Optical imaging system

1. An optical imaging system, comprising:

a first lens having a convex object-side surface in a paraxial region thereof;

a second lens having a negative refractive power, a convex object-side surface in a paraxial region thereof, and a refractive index of 1.65 or more;

a third lens having a concave image-side surface in a paraxial region thereof;

a fourth lens having a convex object-side surface in a paraxial region thereof;

a fifth lens having a refractive power;

a sixth lens having a positive refractive power, and having a convex object-side surface in a paraxial region thereof; and

a seventh lens having a convex object-side surface, and having a concave image-side surface in a paraxial region thereof,

wherein the optical imaging system comprises a total of seven lenses with refractive power,

wherein the first lens through the seventh lens are sequentially disposed in ascending numerical order from an object side of the optical imaging system toward an imaging plane of the optical imaging system,

wherein a thickness of the fourth lens is greater than a distance from an image-side surface of the third lens to an object-side surface of the fourth lens,

wherein a distance from an image-side surface of the fourth lens to an object-side surface of the fifth lens is greater than a thickness of the second lens, and

wherein the optical imaging system satisfies the following conditional expression:

−31< V 3− V 4,

where V3 is an Abbe number of the third lens, and V4 is an Abbe number of the fourth lens.

2. The optical imaging system of claim 1 , wherein the first lens has a positive refractive power.

3. The optical imaging system of claim 1 , wherein the third lens has a positive refractive power.

4. The optical imaging system of claim 1 , wherein the fourth lens has a positive refractive power.

5. The optical imaging system of claim 1 , wherein the second lens has a concave image-side surface in a paraxial region thereof.

6. The optical imaging system of claim 1 , wherein the third lens has a convex object-side surface in a paraxial region thereof.

7. The optical imaging system of claim 1 , wherein the sixth lens has a convex image-side surface in a paraxial region thereof.

8. The optical imaging system of claim 1 , wherein the optical imaging system satisfies the following conditional expression:

−1.0<( R 11+ R 12)/( R 11− R 12)<1.0

where R11 is a radius of curvature of the object-side surface of the sixth lens, and R12 is a radius of curvature of an image-side surface of the sixth lens.

9. The optical imaging system of claim 1 , wherein the optical imaging system satisfies the following conditional expression:

−1.0<( R 9− R 10)/( R 9+ R 10)<1.0

where R9 is a radius of curvature of an object-side surface of the fifth lens, and R10 is a radius of curvature of an image-side surface of the fifth lens.

10. The optical imaging system of claim 1 , wherein the optical imaging system satisfies the following conditional expression:

35< V 1− V 2

where V1 is an Abbe number of the first lens, and V2 is an Abbe number of the second lens.

11. The optical imaging system of claim 1 , wherein there is an inflection point on either one or both of the object-side surface of the sixth lens and an image-side surface of the sixth lens.

12. The optical imaging system of claim 1 , wherein there is an inflection point on either one or both of an object-side surface of the seventh lens and the image-side surface of the seventh lens.

13. The optical imaging system of claim 1 , wherein the fifth lens has a positive refractive power.

14. An optical imaging system, comprising:

a first lens having a convex object-side surface in a paraxial region thereof;

a second lens having a negative refractive power, a concave image-side surface in a paraxial region thereof, and a refractive index of 1.65 or more;

a third lens having a refractive power;

a fourth lens having a convex object-side surface in a paraxial region thereof;

a fifth lens having a positive refractive power and a concave object-side surface in a paraxial region thereof;

a sixth lens having a positive refractive power, and having a convex object-side surface in a paraxial region thereof; and

a seventh lens having a convex object-side surface in a paraxial region, and having a concave image-side surface in a paraxial region thereof,

wherein the optical imaging system comprises a total of seven lenses with refractive power,

wherein the first lens through the seventh lens are sequentially disposed in ascending numerical order from an object side of the optical imaging system toward an imaging plane of the optical imaging system,

wherein a thickness of the fourth lens is greater than a distance from an image-side surface of the third lens to an object-side surface of the fourth lens,

wherein a distance from an image-side surface of the fourth lens to an object-side surface of the fifth lens is greater than a thickness of the second lens, and

wherein an f-number (F No.) of the optical imaging system is less than 1.7.

15. The optical imaging system of claim 14 , wherein the seventh lens has a negative refractive power.

16. The optical imaging system of claim 14 , wherein the optical imaging system satisfies the following conditional expression:

−1.0<( R 9− R 10)/( R 9+ R 10)<1.0

where R9 is a radius of curvature of the object-side surface of the fifth lens, and R10 is a radius of curvature of an image-side surface of the fifth lens.

17. The optical imaging system of claim 14 , wherein the optical imaging system satisfies the following conditional expression:

35< V 1− V 2

where V1 is an Abbe number of the first lens, and V2 is an Abbe number of the second lens.

18. The optical imaging system of claim 14 , wherein the optical imaging system satisfies the following conditional expression:

−31< V 3− V 4

where V3 is an Abbe number of the third lens, and V4 is an Abbe number of the fourth lens.

19. The optical imaging system of claim 14 , wherein the fourth lens has positive refractive power.