Patent ID: 6178049
Filing Date: 2001-01-23
Classification: G02B

Abstract:
A zoom lens comprising, in order from an object side to an image side, a first lens unit of positive refractive power, a second lens unit of negative refractive power, a third lens unit of positive refractive power, and a fourth lens unit of positive refractive power, the second lens unit being moved toward the image side to vary magnification from a wide-angle end to a telephoto end, and the fourth lens unit being moved, while depicting a locus convex toward the object side, to compensate for an image shift caused by variation of magnification, wherein said fourth lens unit consists of, in order from the object side to the image side, a positive first lens, a negative second lens, and a positive third lens, and said fourth lens unit has at least one aspheric surface, and wherein, letting a focal length of said third lens unit be denoted by f.sub.3, letting focal lengths at the wide-angle end and at the telephoto end of said zoom lens be denoted by f.sub.W and f.sub.T, respectively, and letting an F-number at the wide-angle end of said zoom lens be denoted by F.sub.NW, and lettingf.sub.M =f.sub.W.multidot.f.sub.T,the following condition is satisfied:3.44<f.sub.3.times.F.sub.NW /f.sub.M <15.38,wherein said third lens unit has, in order from the object side to the image side, a negative first lens, a positive second lens of meniscus form convex toward the image side, and at least one cemented lens.