 |
PROBLEM TO BE SOLVED: To provide a large-aperture zoom lens having a high variable power ratio, performing focusing by a lens group other than a lens group nearest to an object side, made light in weight, restraining focus movement by variable power to be little and realizing the simplification of the constitution of a lens barrel. SOLUTION: The zoom lens has negative, positive, negative and positive lens groups G1 to G4 from an object side. In the case of variable power from a wide angle end to a telephoto end, space between the 1st group G1 and the 2nd group G2 is decreased, space between the 2nd group G2 and the 3rd group G3 is increased, and space between the 3rd group G3 and the 4th group G4 is decreased. The 2nd group G2 is constituted of a positive front group 2a and a positive rear group 2b from the object side, and performs focusing by moving the front group 2a. The lens groups from the 1st group G1 to the rear group 2b form an almost afocal system at least a part of a focal distance from the wide angle end to the telephoto end, and at least either surface of the lens nearest to the object side in the front group 2a is an aspherical surface where positive refractive power gets weaker and weaker as the surface of the lens is separated from an optical axis or the lens nearest to the object side in the front group 2a is a doublet which is set so that the refractive index of the lens on the object side is smaller than that of the lens on the image side and its bonded surface is concave to the object side. The zoom lens satisfies a prescribed conditional expression. COPYRIGHT: (C)2005,JPO&NCIPI
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