Optical imaging system

1. An optical imaging system comprising:

a first lens having a convex or concave object-side surface at an optical axis and an image-side surface that is concave;

a second lens having a refractive power and an image-side surface that is concave;

a third lens having an object-side surface that is convex;

a fourth lens having an image-side surface that is concave;

a fifth lens having a refractive power; and

a sixth lens having a refractive power and an image-side surface having an inflection point;

wherein the first lens through the sixth lens are sequentially disposed in numerical order from an object side of the optical imaging system toward an imaging plane of the optical imaging system, and

the optical imaging system satisfies the following conditional expressions:

TL/(2Y)≤1.01 1.2≤tan θ

where TL is a distance from an object-side surface of the first lens to the imaging plane, 2Y is a diagonal length of the imaging plane, and 6 is half of a field of view of the optical imaging system.

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

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

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

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

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

7. The optical imaging system of claim 1 , wherein the image-side surface of the sixth lens is concave.

8. The optical imaging system of claim 1 , wherein the optical imaging system further satisfies the following conditional expression:

−35<{(1/f)*(Y/tan θ)−1}*100<−5.0

where f is an overall focal length of the optical imaging system, and Y is half of the diagonal length of the imaging plane.

9. The optical imaging system of claim 1 , wherein the optical imaging system further satisfies the following conditional expression:

0.3<(R1+R2)/(R1−R2)<3.0

where 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.

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

0.1<═f/f3═<2.0

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

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

1.8<f/EPD <2.4

where f is an overall focal length of the optical imaging system, and EPD is an entrance pupil diameter of the optical imaging system.

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

0.4<(t1+t2)/t3<2.0

where t1 is a thickness of the first lens measured along the optical axis of the first lens, t2 is a thickness of the second lens measured along an optical axis of the second lens, and t3 is a thickness of the third lens measured along an optical axis of the third lens.

13. The optical imaging system of claim 1 , wherein the optical imaging system further satisfies the following conditional expression:

30<V5−V6<40

where V5 is an Abbe number of the fifth lens, and V6 is an Abbe number of the sixth lens.

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

15. An optical imaging system comprising:

a first lens having a refractive power and comprising a convex or concave object-side surface at an optical axis;

a second lens having a refractive power and an image-side surface that is concave;

a third lens having a refractive power;

a fourth lens having an image-side surface that is concave;

a fifth lens having an image-side surface that is convex; and

a sixth lens having a refractive power and an image-side surface having an inflection point,

wherein the first lens through the sixth lens are sequentially disposed in numerical order from an object side of the optical imaging system toward an imaging plane of the optical imaging system, and

the optical imaging system satisfies the following conditional expressions:

TL/(2Y)≤1.01

0.3<(R1+R2)/(R1−R2)<3.0

where TL is a distance from an object-side surface of the first lens to the imaging plane, 2Y is a diagonal length of the imaging plane, R1 is a radius of curvature of an object-side surface of the first lens, and R2 is a radius of curvature of an image-side surface of the first lens.

16. The optical imaging system of claim 15 , wherein the image-side surface of the first lens is concave.

17. The optical imaging system of claim 15 , wherein an object-side surface of the second lens is convex.

18. An optical imaging system comprising:

a first lens having a refractive power and comprising a convex or concave object-side surface at an optical axis;

a second lens having a refractive power and an image-side surface that is concave;

a third lens having a refractive power;

a fourth lens having a refractive power;

a fifth lens having a refractive power; and

a sixth lens having a refractive power and a surface having an inflection point;

wherein the first lens through the sixth lens are sequentially disposed in numerical order from an object side of the optical imaging system toward an imaging plane of the optical imaging system,

the refractive power of the first lens and the refractive power of the sixth lens have a same sign,

the refractive power of the second lens and the refractive power of the fifth lens have a same sign,

the refractive power of the third lens and the refractive power of the fourth lens have different signs, and

the optical imaging system satisfies any one or any combination of any two or more of the following conditional expressions:

TL/(2Y)≤1.01

1.2≤tan θ

0.3<(R1+R2)/(R1−R2)<3.0

where TL is a distance from an object-side surface of the first lens to the imaging plane, 2Y is a diagonal length of the imaging plane, 6 is half of a field of view of the optical imaging system, R1 is a radius of curvature of an object-side surface of the first lens, and R2 is a radius of curvature of an image-side surface of the first lens.

19. The optical imaging system of claim 18 , wherein the first lens and the sixth lens each have a negative refractive power,

the second lens and the fifth lens each have a positive refractive power, and

the third lens has a positive refractive power and the fourth lens has a negative refractive power, or the third lens has a negative refractive power and the fourth lens has a positive refractive power.

20. The optical imaging system of claim 18 , wherein the image-side surface of the first lens is concave,

an object-side surface of the third lens is convex,

an image-side surface of the fourth lens is concave, and

an image-side surface of the fifth lens is convex.

21. The optical imaging system of claim 18 , wherein the first lens, the third lens, and the fifth lens each have a refractive index less than 1.6 and the second lens, the fourth lens, and the sixth lens each have a refractive index greater than 1.62 and less than 2.0, or the second lens and the fifth lens each have a refractive index less than 1.6 and the first lens, the third lens, the fourth lens, and the sixth lens each have a refractive index greater than 1.65 and less than 2.0.