Image capturing lens system, image capturing apparatus and electronic device

1. An image capturing lens system comprising, in order from an object side to an image side:

a first lens element with positive refractive power having an object-side surface being convex in a paraxial region thereof and an image-side surface being concave in a paraxial region thereof;

a second lens element with negative refractive power having an object-side surface being concave in a paraxial region thereof and an image-side surface being convex in a paraxial region thereof;

a third lens element with positive refractive power having an object-side surface being concave in a paraxial region thereof and an image-side surface being convex in a paraxial region thereof; and

a fourth lens element with negative refractive power having an object-side surface being convex in a paraxial region thereof and an image-side surface being concave in a paraxial region thereof, wherein the image-side surface of the fourth lens element comprises at least one convex shape in an off-axis region thereof;

wherein the image capturing lens system has a total of four lens elements, a maximum of axial distances between every two lens elements of the first lens element, the second lens element, the third lens element and the fourth lens element which are adjacent to each other is ATmax, a minimum of the axial distances between every two lens elements of the first lens element, the second lens element, the third lens element and the fourth lens element which are adjacent to each other is ATmin, a curvature radius of the object-side surface of the third lens element is R5, a curvature radius of the image-side surface of the third lens element is R6, an axial distance between the first lens element and the second lens element is T12, an axial distance between the second lens element and the third lens element is T23, an axial distance between the third lens element and the fourth lens element is T34, a central thickness of the second lens element is CT2, and the following conditions are satisfied:

1.0< AT max/ AT min<8.0;

1.0<( R 5+ R 6)/( R 5− R 6)<3.50;

T 34< T 12< T 23; and

0.80< T 23/ CT 2<2.50.

2. The image capturing lens system of claim 1 , wherein the axial distance between the second lens element and the third lens element is T23, a central thickness of the third lens element is CT3, and the following condition is satisfied:

T 23< CT 3.

3. The image capturing lens system of claim 1 , wherein a focal length of the first lens element is f1, a focal length of the fourth lens element is f4, and the following condition is satisfied:

| f 4/ f 1|<0.85.

4. The image capturing lens system of claim 1 , wherein a focal length of the image capturing lens system is f, a vertical distance between a maximum effective diameter on the image-side surface of the fourth lens element and an optical axis is Y42, and the following condition is satisfied:

1.0< f/Y 42<1.40.

5. The image capturing lens system of claim 1 , wherein the maximum of the axial distances between every two lens elements of the first lens element, the second lens element, the third lens element and the fourth lens element which are adjacent to each other is ATmax, the minimum of the axial distances between every two lens elements of the first lens element, the second lens element, the third lens element and the fourth lens element which are adjacent to each other is ATmin, and the following condition is satisfied:

1.25< AT max/ AT min<5.0.

6. The image capturing lens system of claim 1 , wherein a half of a maximal field of view of the image capturing lens system is HFOV, and the following condition is satisfied:

0.78<tan( HFOV )<2.0.

7. The image capturing lens system of claim 1 , wherein a maximum of refractive indexes of the first lens element, the second lens element, the third lens element and the fourth lens element is Nmax, and the following condition is satisfied:

1.65 ≦N max.

8. The image capturing lens system of claim 1 , wherein the axial distance between the first lens element and the second lens element is T12, the axial distance between the third lens element and the fourth lens element is T34, and the following condition is satisfied:

1.0< T 12/ T 34<6.0.

9. The image capturing lens system of claim 1 , wherein a focal length of the first lens element is f1, a focal length of the second lens element is f2, a focal length of the third lens element is f3, a focal length of the fourth lens element is f4, and the following conditions are satisfied:

| f 3|<| f 1|<| f 2|; and

| f 4|<| f 1|<| f 2|.

10. An image capturing lens system comprising, in order from an object side to an image side:

a first lens element with positive refractive power having an object-side surface being convex in a paraxial region thereof and an image-side surface being concave in a paraxial region thereof;

a second lens element with negative refractive power having an object-side surface being concave in a paraxial region thereof and an image-side surface being convex in a paraxial region thereof;

a third lens element with positive refractive power having an object-side surface being concave in a paraxial region thereof and an image-side surface being convex in a paraxial region thereof; and

a fourth lens element with negative refractive power having an object-side surface being convex in a paraxial region thereof and an image-side surface being concave in a paraxial region thereof, wherein the image-side surface of the fourth lens element comprises at least one convex shape in an off-axis region thereof;

wherein the image capturing lens system has a total of four lens elements, a maximum of axial distances between every two lens elements of the first lens element, the second lens element, the third lens element and the fourth lens element which are adjacent to each other is ATmax, a minimum of the axial distances between every two lens elements of the first lens element, the second lens element, the third lens element and the fourth lens element which are adjacent to each other is ATmin, a focal length of the first lens element is f1, a focal length of the second lens element is f2, a focal length of the third lens element is f3, a focal length of the fourth lens element is f4, an f-number of the image capturing lens system is Fno, an Abbe number of the fourth lens element is V4, and the following conditions are satisfied:

1.25< AT max/ AT min<7.0;

(| f 3|+| f 4|)/( f| 1|+| f 2|)<0.65;

1.50< Fno< 2.60; and

V 4<30.

11. The image capturing lens system of claim 10 , wherein the focal length of the first lens element is f1, the focal length of the fourth lens element is f4, and the following condition is satisfied:

| f 4/ f 1|<0.85.

12. The image capturing lens system of claim 10 , wherein a maximum of refractive indexes of the first lens element, the second lens element, the third lens element and the fourth lens element is Nmax, and the following condition is satisfied:

1.65≦ N max.

13. The image capturing lens system of claim 10 , wherein an axial distance between the second lens element and the third lens element is T23, a central thickness of the second lens element is CT2, and the following condition is satisfied:

1.0< T 23/ CT 2<2.0.

14. The image capturing lens system of claim 10 , wherein an axial distance between the first lens element and the second lens element is T12, an axial distance between the second lens element and the third lens element is T23, and the following condition is satisfied:

0.70< T 12/ T 23<2.0.

15. The image capturing lens system of claim 10 , wherein an axial distance between the first lens element and the second lens element is T12, an axial distance between the second lens element and the third lens element is T23, an axial distance between the third lens element and the fourth lens element is T34, and the following condition is satisfied:

T 34< T 12< T 23.

16. The image capturing lens system of claim 10 , wherein a curvature radius of the object-side surface of the third lens element is R5, a curvature radius of the image-side surface of the third lens element is R6, and the following condition is satisfied:

1.0<( R 5+ R 6)/( R 5− R 6)<2.0.

17. The image capturing lens system of claim 10 , wherein a focal length of the image capturing lens system is f, the focal length of the second lens element is f2, and the following condition is satisfied:

f 2/ f<− 3.25.

18. An image capturing apparatus, comprising:

the image capturing lens system of claim 10 , and

an image sensor disposed on an image surface of the image capturing lens system.

19. An electronic device, comprising:

the image capturing apparatus of claim 18 .

20. An image capturing lens system comprising, in order from an object side to an image side:

a first lens element with positive refractive power having an object-side surface being convex in a paraxial region thereof and an image-side surface being concave in a paraxial region thereof;

a second lens element with negative refractive power having an object-side surface being concave in a paraxial region thereof and an image-side surface being convex in a paraxial region thereof;

a third lens element with positive refractive power having an object-side surface being concave in a paraxial region thereof and an image-side surface being convex in a paraxial region thereof; and

a fourth lens element with negative refractive power having an object-side surface being convex in a paraxial region thereof and an image-side surface being concave in a paraxial region thereof, wherein the image-side surface of the fourth lens element comprises at least one convex shape in an off-axis region thereof;

wherein the image capturing lens system has a total of four lens elements, a maximum of axial distances between every two lens elements of the first lens element, the second lens element, the third lens element and the fourth lens element which are adjacent to each other is ATmax, a minimum of the axial distances between every two lens elements of the first lens element, the second lens element, the third lens element and the fourth lens element which are adjacent to each other is ATmin, a ratio of a focal length of the image capturing lens system and a focal length of the first lens element is P1, a ratio of the focal length of the image capturing lens system and a focal length of the second lens element is P2, a ratio of the focal length of the image capturing lens system and a focal length of the third lens element is P3, a ratio of the focal length of the image capturing lens system and a focal length of the fourth lens element is P4, an axial distance between the first lens element and the second lens element is T12, an axial distance between the second lens element and the third lens element is T23, a central thickness of the second lens element is CT2, and the following conditions are satisfied:

1.0< AT max/ AT min<8.0;

1.50<(| P 3|+| P 4|)/(| P 1|+ P 2|)<9.0;

0.70< T 12/ T 23<2.0; and

0.80< T 23/ CT 2<2.50.

21. The image capturing lens system of claim 20 , wherein the axial distance between the first lens element and the second lens element is T12, an axial distance between the third lens element and the fourth lens element is T34, and the following condition is satisfied:

1.80< T 12/ T 34<5.70.

22. The image capturing lens system of claim 20 , wherein a half of a maximal field of view of the image capturing lens system is HFOV, a curvature radius of the object-side surface of the third lens element is R5, a curvature radius of the image-side surface of the third lens element is R6, and the following conditions are satisfied:

0.78<tan( HFOV )<2.0; and

1.0<( R 5+ R 6)/( R 5− R 6)<3.50.

23. The image capturing lens system of claim 20 , wherein the focal length of the first lens element is f1, the focal length of the second lens element is f2, the focal length of the third lens element is f3, the focal length of the fourth lens element is f4, and the following conditions are satisfied:

| f 3|<| f 1|<| f 2|; and

| f 4|<| f 1|<| f 2|.

24. The image capturing lens system of claim 20 , wherein an axial distance between the object-side surface of the first lens element and an image surface is TL, a vertical distance between a maximum effective diameter on the image-side surface of the fourth lens element and an optical axis is Y42, and the following condition is satisfied:

TL/Y 42<2.0.

25. The image capturing lens system of claim 20 , wherein the focal length of the image capturing lens system is f, a vertical distance between a maximum effective diameter on the image-side surface of the fourth lens element and an optical axis is Y42, and the following condition is satisfied:

1.0< f/Y 42<1.40.