Image capturing optical system, image capturing device and portable device

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

a first lens element with positive refractive power having a convex object-side surface in a paraxial region thereof;

a second lens element with negative refractive power;

a third lens element;

a fourth lens element having a concave image-side surface in a paraxial region thereof;

a fifth lens element having a concave image-side surface in a paraxial region thereof; wherein both of an object-side surface and the image-side surface of the fifth lens element are aspheric, the fifth lens element is made of plastic, and the image-side surface thereof has at least one convex shape in an off-axis region thereof; and

a sixth lens element having a concave image-side surface in a paraxial region thereof; wherein both of an object-side surface and the image-side surface of the sixth lens element are aspheric, the sixth lens element is made of plastic, and the image-side surface thereof has at least one convex shape in an off-axis region thereof;

wherein the image capturing optical system has a total of six lens elements;

wherein an axial distance between the third lens element and the fourth lens element is T34, a central thickness of the fifth lens element is CT5, a curvature radius of the object-side surface of the sixth lens element is R11, a curvature radius of the image-side surface of the sixth lens element is R12, a sum of the central thicknesses of the first lens element, the second lens element, the third lens element, the fourth lens element, the fifth lens element, and the sixth lens element is ΣCT, an axial distance between the object-side surface of the first lens element and the image-side surface of the sixth lens element is Td, and the following conditions are satisfied:

0.70< T 34/CT5;

−0.30<( R 11+ R 12)/( R 11− R 12); and

0.55<ΣCT/ Td< 0.95.

2. The image capturing optical system of claim 1 , wherein the axial distance between the third lens element and the fourth lens element is T34, the central thickness of the fifth lens element is CT5, and the following condition is satisfied:

1.0< T 34/CT5<3.0.

3. The image capturing optical system of claim 2 , wherein the axial distance between the third lens element and the fourth lens element is T34, the central thickness of the fifth lens element is CT5, and the following condition is satisfied:

1.25< T 34/CT5<2.50.

4. The image capturing optical system of claim 2 , wherein the second lens element has a concave image-side surface in a paraxial region thereof.

5. The image capturing optical system of claim 1 , wherein the curvature radius of the image-side surface of the sixth lens element is R12, a curvature radius of the image-side surface of the fifth lens element is R10, a curvature radius of the image-side surface of the fourth lens element is R8, and the following condition is satisfied:

0< R 12< R 10< R 8.

6. The image capturing optical system of claim 5 , wherein an Abbe number of the fifth lens element is V5, and the following condition is satisfied:

V 5<32.

7. The image capturing optical system of claim 5 , wherein a focal length of the image capturing optical system is f, an axial distance between the fifth lens element and the six lens element is T56, and the following condition is satisfied:

12.5< f/T 56<25.0.

8. The image capturing optical system of claim 5 , wherein the curvature radius of the object-side surface of the sixth lens element is R11, the curvature radius of the image-side surface of the sixth lens element is R12, and the following condition is satisfied:

2.0<( R 11+ R 12)/( R 11− R 12).

9. The image capturing optical system of claim 1 , wherein the image capturing optical system further comprises a stop, an axial distance from the stop to the image-side surface of the sixth lens element is Sd, an axial distance between the object-side surface of the first lens element and the image-side surface of the sixth lens element is Td, and the following condition is satisfied:

0.80< Sd/Td< 1.10.

10. The image capturing optical system of claim 9 , wherein the central thickness of the fifth lens element is CT5, a central thickness of the sixth lens element is CT6, and the following condition is satisfied:

0.25<CT5/CT6<0.75.

11. The image capturing optical system of claim 9 , wherein an f-number of the image capturing optical system is Fno, and the following condition is satisfied:

1.6 <Fno< 2.5.

12. The image capturing optical system of claim 1 , wherein the fifth lens element has a convex object-side surface in a paraxial region thereof, and the sixth lens element has a convex object-side surface in a paraxial region thereof.

13. The image capturing optical system of claim 1 , wherein the axial distance between the object-side surface of the first lens element and the image-side surface of the sixth lens element is Td, a half of the maximal field of view of the image capturing optical system is HFOV, and the following condition is satisfied:

4.0 mm< Td /Tan(HFOV)<7.5 mm.

14. The image capturing optical system of claim 1 , wherein a focal length of the second lens element is f2, a focal length of any of the third lens element, the fourth lens element, the fifth lens element, and the sixth lens element is fx (i.e. x=3, 4, 5, or 6), and the following condition is satisfied:

| f 2 |<|fx|.

15. The image capturing optical system of claim 1 , wherein a vertical distance between an optical axis and a critical point being the closest to an image surface and on the off-axis region of the image-side surface of the sixth lens element is Yc62, a vertical distance between an optical axis and a critical point being the closest to the image surface and on the off-axis region of the image-side surface of the fifth lens element is Yc52, and the following condition is satisfied:

Yc 62> Yc 52.

16. An image capturing device, comprising:

the image capturing optical system of claim 1 ; and

an image sensor.

17. A portable device, comprising:

the image capturing device of claim 16 .

18. An image capturing optical system comprising, in order from an object side to an image side:

a first lens element with positive refractive power having a convex object-side surface in a paraxial region thereof;

a second lens element with negative refractive power having a concave image-side surface in a paraxial region thereof;

a third lens element;

a fourth lens element having a concave image-side surface in a paraxial region thereof;

a fifth lens element having a convex object-side surface in a paraxial region thereof and a concave image-side surface in a paraxial region thereof;

wherein both of the object-side surface and the image-side surface of the fifth lens element are aspheric, the fifth lens element is made of plastic, and the image-side surface thereof has at least one convex shape in an off-axis region thereof; and

a sixth lens element having a concave image-side surface in a paraxial region thereof; wherein both of an object-side surface and the image-side surface of the sixth lens element are aspheric, the sixth lens element is made of plastic, and the image-side surface thereof has at least one convex shape in an off-axis region thereof;

wherein the image capturing optical system has a total of six lens elements,

wherein an axial distance between the third lens element and the fourth lens element is T34, a central thickness of the fifth lens element is CT5, a curvature radius of the object-side surface of the sixth lens element is R11, a curvature radius of the image-side surface of the sixth lens element is R12, a sum of the central thicknesses of the first lens element, the second lens element, the third lens element, the fourth lens element, the fifth lens element, and the sixth lens element is ΣCT, an axial distance between the object-side surface of the first lens element and the image-side surface of the sixth lens element is Td, and the following conditions are satisfied:

0.50< T 34/CT5;

−0.30<( R 11+ R 12)/( R 11− R 12); and

0.55<ΣCT/ Td< 0.95.

19. The image capturing optical system of claim 18 , wherein a focal length of the second lens element is f2, a focal length of any of the third lens element, the fourth lens element, the fifth lens element, and the sixth lens element is fx (i.e. x=3, 4, 5, or 6), and the following condition is satisfied:

| f 2 |<|fx|.

20. The image capturing optical system of claim 18 , wherein the axial distance between the object-side surface of the first lens element and the image-side surface of the sixth lens element is Td, a half of the maximal field of view of the image capturing optical system is HFOV, and the following condition is satisfied:

4.0 mm< Td /Tan(HFOV)<7.5 mm.

21. The image capturing optical system of claim 18 , wherein the axial distance between the third lens element and the fourth lens element is T34, the central thickness of the fifth lens element is CT5, and the following condition is satisfied:

1.0< T 34/CT5<3.0.

22. The image capturing optical system of claim 18 , wherein the curvature radius of the image-side surface of the sixth lens element is R12, a curvature radius of the image-side surface of the fifth lens element is R10, a curvature radius of the image-side surface of the fourth lens element is R8, and the following condition is satisfied:

0< R 12< R 10< R 8.

23. The image capturing optical system of claim 18 , wherein an f-number of the image capturing optical system is Fno, and the following condition is satisfied:

1.6< Fno< 2.5.

24. The image capturing optical system of claim 18 , wherein the central thickness of the fifth lens element is CT5, a central thickness of the sixth lens element is CT6, and the following condition is satisfied:

0.25<CT5/CT6<0.75.

25. The image capturing optical system of claim 18 , wherein a vertical distance between an optical axis and a critical point being the closest to an image surface and on the off-axis region of the image-side surface of the sixth lens element is Yc62, a vertical distance between an optical axis and a critical point being the closest to the image surface and on the off-axis region of the image-side surface of the fifth lens element is Yc52, and the following condition is satisfied:

Yc 62> Yc 52.

26. An image capturing device, comprising:

the image capturing optical system of claim 18 ; and

an image sensor.

27. A portable device, comprising:

the image capturing device of claim 26 .