Optical imaging system

1. An optical imaging system comprising:

a first lens comprising a positive refractive power, a second lens comprising a negative refractive power, a third lens comprising a refractive power, a fourth lens comprising a positive refractive power, a fifth lens comprising a negative refractive power, a sixth lens comprising a refractive power, a seventh lens comprising a refractive power, and an eighth lens comprising a refractive power, sequentially disposed from an object side to an imaging plane,

wherein BFL/f<0.15, where BFL represents a distance from an image-side surface of the eighth lens to an imaging plane of an image sensor and f represents an overall focal length of an optical system including the first to eighth lenses.

2. The optical imaging system of claim 1 , wherein 0.7<TTL/f<1.0, where TTL represents a distance from an object-side surface of the first lens to the imaging plane of the image sensor.

3. The optical imaging system of claim 1 , wherein f/ImgH<2.9, where ImgH represents a half of a diagonal length of the imaging plane of the image sensor.

4. The optical imaging system of claim 1 , wherein −30<f 6 /f<30, where f 6 represents a focal length of the sixth lens.

5. The optical imaging system of claim 1 , wherein TTL/ImgH>1.0, where TTL represents a distance from an object-side surface of the first lens to the imaging plane of the image sensor and ImgH represents a half of a diagonal length of the imaging plane of the image sensor.

6. The optical imaging system of claim 1 , further comprising a stop disposed between the third lens and the fourth lens or between the fourth lens and the fifth lens.

7. The optical imaging system of claim 1 , wherein object-side surfaces and image-side surfaces of the first to eighth lenses are aspherical.

8. The optical imaging system of claim 1 , wherein the first lens comprises a convex object-side surface along an optical axis.

9. The optical imaging system of claim 1 , wherein the second lens comprises a convex object-side surface along an optical axis and a concave image-side surface along the optical axis.

10. The optical imaging system of claim 1 , wherein the third lens comprises a convex object-side surface along an optical axis and a concave image-side surface along the optical axis.

11. The optical imaging system of claim 1 , wherein the fourth lens comprises a convex object-side surface along an optical axis and a concave image-side surface along the optical axis.

12. The optical imaging system of claim 1 , wherein the fifth lens comprises a concave image-side surface along an optical axis.

13. The optical imaging system of claim 1 , wherein the sixth lens comprises a concave object-side surface along an optical axis.

14. The optical imaging system of claim 1 , wherein the seventh lens comprises a negative refractive power, a concave object-side surface along an optical axis, and a concave image-side surface along the optical axis.

15. The optical imaging system of claim 1 , wherein the eighth lens comprises a positive refractive power and a convex object-side surface along an optical axis.

16. The optical imaging system of claim 1 , wherein

the first lens, second lens, the third lens, the fourth lens, and the eighth lens each comprise a convex object-side surface,

the second lens, the third lens, the fourth lens, the fifth lens, and the seventh lens each comprise a concave image-side surface, and

the sixth lens and the seventh lens each comprise a concave object-side surface.

17. An optical imaging system comprising:

a first lens comprising a positive refractive power, a second lens comprising a negative refractive power, a third lens comprising a refractive power, a fourth lens comprising a positive refractive power, a fifth lens comprising a negative refractive power, a sixth lens comprising a refractive power, a seventh lens comprising a refractive power, and an eighth lens comprising a refractive power, sequentially disposed from an object side to an imaging plane, and

wherein 0.7<TTL/f<1.0, where TTL represents a distance from an object-side surface of the first lens to an imaging plane of an image sensor and f represents an overall focal length of the optical imaging system.

18. The optical imaging system of claim 17 , wherein

the first lens, second lens, the third lens, the fourth lens, and the eighth lens each comprise a convex object-side surface,

the second lens, the third lens, the fourth lens, the fifth lens, and the seventh lens each comprise a concave image-side surface, and

the sixth lens and the seventh lens each comprise a concave object-side surface.

19. An optical imaging system comprising:

a first lens having a positive refractive power;

a second lens comprising a negative refractive power, a third lens comprising a refractive power, a fourth lens comprising a positive refractive power, a fifth lens comprising a negative refractive power, a sixth lens comprising a refractive power, and a seventh lens comprising a refractive power;

an eighth lens having a refractive power and a convex object-side surface along an optical axis,

wherein the first to eighth lenses are sequentially disposed from an object side to an imaging plane,

wherein an F-number of the optical imaging system is 2.4 or less,

wherein a field of view (FOV) of the optical imaging system is 40° or less, and

wherein 0.7<TTL/f<1.0, where TTL represents a distance from an object-side surface of the first lens to an imaging plane of an image sensor and f represents an overall focal length of the optical imaging system.

20. The optical imaging system of claim 19 , wherein

the first lens, second lens, the third lens, and the fourth lens each comprise a convex object-side surface,

the second lens, the third lens, the fourth lens, the fifth lens, and the seventh lens each comprise a concave image-side surface, and

the sixth lens and the seventh lens each comprise a concave object-side surface.