| 摘要 |
A zoom lens is disclosed, comprising, from front to rear, a first lens unit of positive refractive power, a second lens unit of negative refractive power, a third lens unit of positive reactive power and a fourth lens unit of positive refractive power, an aperture stop being positioned between the second and third lens units, the second and fourth lens unit being axially moved to effect zooming and the fourth lens unit being axially moved to effect focusing, wherein particular rules of design are set fourth for the third and fourth lens units to insure that the back focal distance is long enough to contain a color separation prism, and wherein the zoom ratio takes a high value.
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