| 摘要 |
PURPOSE:To improve depiction performance by composing a telephoto lens system of the 1st positive, the 2nd negative, the 3rd negative or positive, and the 4th positive lens groups and performing focusing by moving the 2nd and the 3rd lens, and allowing the telephoto lens system to meet specific requirements. CONSTITUTION:The telephoto lens system consists of the 1st lens group with positive power, the 2nd lens group with negative power, the 3rd lens group with negative or positive power, and the 4th lens group with positive power successively from the object side and the 2nd and the 3rd lens groups are moved to perform focusing operation. This telephoto lens system meets requirements, e.g. -2.5<f/f2.3<-0.9, -0.25<f2/f3<0.90, 0.40<X3/X2<1.00, and 0.05<d2-3/f<0.15, and 0.10<d3-4/f<0.18. Here, (f) is the focal length of the whole system when the system is focused on an infinite-distance body, f2.3 the composite focal length of the 2nd and the 3rd lens groups when the system is focused on the infinite-distance body, fi the foal length of the (i)th lens group, Xi the movement quantity of the (i)th lens group, and Di-j the air gap between the (i)th lens group and the (j)th lens group.
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