Patent attributes
The present invention is directed to a compact large-aperture-ratio inner-focusing telephoto zoom lens of the reduced total lens extension where minimizing a photo-shooting distance down to as short as 1 meter does not cause the lens optics to displace accordingly greater during the focusing. The large-aperture-ratio inner-focusing telephoto zoom lens has four groups of lens pieces, namely, the 1st lens group of positive refractive power, the 2nd lens group of negative refractive power, the 3rd lens group of positive refractive power, and, the 4th lens group of positive refractive power arranged in series on the basis of “closer to a subject first,” and that has the 2nd and 3rd lens groups moved along the optical axis to vary a magnification power. In such a telephoto zoom lens, the 1st lens group includes the leading subgroup of lens pieces or foremost lens subgroup G1F and the trailing subgroup of lens pieces or rear lens subgroup G1R where the G1F has two of a concave lens piece and a convex lens piece cemented into a single piece of composite lens while the G1R has a composite lens of one concave lens piece and two convex lens pieces in series. The rear lens subgroup G1R in the 1st lens group is moved along the optical axis for the focusing, and the telephoto zoom lens has an optical property that satisfies requirements as follows:1.3<f1/fw<1.9 (1)where f1 is a focal length of the 1st lens group, and fw is a focal length of the telephoto zoom lens in the wide-angle view mode.
