Optical imaging system

1. An optical imaging system comprising:

a first lens having positive refractive power and a concave image-side surface;

a second lens having negative refractive power and a concave image-side surface;

a third lens having a refractive power;

a fourth lens having a refractive power;

a fifth lens having positive refractive power;

a sixth lens having a refractive power;

a seventh lens having a refractive power; and

an eighth lens having a refractive power,

wherein the first to eighth lenses are sequentially disposed in 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, and

wherein a radius of curvature of an object-side surface of the second lens is greater than a radius of curvature of an image-side surface of the first lens.

2. The optical imaging system of claim 1 , the third lens has a convex object-side surface.

3. The optical imaging system of claim 1 , the fourth lens has a convex object-side surface.

4. The optical imaging system of claim 1 , the fifth lens has a convex image-side surface.

5. The optical imaging system of claim 1 , the seventh lens has positive refractive power.

6. The optical imaging system of claim 1 , the eighth lens has negative refractive power.

7. An optical imaging system comprising:

a first lens having a refractive power;

a second lens having a refractive power;

a third lens having a refractive power;

a fourth lens having a refractive power;

a fifth lens having a refractive power;

a sixth lens having a refractive power;

a seventh lens having a refractive power; and

an eighth lens having a refractive power,

wherein the first to eighth lenses are sequentially disposed in 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 optical imaging system satisfies 1.0<TTL/f1<1.4 and 50<(V5+V6+V7+V8)/4,

where TTL is a distance along the optical axis from an object-side surface of the first lens to an imaging plane, f1 is a focal length of the first lens, V5 is an Abbe number of the fifth lens, V6 is an Abbe number of the sixth lens, V7 is an Abbe number of the seventh lens, and V8 is an Abbe number of the eighth lens.

8. The optical imaging system of claim 7 , wherein the optical imaging system satisfies Nd6<1.6, where Nd6 is a refractive index of the sixth lens.

9. The optical imaging system of claim 7 , wherein the optical imaging system satisfies 2.0<|R15/R16|<5.0, where R15 is a radius of curvature of an object-side surface of the eighth lens, and R16 is a radius of curvature of an image-side surface of the eighth lens.

10. The optical imaging system of claim 7 , wherein a radius of curvature of an object-side surface of the third lens is greater than a radius of curvature of an image-side surface of the second lens.

11. The optical imaging system of claim 7 , wherein a radius of curvature of an object-side surface of the second lens is greater than a radius of curvature of an image-side surface of the first lens.

12. The optical imaging system of claim 7 , the fourth lens has a convex object-side surface.

13. The optical imaging system of claim 7 , the fifth lens has positive refractive power.

14. The optical imaging system of claim 7 , the seventh lens has positive refractive power.