| CPC G02B 13/0045 (2013.01) [G02B 9/60 (2013.01); G02B 13/008 (2013.01)] | 12 Claims |

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1. An optical imaging system comprising:
a first lens having a positive refractive power;
a second lens having a concave image-side surface in an optical axis region;
a third lens having a concave object-side surface in an optical axis region and a concave image-side surface in an optical axis region;
a fourth lens having a positive refractive power; and
a fifth lens having a refractive power,
wherein the first to fifth lenses are sequentially disposed in ascending numerical order along an optical axis from an object side of the optical imaging system toward an imaging plane of the optical imaging system,
wherein a radius of curvature of an image-side surface of the fourth lens is greater than a radius of curvature of an object-side surface of the fourth lens,
wherein a thickness along an optical axis of the first lens is greater than a thickness along an optical axis of the fifth lens, and
wherein 5.0<(t1+t2)/t3<12.0, where t1 is the thickness along the optical axis of the first lens, t2 is a thickness along the optical axis of the second lens, and t3 is a thickness along the optical axis of the third lens.
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