| 摘要 |
PURPOSE:To obtain a zoom lens which has a high zoom ratio and can be used in combination with each device with respect to system, by changing air gaps among lens groups to vary magnifications and satisfying specific conditions. CONSTITUTION:This afocal zoom lens consists of the first lens group which includes a cemented positive lens consisting of a positive lens and a negative lens and has a positive refracting power, the second lens group which includes a cemented negative lens consisting of a positive lens and a negative lens and has a negative refracting power, the third lens group which includes a cemented positive lens consisting of a negative lens and a positive lens and has a positive refracting power, and the fourth lens group which includes a cemented negative meniscus lens consisting of a negative lens and a positive lens and has a negative refracting power, and these lens groups are arranged in order from the object side. Focal lengths fI-fIV of lens groups, average values nu1T-nu4T of Abbe's numbers of positive lenses, and average values nu10-nu40 of Abbe's numbers of negative lenses are so selected that conditions of formulas (1)-(7) are satisfied.
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