Optical imaging system

1. An optical imaging system, comprising:

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

a second lens comprising a positive refractive power;

a third lens comprising a negative refractive power and comprising a concave image-side surface;

a fourth lens comprising a positive refractive power; and

a fifth lens comprising a positive refractive power,

wherein the first to fifth lenses are sequentially disposed from an object side toward an imaging plane such that the fifth lens is a lens disposed most adjacent to the imaging plane, and

wherein −2.5<f/f3<−1.5 is satisfied, wherein f is an overall focal length of the optical imaging system, and f3 is a focal length of the third lens.

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

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

4. The optical imaging system of claim 1 , wherein an object-side surface and an image-side surface of the fifth lens are convex.

5. The optical imaging system of claim 1 , further comprising:

a stop disposed between the second lens and the third lens.

6. The optical imaging system of claim 1 , wherein one or more of the first to fifth lenses have a spherical shape.

7. The optical imaging system of claim 1 , wherein one or more of the first to fifth lenses are formed of glass.

8. The optical imaging system of claim 1 , wherein −6.5<{(1/f)*(Y/tan θ)−1}*100<−1.0 is satisfied, in which f is an overall focal length of the optical imaging system, Y is ½ of a diagonal length of the imaging plane, and θ is a half of a field of view of the optical imaging system.

9. The optical imaging system of claim 1 , wherein TL/2Y <2.0 is satisfied, in which TL is a distance from an object-side surface of the first lens to the imaging plane, and 2Y is a diagonal length of the imaging plane.

10. The optical imaging system of claim 1 , wherein −7.0<R1/f<5.0 is satisfied, in which f is an overall focal length of the optical imaging system, and R1 is a radius of curvature of an object-side surface of the first lens.

11. The optical imaging system of claim 1 , wherein −5.5<(R1+R2)/(R1−R2) <5.5 is satisfied, in which R1 is a radius of curvature of an object-side surface of the first lens, and R2 is a radius of curvature of the image-side surface of the first lens.

12. The optical imaging system of claim 1 , wherein 0.2<f/f1<0.6 is satisfied, in which f is an overall focal length of the optical imaging system, and f1 is a focal length of the first lens.

13. The optical imaging system of claim 1 , wherein 5.0<(t1+t2)/t3<12.0 is satisfied, in which t1 is a thickness of an optical axis center of the first lens, t2 is a thickness of an optical axis center of the second lens, and t3 is a thickness of an optical axis center of the third lens.

14. The optical imaging system of claim 1 , wherein 0≤|n1−n2|≤0.20 is satisfied, in which n1 is a refractive index of the first lens, and n2 is a refractive index of the second lens.

15. An optical imaging system, comprising:

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

a second lens comprising positive refractive power;

a third lens comprising a concave image-side surface and a concave object-side surface;

a fourth lens comprising positive refractive power; and

a fifth lens comprising a convex image-side surface and a convex object-side surface,

wherein the first to fifth lenses are sequentially disposed from an object side toward an imaging plane such that the fifth lens is a lens disposed most adjacent to the imaging plane, and

wherein −2.5<f/f3<−1.5 is satisfied, wherein f is an overall focal length of the optical imaging system, and f3 is a focal length of the third lens.

16. An optical imaging system, comprising:

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

a second lens comprising a positive refractive power and comprising a convex object-side surface;

a third lens comprising a negative refractive power and comprising a convex object-side surface and a concave image-side surface;

a fourth lens comprising a positive refractive power; and

a fifth lens comprising a positive refractive power and comprising a concave object-side surface and a convex image-side surface,

wherein the second and third lenses comprise a refractive index greater than a refractive index of the first lens, and the fourth and the fifth lenses comprise a refractive index less than a refractive index of the third lens, and

wherein −2.5<f/f3<−1.5 is satisfied, wherein f is an overall focal length of the optical imaging system, and f3 is a focal length of the third lens.

17. The optical imaging system of claim 16 , wherein an Abbe number of the third lens is lower than an Abbe number of the first lens.

18. The optical imaging system of claim 16 , wherein an Abbe number of the fourth lens and the fifth lens are greater than an Abbe number of the third lens.

19. An optical imaging system, comprising:

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

a second lens comprising a positive refractive power;

a third lens comprising a negative refractive power and comprising a concave image-side surface;

a fourth lens comprising a positive refractive power; and

a fifth lens comprising a positive refractive power,

wherein the first to fifth lenses are sequentially disposed from an object side toward an imaging plane such that the optical imaging system comprises a total of five lenses disposed between the object side and the imaging plane, and

wherein −2.5<f/f3<−1.5 is satisfied, wherein f is an overall focal length of the optical imaging system, and f3 is a focal length of the third lens.