| 摘要 |
A first lens group (G 1 ) fixed with respect to the image plane includes a lens ( 11 ) having a negative refractive power, a lens ( 12 ) having a positive refractive power and a lens ( 13 ) having a positive refractive power. A second lens group (G 2 ) has a negative refractive power as a whole, and causes a zooming action when moved along the optical axis. An aperture stop is fixed with respect to the image plane. A third lens group (G 3 ) includes a lens ( 31 ) having a negative refractive power and a lens ( 32 ) having a positive refractive power, has a positive or negative refractive power as a whole, and is fixed with respect to the direction of the optical axis when zooming and when focusing. A fourth lens group (G 4 ) has a positive refractive power as a whole, and moves along the optical axis such that the image plane, which is displaced by a movement of the second lens group (G 2 ) along the optical axis and by a movement of the object, is maintained at a constant position with respect to a reference plane. Thus, it is possible to realize a compact and high-image quality small zoom lens that is suitable for three-CCDs.
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