| 摘要 |
PURPOSE:To make a lens system small-sized and low-cost and enhance the performance and increase the variable power ratio by setting specific conditional inequalities between focal lengths and radii of curvature in a lens system consisting of a first group of four lenses with positive focal lengths and a second group with negative focal lengths. CONSTITUTION:The lens system consists of the first group which consists of four lenses, namely, a positive meniscus lens whose object side is made convex, two negative lenses, and a positive lens and has a positive focal length and the second group which consists of a negative meniscus lens and has a negative focal length, and eight specific conditional inequalities are set between focal lengths (f) and radii (r) of curvature. Extents of movement and powers of lenses in the first and second groups for variable power are controlled by inequalities I and II, and the spherical aberration, the astigmatism, and the chromatic aberration are compensated by inequalities III and IV, and the Petzval..s sum of the first group is compensated by the formula V. the chromatic aberation of the first and second groups is compensated by inequalities VI and VIII, and the power is varied while keeping the distance between the object surface and the focal surface constant by the inequality VII. Thus, the lens system consists of a small number of lenses to make the lens system small-sized and low-cost, and the variable power ratio is increased and the capacity is improved.
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