| 摘要 |
A zoom lens includes first to fourth lens units arranged in order from an object, respectively. The first lens unit is fixed during power-varying and has positive optical power. The second lens unit is movable during power-varying. The third lens unit is movable so as to compensate image-plane fluctuation in accordance with the power-varying. The fourth lens unit is fixed during the power-varying and has positive optical power. The first lens unit includes a first lens subunit having positive optical power, and a second lens subunit having negative optical power, arranged in order from the object, respectively. One of the first and second lens subunits moves upon focus adjustment. Further, the following conditions are satisfied: <?in-line-formulae description="In-line Formulae" end="lead"?>-2.5<f 1 b/f 1 a<-0.6 and 0.2<f 1 /fT<0.8.<?in-line-formulae description="In-line Formulae" end="tail"?> Wherein f 1 , f 1 a, f 1 b, and fT respectively represent the focal lengths of the first lens unit, the first lens subunit, the second lens subunit, and the overall system of the zoom lens at its telephoto end.
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