| CPC G02B 13/0045 (2013.01) [G02B 9/60 (2013.01)] | 18 Claims |

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1. An optical imaging system comprising:
a first lens, a second lens, a third lens, a fourth lens, and a fifth lens sequentially disposed in ascending numerical order along an optical axis of the optical imaging system from an object side of the optical imaging system toward an imaging plane of the optical imaging system,
wherein the first lens has a positive refractive power and a convex image-side surface in a paraxial region,
wherein the second lens has a negative refractive power,
wherein the third lens has a positive refractive power,
wherein the fourth lens has a negative refractive power, and
wherein LfS2el/L1S1el≤0.65 and 0.05<T1/TTL<0.1 are satisfied, where LfS2el is a maximum effective radius of an image-side surface of the fifth lens, L1S1el is a maximum effective radius of an object-side surface of the first lens, T1 is a thickness of the first lens along the optical axis, and TTL is a distance along the optical axis from the object-side surface of the first lens to the imaging plane, and
wherein 0.8≤TTL/f≤0.95 is satisfied, where f is an overall focal length of the optical imaging system.
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