Optical system

1. An optical system comprising:

a first lens having positive refractive power;

a second lens having negative refractive power and a convex object-side surface;

a third lens having positive refractive power and a convex image-side surface;

a fourth lens having negative refractive power;

a fifth lens having refractive power and a concave image-side surface in the paraxial region;

a sixth lens having refractive power and a convex object-side surface; and

wherein the first to sixth lenses are sequentially disposed from an object side, and

wherein an overall focal length of the optical system f and a focal length of the fifth lens f5 satisfy:

0.2<| f/f 5|<0.4, and

wherein the focal length of the fifth lens f5 and a focal length of the sixth lens f6 satisfy:

0.3<| f/f 5|+| f/f 6|<0.6.

2. The optical system of claim 1 , wherein a distance from an object-side surface of the first lens to an imaging surface of an image sensor TTL and the overall focal length of the optical system f satisfy:

1.1<TTL/ f< 1.35.

3. The optical system of claim 1 , wherein a radius of curvature of an object-side surface of the fifth lens r9 and the overall focal length of the optical system f satisfy:

1.0<∥ r 9|/ f< 40.

4. The optical system of claim 1 , wherein an Abbe number of the fifth lens v5 and an Abbe number of the sixth lens v6 satisfy:

| v 5− v 6|>20.

5. The optical system of claim 1 , wherein an Abbe number of the first lens v1 and an Abbe number of the second lens v2 satisfy:

v 1− v 2>20.

6. The optical system of claim 1 , wherein a focal length of the first lens f1 and the overall focal length of the optical system f satisfy:

1.3 <f/f 1<1.6.

7. The optical system of claim 1 , wherein the overall focal length of the optical system f and a focal length of the third lens f3 satisfy:

0.1< f/f 3<0.3.

8. The optical system of claim 1 , wherein a focal length of the first lens f1 and a focal length of the third lens f3 satisfy:

0< f 1/ f 3<0.2.

9. The optical system of claim 1 , wherein a focal length of the first lens f1 and a focal length of the second lens f2 satisfy:

2<| f/f 1|+| f/f 2|<2.5.

10. The optical system of claim 1 , wherein a focal length of the third lens f3 and a focal length of the fourth lens f4 satisfy:

0.1<| f/f 3|+| f/f 4|<0.4.

11. The optical system of claim 1 , wherein a distance from the object-side surface of the first lens to an imaging surface of an image sensor TTL and a diagonal length of the imaging surface of the image sensor ImgH satisfy:

1.5<TTL/ImgH<1.7.

12. The optical system of claim 1 , wherein a field of view of the optical system is between 65° and 80°.

13. The optical system of claim 1 , wherein an object-side surface of the first lens is convex.

14. The optical system of claim 1 , wherein an image-side surface of the first lens is convex.

15. The optical system of claim 1 , wherein an image-side surface of the second lens is concave.

16. The optical system of claim 1 , wherein an object-side surface of the third lens is concave.

17. The optical system of claim 1 , wherein an object-side surface of the fourth lens is concave.

18. The optical system of claim 1 , wherein an image-side surface of the fourth lens is convex.

19. The optical system of claim 1 , wherein the refractive power of the fifth lens is negative.

20. The optical system of claim 1 , wherein an object-side surface of the fifth lens is concave.

21. The optical system of claim 1 , wherein at least one or more inflection points are formed on at least one or both of an object-side surface and the image-side surface of the fifth lens.

22. The optical system of claim 1 , wherein the refractive power of the sixth lens is positive.

23. The optical system of claim 1 , wherein an image-side surface of the sixth lens is concave.

24. The optical system of claim 1 , wherein at least one or more inflection points on at least one or both of an object-side surface and an image-side surface of the sixth lens.

25. The optical system of claim 1 , wherein at least one or both of an object-side surface and an image-side surface of each of the first to sixth lenses is aspherical.

26. An optical system comprising:

a first lens having positive refractive power;

a second lens having negative refractive power and a convex object-side surface;

a third lens having positive refractive power and a convex image-side surface;

a fourth lens having negative refractive power;

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

a sixth lens having refractive power,

wherein the first to sixth lenses are sequentially disposed from an object side, and

wherein an Abbe number of the first lens v1 and an Abbe number of the second lens v2 satisfy:

v 1− v 2>20, and

wherein an overall focal length of the optical system f, a focal length of the fifth lens f5 and a focal length of the sixth lens f6 satisfy:

0.3<| f/f 5|+| f/f 6|<0.6.

27. An optical system comprising:

a stop; and

first, second, third, fourth, fifth, and sixth lenses disposed sequentially from an object side, wherein

the first lens has positive refractive power,

the second lens has negative refractive power and a convex object-side surface,

the third lens has positive refractive power,

the fourth lens has negative refractive power,

the fifth lens has concave image-side surface,

the sixth lens has a convex object-side surface, and

a radius of the stop SD and an overall focal length of the optical system f satisfy:

0.2<SD/ f< 0.6, and

wherein a focal length of the fifth lens f5, and a focal length of the sixth lens f6, satisfy:

0.3<| f/f 5|+| f/f 6|<0.6.

28. The optical system of claim 27 , wherein an image-side surface of the third lens is convex.

29. The optical system of claim 27 , wherein the fifth lens has negative refractive power, and the sixth lens has positive refractive power.

30. The optical system of claim 27 , wherein a distance from an object-side surface of the first lens to an imaging surface of an image sensor TTL and an overall focal length of the optical system f satisfy:

1.1<TTL/ f< 1.35.