Image picking-up system, image capturing apparatus and electronic device

1. An image picking-up system comprising seven lens elements, the seven lens elements being, in order from an object side to an image side:

a first lens element, a second lens element, a third lens element, a fourth lens element, a fifth lens element, a sixth lens element and a seventh lens element;

wherein each of the seven lens elements has an object-side surface facing towards the object side and an image-side surface facing towards the image side;

wherein the first lens element has negative refractive power, and the object-side surface of the first lens element is concave in a paraxial region thereof; the second lens element has positive refractive power; the object-side surface of the seventh lens element is convex in a paraxial region thereof, and the image-side surface of the seventh lens element is concave in a paraxial region thereof and comprises at least one convex shape in an off-axis region thereof;

wherein the image picking-up system further comprises an aperture stop, a focal length of the image picking-up system is f, a focal length of the fifth lens element is f5, a maximum among refractive indices of all lens elements of the image picking-up system is Nmax, an axial distance between the aperture stop and the image-side surface of the seventh lens element is SD, an axial distance between the object-side surface of the first lens element and the image-side surface of the seventh lens element is TD, and the following conditions are satisfied:

−1.0< f/f 5<0.40;

1.60< N max<1.72; and

0.50 <SD/TD< 1.20.

2. The image picking-up system of claim 1 , wherein the image-side surface of the third lens element is convex in a paraxial region thereof.

3. The image picking-up system of claim 1 , wherein the maximum among the refractive indices of all lens elements of the image picking-up system is Nmax, and the following condition is satisfied:

1.671 ≤N max<1.72.

4. The image picking-up system of claim 1 , wherein a number of the lens elements of the image picking-up system having an Abbe number smaller than 30 is Nv30, and the following condition is satisfied:

3 ≤Nv 30.

5. The image picking-up system of claim 1 , wherein an f-number of the image picking-up system is Fno, and the following condition is satisfied:

1.20< Fno≤ 2.20.

6. The image picking-up system of claim 1 , wherein a curvature radius of the image-side surface of the second lens element is R4, a curvature radius of the object-side surface of the third lens element is R5, and the following condition is satisfied:

0< R 4/ R 5≤0.93.

7. The image picking-up system of claim 1 , wherein a sum of axial distances between each of adjacent lens elements of the image picking-up system is ΣAT, a sum of central thicknesses of all lens elements of the image picking-up system is ΣCT, a maximum among the central thicknesses of all lens elements of the image picking-up system is CTmax, a vertical distance between a critical point in the off-axis region on the image-side surface of the seventh lens element and an optical axis is Yc72, and the following conditions are satisfied:

Σ AT/ΣCT< 0.75; and

0.20< CT max/ Yc 72<4.0.

8. The image picking-up system of claim 1 , 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, a minimum among central thicknesses of all the lens elements of the image picking-up system is CTmin, and the following condition is satisfied:

1.22≤( T 12+ T 23+ T 34)/ CT min<3.80.

9. An image capturing apparatus, comprising:

the image picking-up system of claim 1 ; and

an image sensor disposed on an image surface of the image picking-up system.

10. An electronic device, comprising:

the image capturing apparatus of claim 9 .

11. An image picking-up system comprising seven lens elements, the seven lens elements being, in order from an object side to an image side:

a first lens element, a second lens element, a third lens element, a fourth lens element, a fifth lens element, a sixth lens element and a seventh lens element;

wherein each of the seven lens elements has an object-side surface facing towards the object side and an image-side surface facing towards the image side;

wherein the first lens element has negative refractive power, and the object-side surface of the first lens element is concave in a paraxial region thereof; the image-side surface of the seventh lens element is concave in a paraxial region thereof and comprises at least one convex shape in an off-axis region thereof;

wherein the image picking-up system further comprises an aperture stop, an axial distance between the second lens element and the third lens element is greater than an axial distance between the third lens element and the fourth lens element, a focal length of the image picking-up system is f, a focal length of the fifth lens element is f5, a maximum among refractive indices of all lens elements of the image picking-up system is Nmax, an axial distance between the aperture stop and the image-side surface of the seventh lens element is SD, an axial distance between the object-side surface of the first lens element and the image-side surface of the seventh lens element is TD, and the following conditions are satisfied:

−1.0< f/f 5<0.40;

1.60< N max<1.72; and

0.50< SD/TD< 1.20.

12. The image picking-up system of claim 11 , wherein the image-side surface of the sixth lens element is convex in a paraxial region thereof.

13. The image picking-up system of claim 11 , wherein the third lens element has positive refractive power; at least one of the object-side and the image-side surfaces of the first lens element comprises at least one inflection point.

14. The image picking-up system of claim 11 , wherein an f-number of the image picking-up system is Fno, a vertical distance between a maximum effective radius position of the object-side surface of the first lens element and an optical axis is Y11, a vertical distance between a maximum effective radius position of the image-side surface of the seventh lens element and the optical axis is Y72, and the following conditions are satisfied:

1.35< Fno< 2.40; and

0.25 <Y 11 /Y 72<1.30.

15. The image picking-up system of claim 11 , wherein a focal length of the fourth lens element is f4, the focal length of the fifth lens element is f5, and the following condition is satisfied:

| f 4 /f 5|<1.0.

16. The image picking-up system of claim 11 , wherein an axial distance between the object-side surface of the first lens element and an image surface is TL, a maximum image height of the image picking-up system is ImgH, and the following condition is satisfied:

1.0< TL/ImgH≤ 2.0.

17. The image picking-up system of claim 11 , wherein a maximum among axial distances between each of adjacent lens elements of the image picking-up system is ATmax, a minimum among central thicknesses of all lens elements of the image picking-up system is CTmin, and the following condition is satisfied:

0.40< AT max/ CT min≤2.56.

18. An image picking-up system comprising seven lens elements, the seven lens elements being, in order from an object side to an image side:

a first lens element, a second lens element, a third lens element, a fourth lens element, a fifth lens element, a sixth lens element and a seventh lens element;

wherein each of the seven lens elements has an object-side surface facing towards the object side and an image-side surface facing towards the image side;

wherein the first lens element has negative refractive power, and the object-side surface of the first lens element is concave in a paraxial region thereof; the object-side surface of the seventh lens element is convex in a paraxial region thereof, and the image-side surface of the seventh lens element is concave in a paraxial region thereof and comprises at least one convex shape in an off-axis region thereof;

wherein the image picking-up system further comprises an aperture stop, a central thickness of the seventh lens element is greater than an axial distance between the first lens element and the second lens element, a focal length of the image picking-up system is f, a focal length of the fifth lens element is f5, a maximum among refractive indices of all lens elements of the image picking-up system is Nmax, an axial distance between the aperture stop and the image-side surface of the seventh lens element is SD, an axial distance between the object-side surface of the first lens element and the image-side surface of the seventh lens element is TD, and the following conditions are satisfied:

−1.0 <f/f 5<0.40;

1.60 <N max<1.72; and

0.50 <SD/TD< 1.20.

19. The image picking-up system of claim 18 , wherein the object-side surface of the second lens element is convex in a paraxial region thereof, and the image-side surface of the second lens element is concave in a paraxial region thereof; a maximum among axial distances between each of adjacent lens elements of the image picking-up system is ATmax, a maximum among the central thicknesses of all the lens elements of the image picking-up system is CTmax, and the following condition is satisfied:

0.10< AT max/ CT max<1.0.

20. The image picking-up system of claim 18 , wherein the aperture stop is disposed between the second lens element and the third lens element; each of the seven lens elements is a non-cemented lens element; a f-number of the image picking-up system is Fno, and the following condition is satisfied:

1.20 <Fno< 2.60.

21. The image picking-up system of claim 18 , wherein the focal length of the image picking-up system is f, a focal length of the second lens element is f2, the maximum among the refractive indices of all lens elements of the image picking-up system is Nmax, and the following conditions are satisfied:

−0.20 <f/f 2<0.50; and

1.639 ≤N max<1.72.

22. The image picking-up system of claim 18 , wherein an axial distance between the image-side surface of the seventh lens element and an image surface is BL, an axial distance between the object-side surface of the first lens element and the image surface is TL, an axial distance between the first lens element and the second lens element is T12, a minimum among central thicknesses of all lens elements of the image picking-up system is CTmin, and the following conditions are satisfied:

0.10< BL/TL< 0.35; and

T 12/ CT min<2.50.

23. The image picking-up system of claim 18 , wherein a curvature radius of the object-side surface of the second lens element is R3, a curvature radius of the object-side surface of the third lens element is R5, and the following condition is satisfied:

−2.0<( R 3− R 5)/( R 3+ R 5)≤0.04.