Patent ID: 7457049

Claim:
A high magnification zoom lens system including 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 respectively in order from an object side, wherein the third lens group comprises three lens elements respectively having positive, positive, and negative refractive powers in order from the object side, the fourth lens group comprises at least two positive lens elements and a doublet lens and has a positive refractive power as a whole, each lens group moves independently during magnification change, and the high magnification zoom lens system satisfies the following conditions, 0.40 < f w f bw < 0.55 ⁢ ⁢ and 0.35 < β 3 , 4 ⁢ ⁢ W β 3 , 4 ⁢ ⁢ T < 0.43 , where f w is the focal length of the overall lens system at the wide-angle position, f bw is the back focal length of the lens system at the wide-angle position, β 3,4w is the combined magnification of the third and fourth lens groups at the wide-angle position, and β 3,4T is the combined magnification ratio of the third and fourth lens groups at the telephoto position.