Mobile device and optical imaging lens thereof

1. An optical imaging lens, sequentially from an object side to an image side along an optical axis, comprising an aperture stop, and first, second, third, fourth and fifth lens elements, each of said first, second, third, fourth and fifth lens elements having refracting index, an object-side surface facing toward the object side and an image-side surface facing toward the image side and a central thickness defined along the optical axis, wherein:

said object-side surface of said second lens element comprises a concave portion in a vicinity of the optical axis;

said object-side surface of said fourth lens element comprises a convex portion in a vicinity of the optical axis and a convex portion in a vicinity of a periphery of the fourth lens element, and said image-side surface of said fourth lens element comprises a convex portion in a vicinity of the optical axis and a convex portion in a vicinity of a periphery of the fourth lens element;

said image-side surface of said fifth lens element comprises a concave portion in a vicinity of the optical axis;

the optical imaging lens comprises no other lenses having refracting index beyond the five lens elements; and

an air gap between the third lens element and the fourth lens element along the optical axis is represented by G34, a sum of the central thicknesses of all five lens elements is represented by ALT, the central thickness of the third lens element is represented by T3, a back focal length of the optical imaging lens, which is defined as a distance from the image-side surface of the fifth lens element to an image plane along the optical axis, is represented by BFL, and G34, ALT, T3 and BFL satisfy the equations:

4≦ ALT/G 34≦10,

BFL/T 3≦3.53.

2. The optical imaging lens according to claim 1 , wherein the central thickness of the second lens element is represented by T2, and T2 and ALT satisfy the inequality:

16.86≧ ALT/T 2≧5.62.

3. The optical imaging lens according to claim 1 , wherein T3 and ALT satisfy the inequality:

ALT/T 3≦8.27.

4. The optical imaging lens according to claim 1 , wherein the central thickness of the second lens element is represented by T2, a sum of all four air gaps from the first lens element to the fifth lens element along the optical axis is represented by Gaa, and T2 and Gaa satisfy the inequality:

7.40≧ Gaa/T 2≧2.45.

5. The optical imaging lens according to claim 1 , wherein a distance between the object-side surface of the first lens element and an image plane along the optical axis is represented by TTL, and T3 and TTL satisfy the inequality:

TTL/T 3≦15.41.

6. The optical imaging lens according to claim 1 , wherein the central thickness of the fifth lens element is represented by T5, a distance between the object-side surface of the first lens element and an image plane along the optical axis is represented by TTL, and T5 and TTL satisfy the inequality:

25.117≧ TTL/T 5≧10.46.

7. The optical imaging lens according to claim 6 , wherein a sum of all four air gaps from the first lens element to the fifth lens element along the optical axis is represented by Gaa, and G34 and Gaa satisfy the inequality:

4.97≧ Gaa/G 34≧1.66.

8. The optical imaging lens according to claim 1 , wherein an air gap between the fourth lens element and the fifth lens element along the optical axis is represented by G45, and G45 and ALT satisfy the inequality:

ALT/G 45≦30.

9. The optical imaging lens according to claim 1 , wherein the central thickness of the fifth lens element is represented by T5, an air gap between the fourth lens element and the fifth lens element along the optical axis is represented by G45, and T5 and G45 satisfy the inequality:

1.06≦ G 45/ T 5≦3.17.

10. The optical imaging lens according to claim 1 , wherein an air gap between the fourth lens element and the fifth lens element along the optical axis is represented by G45, a distance between the object-side surface of the first lens element and an image plane along the optical axis is represented by TTL, and G45 and TTL satisfy the inequality:

TTL/G 45≦14.85.

11. The optical imaging lens according to claim 1 , wherein an air gap between the fourth lens element and the fifth lens element along the optical axis is represented by G45, a sum of all four air gaps from the first lens element to the fifth lens element along the optical axis is represented by Gaa, and G45 and Gaa satisfy the inequality:

Gaa/G 45≦7.

12. The optical imaging lens according to claim 1 , wherein the central thickness of the second lens element is represented by T2, an air gap between the fourth lens element and the fifth lens element along the optical axis is represented by G45, and T2 and G45 satisfy the inequality:

1.06≦ G 45/ T 2≦3.17.

13. The optical imaging lens according to claim 1 , wherein the central thickness of the fifth lens element is represented by T5, and T5 and ALT satisfy the inequality:

16.86≧ ALT/T 5≧5.62.

14. The optical imaging lens according to claim 1 , wherein an air gap between the first lens element and the second lens element along the optical axis is represented by G12, an air gap between the fourth lens element and the fifth lens element along the optical axis is represented by G45, and G12 and G45 satisfy the inequality:

1.76≦ G 45/ G 12≦5.28.

15. The optical imaging lens according to claim 1 , wherein an air gap between the second lens element and the third lens element along the optical axis is represented by G23, an air gap between the fourth lens element and the fifth lens element along the optical axis is represented by G45, and G23 and G45 satisfy the inequality:

1.49≦ G 45/ G 23≦4.48.

16. The optical imaging lens according to claim 1 , wherein an air gap between the fourth lens element and the fifth lens element along the optical axis is represented by G45, and G34 and G45 satisfy the inequality:

0.71≦ G 45/ G 34≦2.14.

17. The optical imaging lens according to claim 1 , wherein the central thickness of the fourth lens element is represented by T4, an air gap between the fourth lens element and the fifth lens element along the optical axis is represented by G45, and T4 and G45 satisfy the inequality:

T 4/ G 45≦9.

18. The optical imaging lens according to claim 1 , wherein the central thickness of the fifth lens element is represented by T5, an air gap between the fourth lens element and the fifth lens element along the optical axis is represented by G45, and T5 and G45 satisfy the inequality:

T 5/ G 45≦0.71.

19. A mobile device, comprising:

a housing; and

a photography module positioned in the housing and comprising:

an optical imaging lens, sequentially from an object side to an image side along an optical axis, comprising an aperture stop, first, second, third, fourth and fifth lens elements, each of said first, second, third, fourth and fifth lens elements having refracting index, an object-side surface facing toward the object side and an image-side surface facing toward the image side and a central thickness defined along the optical axis, wherein:

said object-side surface of said second lens element comprises a concave portion in a vicinity of the optical axis;

said object-side surface of said fourth lens element comprises a convex portion in a vicinity of the optical axis and a convex portion in a vicinity of a periphery of the fourth lens element, and said image-side surface of said fourth lens element comprises a convex portion in a vicinity of the optical axis and a convex portion in a vicinity of a periphery of the fourth lens element;

said image-side surface of said fifth lens element comprises a concave portion in a vicinity of the optical axis;

the optical imaging lens comprises no other lenses having refracting index beyond the five lens elements; and

an air gap between the third lens element and the fourth lens element along the optical axis is represented by G34, a sum of the central thicknesses of all five lens elements is represented by ALT, the central thickness of the third lens element is represented by T3, a back focal length of the optical imaging lens, which is defined as a distance from the image-side surface of the fifth lens element to an image plane along the optical axis, is represented by BFL, and G34 and ALT, T3 and BFL satisfy the equations:

4≦ ALT/G 34≦10,

BFL/T 3≦3.53;

a lens barrel for positioning the optical imaging lens;

a module housing unit for positioning the lens barrel;

a substrate for positioning the module housing unit; and

an image sensor positioned at the image side of the optical imaging lens.