Optical imaging system comprising four lenses of ++++ refractive powers

1. An optical imaging system, comprising:

a first lens having positive refractive power, a second lens having positive refractive power, a third lens having positive refractive power and comprising a convex object-side surface, and a fourth lens having positive refractive power, sequentially disposed from an object side to an image surface of the optical imaging system,

wherein an F No. of the optical imaging system is equal to or less than 1.0, and

wherein a distance along an optical axis from an image-side surface of the second lens to the object-side surface of the third lens is greater than a distance along the optical axis from an image-side surface of the first lens to an object-side surface of the second lens.

2. The optical imaging system of claim 1 , wherein visible light transmission of the first lens is equal to or less than 5%.

3. The optical imaging system of claim 1 , wherein the second lens comprises an inflection point on an image-side surface.

4. The optical imaging system of claim 1 , wherein the third lens comprises a convex image-side surface.

5. The optical imaging system of claim 1 , wherein the fourth lens comprises a concave image-side surface.

6. The optical imaging system of claim 1 , wherein

5.0<(f1+f2)/f<80,

where f is a focal length of the optical imaging system, f1 is a focal length of the first lens, and f2 is a focal length of the second lens.

7. The optical imaging system of claim 1 , wherein

1.0<f3/f <2.5,

where f is a focal length of the optical imaging system, and f3 is a focal length of the third lens.

8. The optical imaging system of claim 1 , wherein

1.0<f4/f <6.0,

where f is a focal length of the optical imaging system, and f4 is a focal length of the fourth lens.

9. The optical imaging system of claim 1 , wherein

0.3<R1/f<2.0,

where f is a focal length of the optical imaging system, and R1 is a radius of curvature of an object-side surface of the first lens.

10. The optical imaging system of claim 1 , wherein

0.3<R3/f<2.0,

where f is a focal length of the optical imaging system, and R3 is a radius of curvature of an object-side surface of the second lens.

11. The optical imaging system of claim 1 , wherein

5.0<R5/f<80,

where f is a focal length of the optical imaging system, and R5 is a radius of curvature of an object-side surface of the third lens.

12. The optical imaging system of claim 1 , wherein

1.580<Nd1<1.640,

where Nd1 is a refractive index of the first lens.

13. The optical imaging system of claim 1 , wherein

1.0<TTL/f <2.0,

where TTL is a distance from an object-side surface of the lens closest to the object side to the image surface, and f is a focal length of the optical imaging system.

14. The optical imaging system of claim 1 , wherein

0.3<R1/TTL <5.0,

where TTL is a distance from an object-side surface of the lens closest to the object side to the image surface, and R1 is a focal length of the lens closest to the object side.

15. The optical imaging system of claim 1 , wherein

0.5<EPD/TTL <0.7,

where TTL is a distance from an object-side surface of the lens closest to the object side to the image surface, and EPD is a diameter of an entrance pupil.

16. An optical imaging system, comprising:

a first lens having positive refractive power, a second lens having positive refractive power and comprising an inflection point on an image-side surface, a third lens having positive refractive power, and a fourth lens having positive refractive power, sequentially disposed from an object side to an image surface of the optical imaging system,

wherein an F No. of the optical imaging system is equal to or less than 1.0.