| CPC G02B 13/0045 (2013.01) [G02B 9/64 (2013.01)] | 20 Claims |

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1. An imaging optical system, comprising:
a first lens of a negative refractive power having a concave image-side surface;
a second lens of a negative refractive power having a concave image-side surface;
a third lens of a positive refractive power having a concave image-side surface;
a fourth lens of a positive refractive power having a convex image-side surface;
a fifth lens of a positive refractive power having a concave object-side surface and a convex image-side surface;
a sixth lens of a negative refractive power having a concave object-side surface and a convex image-side surface;
a seventh lens having a convex image-side surface and an object-side surface, the object-side surface of the seventh lens being an aspherical surface having a convex center portion and at least one inflection point at a periphery of the convex center portion; and
an eighth lens having a concave object-side surface and an image-side surface, the image-side surface of the eighth lens being an aspherical surface having a concave center portion and at least one inflection point at a periphery of the concave center portion;
wherein the first lens, the second lens, the third lens, the fourth lens, the fifth lens, the sixth lens, the seventh lens and the eighth lens are arranged in order in a direction from an object side to an image side; and
wherein the imaging optical system satisfies:
|f1/f2|<6;
|f12/f3|<0.5;
0<T67/T34<1.0;
where f1 represents a focal length of the first lens, f2 represents a focal length of the second lens, f3 represents a focal length of the third lens, f12 represents a combined focal length of the first lens and the second lens, T34 represents a distance along an optical axis from the image-side surface of the third lens to an object-side surface of the fourth lens, and T67 represents a distance along the optical axis from the image-side surface of the sixth lens to the object-side surface of the seventh lens.
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