| CPC G02B 9/62 (2013.01) [G02B 13/0045 (2013.01); G02B 5/208 (2013.01)] | 20 Claims |

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1. An optical system comprising, in order from an object side to an image side along an optical axis:
a first lens with a negative refractive power;
a second lens with a positive refractive power;
a third lens with a negative refractive power;
a fourth lens with a refractive power;
a fifth lens with a positive refractive power, wherein the fifth lens has an object-side surface which is convex near the optical axis and concave near a periphery of the object-side surface of the fifth lens, the object-side surface of the fifth lens has at least one inflection point;
a sixth lens with a negative refractive power, wherein the sixth lens has an object-side surface which is convex near the optical axis and concave near a periphery of the object-side surface of the sixth lens, and an image-side surface which is concave near the optical axis and convex near a periphery of the image-side surface of the sixth lens, and wherein at least one of the object-side surface and the image-side surface of the sixth lens has at least one inflection point; and
the optical system satisfies the following expression:
−9<f4/|f1|<3.5;
wherein f1 represents an effective focal length of the first lens, f4 represents an effective focal length of the fourth lens, and
wherein an object-side surface and an image-side surface of each of the first lens to the sixth lens are rotationally symmetric.
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