Optical imaging system

1. An optical imaging system comprising:

a first lens comprising a positive refractive power, wherein an object-side surface of the first lens is convex;

a second lens comprising a negative refractive power, wherein an image-side surface of the second lens is concave;

a third lens comprising refractive power, wherein an object-side surface of the third lens is convex and an image-side surface of the third lens is concave;

a fourth lens comprising refractive power, wherein an object-side surface of the fourth lens is concave; and

a fifth lens comprising refractive power, wherein an object-side surface of the fifth lens is concave and an image-side surface of the fifth lens is convex in a paraxial portion,

wherein the first to fifth lenses are sequentially disposed from an object side of the optical imaging system, towards an imaging plane

where 0.70<TTL/f<1.1, in which TTL is a distance of the object-side surface of the first lens to the imaging plane, and f is an overall focal length of the optical imaging system, and

a focal length f1 of the first lens is in a range of 2.50 to 3.00.

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

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

4. The optical imaging system of claim 1 , where 1.10<TTL/ImgH, in which TTL is a distance of the object-side surface of the first lens to the imaging plane, and ImgH is ½ of a diagonal length of the imaging plane.

5. The optical imaging system of claim 1 , where 20<FOV<35, in which FOV is a half of a field of view of the optical imaging system.

6. The optical imaging system of claim 1 , where 0.16<R 1 /f<2.0, in which R 1 is a radius of curvature of the object-side surface of the first lens, and f is an overall focal length of the optical imaging system.

7. The optical imaging system of claim 1 , wherein one of the first through fifth lenses has a meniscus shape.

8. The optical imaging system of claim 1 , wherein one of the first through fifth lenses has an aspherical shape.

9. An optical imaging system comprising:

a first lens, comprising a convex object-side surface;

a second lens, comprising a concave image-side surface;

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

a fourth lens, comprising a concave object-side surface and a convex image-side surface; and

a fifth lens, comprising a concave object-side surface and a convex image-side surface where the fifth lens crosses an optical axis,

wherein the first to fifth lenses are sequentially disposed from an object side of the optical imaging system, toward an imaging plane,

where 0.70<TTL/f<1.1, in which TTL is a distance of the object-side surface of the first lens to the imaging plane, and f is an overall focal length of the optical imaging system, and

a focal length f1 of the first lens is in a range of 2.50 to 3.00.

10. The optical imaging system of claim 9 , wherein the first lens and the fourth lens have the same sign of refractive power.

11. The optical imaging system of claim 9 , wherein the second lens and the third lens have the same sign of refractive power.

12. The optical imaging system of claim 9 , further comprising:

a stop located adjacent to the object-side surface of the first lens.

13. The optical imaging system of claim 9 , wherein one of the first through fifth lenses has a meniscus shape.

14. The optical imaging system of claim 9 , wherein one of the first through fifth lenses has an aspherical shape.

15. The optical imaging system of claim 1 , wherein an image-side surface of the fifth lens is entirely convex.