| 摘要 |
PURPOSE:To expand a wide angle range, to make the titled lens system compact, to reduce the cost of the lens system, and to increase its zoom ratio by constituting the lens system of the 1st movable group consisting of three lenses and the 2nd movable group consisting of five lenses and satisfying the lens system with specific conditions. CONSTITUTION:The lens system is constituted of the 1st movable lens group consisting of a negative meniscus lens L1 turning its convex surface to the object side, a lens L2 having concave surfaces on both the sides, a lens L3 having convex surfaces on both the sides arranged successively from the object side and the 2nd movable lens group consisting of a lens L4 having convex surfaces on both the sides, a positive meniscus lens L5 turning its convex surface to the object side, a positive meniscus lens L6 turning its convex surface to the object side, a negative lens L7, and a positive lens L8 arranged successively from the object side and the lens system is satisfied with the conditions of inequalities. In the inequalities, fI and fII are focal distances of the 1st and 2nd groups, f1 and f7 are focal distances of the lenses L1, L7 and fw is the shortest focal distance. The inequality (1) gives a condition of proper power arrangement of the 1st and 2nd groups, the inequality (2) is the proper range of the focal distance of the negative lens L1 and the inequality (3) is the proper range of the focal distance of the negative lens L7.
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