| 摘要 |
An optical system comprises from the object side: a positive first lens element, a negative second lens element, a positive third lens element, a fourth lens element, and an aperture stop located between the object side of the optical system and the second lens element for controlling the brightness of the optical system. A radius of curvature R 3 of a front surface of the second lens element satisfies the relation: -0.02 [1/mm]<1/R 3 <0.22 [1/mm], an Abbe number V 2 of the second lens element is less than 40. A focal length of the fourth lens element is f 4 , a focal length of the optical system is f, they satisfy the relation: f/f 4 <0.1, at least one inflection point is formed on the rear surface of the fourth lens element.
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