Optical imaging system

1. An optical imaging system comprising:

a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, and a seventh lens, wherein the first to seventh lenses are sequentially disposed along an optical axis from an object side of the optical imaging system toward an imaging plane of the optical imaging system,

wherein the first lens has a concave image-side surface,

the second lens has a negative refractive power,

the fourth lens has a convex object-side surface;

the fifth lens has a concave image-side surface,

four or more lenses among the first to seventh lenses have a refractive index greater than 1.6, and

the first to seventh lenses are the only lenses disposed between the object side of the optical imaging system and the imaging plane of the optical imaging system.

2. The optical imaging system of claim 1 , wherein the first to seventh lenses are made of a plastic material.

3. The optical imaging system of claim 1 , wherein the concave image-side surface of the first lens is concave along the optical axis, and

the first lens further has a convex object-side surface along the optical axis.

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

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

6. The optical imaging system of claim 1 , wherein the convex object-side surface of the fourth lens is convex along an optical axis, and

the fourth lens further has a convex image-side surface along the optical axis.

7. The optical imaging system of claim 1 , wherein the concave image-side surface of the fifth lens is concave along the optical axis, and

the fifth lens further has a convex object-side surface along the optical axis.

8. The optical imaging system of claim 1 , wherein the sixth lens has a convex object-side surface along the optical axis and a concave image-side surface along the optical axis.

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

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

V 2+ V 3< V 1

where V1 represents an Abbe number of the first lens, V2 represents an Abbe number of the second lens, and V3 represents an Abbe number of the third lens.

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

V 5+ V 6< V 4

where V4 represents an Abbe number of the fourth lens, V5 represents an Abbe number of the fifth lens, and V6 represents an Abbe number of the sixth lens.

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

CT 2<0.2 mm

where CT2 represents a thickness of the second lens.

13. The optical imaging system of claim 1 , wherein an f-number of the optical imaging system is less than or equal to 2.09.

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

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

16. An optical imaging system comprising:

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

a second lens having a refractive index greater than or equal to 1.65;

a third lens having a positive refractive power and a refractive index greater than or equal to 1.65;

a fourth lens having a positive refractive power;

a fifth lens having a refractive index greater than or equal to 1.65;

a sixth lens having a refractive index greater than or equal to 1.65; and

a seventh lens having a positive refractive power,

wherein the first to seventh lenses are sequentially disposed from an object side toward an imaging plane.

17. The optical imaging system of claim 16 , wherein the sixth lens has an inflection point on one or both of an object-side surface or an image-side surface.

18. The optical imaging system of claim 16 , wherein the seventh lens has an inflection point on one or both of an object-side surface or an image-side surface.

19. An optical imaging system comprising:

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

a second lens having a negative refractive power;

a third lens having a positive refractive power;

a fourth lens having a positive refractive power;

a fifth lens having a positive refractive power;

a sixth lens having a negative refractive power; and

a seventh lens having a positive refractive power,

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

the second lens, the third lens, the fifth lens, and the sixth lens each have a refractive index greater than or equal to 1.65, and

an f-number of the optical imaging system is less than or equal to 2.09.

20. The optical imaging system of claim 19 , wherein the first lens, the second lens, the fourth lens, and the seventh lens each have a convex object-side surface along an optical axis.

21. The optical imaging system of claim 19 , wherein the optical imaging system satisfies the following expression:

1.0< TTL/f

where TTL represents a distance from an object-side surface of the first lens to the imaging plane, and f represents a focal length of the optical imaging system.