| 摘要 |
PROBLEM TO BE SOLVED: To obtain a four-group zoom lens having high optical performance over entire variable power range by satisfying a specified condition at a variator (a second group) for variable power. SOLUTION: The second group V has the second A group VA of negative refracting power and the second B group VB of positive refracting power, and both groups are moved to the side of an image surface at different speed at the time of variable power from a wide angle end to a telephoto end. The expressions of 1.05<FN1, FN1=f1/(fT/FNT), 3.4<|f2B/f2A|<10.5, 1<β2B, 0<β3<1, 0.37<β2BXβ3<0.73, -0.044<(R2Bb+R2Ba)/(R2Bb-R2Ba) are satisfied. In the expressions, fT and FNT mean the focal distances and the F number of the entire systems of a telephoto end, and f2A and f2B mean the focal distance of the second A group VA and the second B group VB, andβ2B andβ3 mean the lateral magnifications of the second B group VB and a third group C at the wide angle end and R2Ba and R2Bb mean the radiuses of curvature of lens surfaces on the sides of the object and the image surface. Also, the interval of principal points between the second A group VA and the second B group VB is appropriately set.
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