| 摘要 |
A zoom optical system includes first through fourth lens groups having negative-positive-negative-positive optical powers. Assuming that a curvature radius of an object-side lens surface of a negative lens element in the first lens group is r1, a curvature radius of an image-side lens surface of the negative lens element in the first lens group is r2, a focal length of the third lens group is f3, a focal length of the entirety of the optical system at the wide angle end is fw, a focal length of the entirety of the optical system at the telephoto end is ft, and an average refractive index of positive lens elements in the second lens group is nd2p, the zoom optical system satisfies the conditional expressions: <?in-line-formulae description="In-line Formulae" end="lead"?>0<(r1+r2)/(r1-r2)<1.0<?in-line-formulae description="In-line Formulae" end="tail"?> <?in-line-formulae description="In-line Formulae" end="lead"?>-0.9<f3/√{square root over ((fwxft)<-0.4<?in-line-formulae description="In-line Formulae" end="tail"?> <?in-line-formulae description="In-line Formulae" end="lead"?>1.6<ndp2<?in-line-formulae description="In-line Formulae" end="tail"?>
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