Photographing optical lens system, image capturing unit and electronic device

1. A photographing optical lens system comprising, in order from an object side to an image side:

a first lens element;

a second lens element having positive refractive power;

a third lens element;

a fourth lens element;

a fifth lens element;

a sixth lens element;

a seventh lens element; and

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

wherein the photographing optical lens system has a total of eight lens elements, a focal length of the photographing optical lens system is f, a focal length of the first lens element is f1, a focal length of the second lens element is f2, a vertical distance between a non-axial critical point on the image-side surface of the eighth lens element and an optical axis is Yc82, and the following conditions are satisfied:

−0.25< f 2/ f 1<1.25; and

0.10< Yc 82/ f< 0.80.

2. The photographing optical lens system of claim 1 , wherein the first lens element has an object-side surface being convex in a paraxial region thereof.

3. The photographing optical lens system of claim 1 , wherein an axial distance between an object-side surface of the first lens element and the image-side surface of the eighth lens element is Td, the focal length of the photographing optical lens system is f, and the following condition is satisfied:

Td/f< 1.50.

4. The photographing optical lens system of claim 1 , wherein an axial distance between an object-side surface of the first lens element and an image surface is TL, a maximum image height of the photographing optical lens system is ImgH, and the following condition is satisfied:

TL /ImgH<2.0.

5. The photographing optical lens system of claim 1 , wherein the focal length of the photographing optical lens system is f, a composite focal length of the first lens element, the second lens element and the third lens element is f123, and the following condition is satisfied:

0.30< f/f 123<1.5.

6. The photographing optical lens system of claim 1 , wherein a sum of central thicknesses of the lens elements of the photographing optical lens system is ΣCT, an axial distance between the image-side surface of the eighth lens element and an image surface is BL, and the following condition is satisfied:

2.5<Σ CT/BL< 6.0.

7. The photographing optical lens system of claim 1 , wherein a curvature radius of the object-side surface of the eighth lens element is R15, a curvature radius of the image-side surface of the eighth lens element is R16, and the following condition is satisfied:

−0.5<( R 15+ R 16)/( R 15− R 16).

8. The photographing optical lens system of claim 1 , wherein the seventh lens element has an image-side surface being convex in a paraxial region thereof, and the seventh lens element has positive refractive power.

9. The photographing optical lens system of claim 8 , wherein the focal length of the second lens element is f2, a focal length of the seventh lens element is f7, and the following condition is satisfied:

| f 7/ f 2|<1.0.

10. The photographing optical lens system of claim 1 , wherein a maximum image height of the photographing optical lens system is ImgH, the focal length of the photographing optical lens system is f, and the following condition is satisfied:

0.65<ImgH/ f< 1.40.

11. The photographing optical lens system of claim 1 , wherein a maximum effective radius of an object-side surface of the first lens element is Y11, a maximum effective radius of the image-side surface of the eighth lens element is Y82, and the following condition is satisfied:

Y 11/ Y 82<1.0.

12. The photographing optical lens system of claim 1 , wherein the focal length of the photographing optical lens system is f, a composite focal length of the fourth lens element, the fifth lens element and the sixth lens element is f456, and the following condition is satisfied:

| f/f 456|<0.60.

13. The photographing optical lens system of claim 1 , wherein a sum of central thicknesses of the lens elements of the photographing optical lens system is ΣCT, an axial distance between the image-side surface of the eighth lens element and an image surface is BL, and the following condition is satisfied:

2.0<Σ CT/BL< 10.

14. The photographing optical lens system of claim 1 , wherein the seventh lens element has an image-side surface being concave in a paraxial region thereof, at least one of an object-side surface and an image-side surface of the seventh lens element has at least one inflection point, and both the object-side surface and the image-side surface of the seventh lens element are aspheric.

15. The photographing optical lens system of claim 14 , wherein the focal length of the second lens element is f2, a focal length of the seventh lens element is f7, and the following condition is satisfied:

1.0<| f 7/ f 2|.

16. The photographing optical lens system of claim 1 , wherein an axial distance between an object-side surface of the first lens element and the image-side surface of the eighth lens element is Td, an entrance pupil diameter of the photographing optical lens system is EPD, and the following condition is satisfied:

Td/EPD< 3.0.

17. The photographing optical lens system of claim 1 , further comprising a aperture stop, wherein an axial distance between the aperture stop and the image-side surface of the eighth lens element is Sd, an axial distance between an object-side surface of the first lens element and the image-side surface of the eighth lens element is Td, and the following condition is satisfied:

0.70< Sd/Td< 1.20.

18. An image capturing unit, comprising:

the photographing optical lens system of claim 1 ; and

an image sensor, wherein the image sensor is disposed on the image side of the photographing optical lens system.

19. An electronic device, comprising:

the image capturing unit of claim 18 .