Optical imaging system

1. An optical imaging system comprising:

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

a third lens having a positive refractive power;

a fourth lens having a negative refractive power;

a fifth lens having a positive refractive power;

a sixth lens having a refractive power; and

a seventh lens having a refractive power,

wherein the first to seventh lenses are sequentially arranged in ascending numerical order along an optical axis of the optical imaging system from an object side of the optical imaging system toward an image side of the optical imaging system,

TTL/f<1.3, where TTL is a distance along the optical axis from the object-side surface of the first lens to an imaging plane of the optical imaging system, and f is an overall focal length of the optical imaging system, and

−0.38≤R10/f≤−0.32, where R10 is a radius of curvature of an image-side surface of the fifth lens at the optical axis, and f is the overall focal length of the optical imaging system.

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

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

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

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

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

7. The optical imaging system of claim 1 , wherein the fifth lens has a concave object-side surface in a paraxial region thereof.

8. The optical imaging system of claim 7 , wherein the image-side surface of the fifth lens is convex in a paraxial region thereof.

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

10. The optical imaging system of claim 1 , wherein the fourth lens is made of a plastic material having an Abbe number, and the fifth lens is made of a plastic material having an Abbe number that is different from the Abbe number of the plastic material of the fourth lens.

11. The optical imaging system of claim 1 , wherein the fifth to seventh lenses have a same Abbe number.

12. The optical imaging system of claim 1 , wherein the fifth to seventh lenses have a same refractive index.

13. The optical imaging system of claim 1 , wherein the first lens is made of a plastic material having an Abbe number, and the second lens is made of a plastic material having an Abbe number that is different from the Abbe number of the plastic material of the first lens.

14. The optical imaging system of claim 13 , wherein the second lens is made of a plastic material having an Abbe number, and the third lens is made of a plastic material having an Abbe number that is different from the Abbe number of the plastic material of the second lens.

15. The optical imaging system of claim 14 , wherein the third lens is made of a plastic material having an Abbe number, and the fourth lens is made of a plastic material having an Abbe number that is different from the Abbe number of the plastic material of the third lens.

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