| 摘要 |
PROBLEM TO BE SOLVED: To obtain a zoom lens which is provided with four lens groups as a whole and constituted so that the focusing is executed by the lens group arranged behind a variable power system and the whole of a lens system is made compact and whose variable power ratio is >=20. SOLUTION: This zoom lens is provided with a 1st group L1 whose refractive power is positive, a 2nd group L2 whose refractive power is negative, a 3rd group L3 whose refractive power is positive and the 4th group L4 whose refractive power is positive in turn from an object side. By moving the group L2 to an image surface side, a variable power action is executed to a telephoto end from a wide angle end. Then, the fluctuation of an image surface occurring in accordance with the variable power action is corrected by moving the group L4. Besides, the focusing action is exectued by moving the 4th group L4. Thus, the lens constitution of the respecive lens groups are made proper.
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