| 摘要 |
An imaging optical system for cameras comprising a stop, a first lens, a second lens, and a third lens in order from object side to image side. The first lens is convex at the object side, and has positive refractive power and both surfaces of which are aspherical. The second lens is convex at the image side and has negative refractive power. The third lens has a concave surface at its central portion facing the image side and a convex surface at its peripheral portions facing the image side. The imaging optical system satisfies the conditions of the following Inequalities: 0.8 < L 2 Y < 1 0.5 < fl f < 0.86 where L denotes the distance from the stop to the image focal point, 2Y denotes the diagonal length of the effective image surface, f denotes the overall focal distance of the imaging optical system, and f1 denotes the focal distance of the first lens.
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