| 摘要 |
PROBLEM TO BE SOLVED: To make the depth of a variable power image forming optical system ultimately thinner when retracted by using a zoom mechanism having a small number of component elements, being miniaturized and simplified and having a high image forming performance. SOLUTION: The variable power image forming optical system is composed of a negative first group G1, a positive second group G2, a positive third group G3 and a positive group G4. The distances between individual lens groups are variable when the power is varied and the third group G3 serves as a focusing lens group with which the focusing on an object at closer distance is possible by extending the lens group toward the side of the object. The second group G2 is composed of one positive lens element including an aspherical face and one negative lens element and the second group G2 moves on the optical axis united with an aperture diaphragm S when the power is varied and the third group G3 and the fourth group G4 are composed of two or smaller number of lens elements, respectively.
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