High magnification zoom lens

摘要

A high magnification zoom lens system includes a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a fourth lens group having positive refractive power, which are arranged in order from an object side. The third lens group includes three lens elements respectively having positive, positive, and negative refractive powers in order from the object side. The fourth lens group includes at least two positive lens elements and a doublet lens having positive refractive power as a whole, each lens group moves independently during magnification change. The high magnification zoom lens system satisfies the conditions that $0.40<\frac{f_w}{f_{\mathrm{bw}}}<0.55\mathrm{and}0.35<\frac{{\mathrm{beta}}_{3,4W}}{{\mathrm{beta}}_{3,4T}}<0.43,$ where f_w is the focal length of the overall lens system at a wide-angle end, f_bw is the back focal length of the lens system at the wide-angle position, beta_3,4w is the combined magnification ratio of the third and fourth lens groups at the wide-angle position, and beta_3,4T is the combined magnification ratio of the third and fourth lens groups at the telephoto position.