| 摘要 |
PURPOSE:To reduce the size of a telephoto zoom lens and to hold aberrations excellent by moving three groups along an optical axis for power variation while, specially, the 2nd and the 3rd groups are put in partial charge of power variation effect at the same time so as to make an increase in power, and satisfying specific conditions. CONSTITUTION:This telephoto zoom lens consists of the 1st group I which has positive refracting power, the 2nd group II which has negative refracting power, and the 3rd group III which consists of a front group IIIa with positive refracting power and a rear group III with negative refracting power and has positive refracting power on the whole successively from the object side. When the 3rd group is moved along the optical axis for zooming, the 2nd group II and the 3rd group III are moved along the optical axis and then the both are put in partial charge of power variation effect at the same time so as to increase the power, and the requirements shown by inequalities I-IV are met at the same time. The 2nd group II and the 3rd group III are moved from the wide-angle end of the telephoto end so as to increase the power, so the overall length of the lens system is shortened extremely at the wide-angle end and the aberrations are held excellent.
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