| CPC G02B 13/0045 (2013.01) [G02B 9/64 (2013.01)] | 8 Claims |

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1. An optical imaging system comprising ten lens elements, the ten lens elements being, in order from an object side to an image side along an optical path, a first lens element, a second lens element, a third lens element, a fourth lens element, a fifth lens element, a sixth lens element, a seventh lens element, an eighth lens element, a ninth lens element and a tenth lens element, and each of the ten lens elements has an object-side surface facing toward the object side and an image-side surface facing toward the image side;
wherein the optical imaging system further comprises an aperture stop, the first lens element has positive refractive power, the second lens element has negative refractive power, the image-side surface of the second lens element is concave in a paraxial region thereof, the fourth lens element has positive refractive power, the image-side surface of the eighth lens element is concave in a paraxial region thereof and has at least one convex shape in an off-axis region thereof, the ninth lens element has positive refractive power, the tenth lens element has negative refractive power, and at least one of the object-side surface and the image-side surface of the tenth lens element has at least one inflection point; and
wherein an axial distance between the aperture stop and the image-side surface of the tenth lens element is SD, an axial distance between the object-side surface of the first lens element and the image-side surface of the tenth lens element is TD, a curvature radius of the image-side surface of the eighth lens element is R16, a curvature radius of the image-side surface of the ninth lens element is R18, a curvature radius of the object-side surface of the tenth lens element is R19, a focal length of the optical imaging system is f, a focal length of the first lens element is f1, and the following conditions are satisfied:
0.30<SD/TD<1.20;
−5.0<(R18+R19)/(R18−R19)<5.0;
0.15<f/R16<8.0; and
0.20<f/f1<4.0.
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