Photographic optical system

1. A photographic optical system, comprising, from an object side to an image side: a first lens, a second lens, a third lens, a fourth lens, a fifth lens and a sixth lens arranged coaxially and satisfying the following relational expressions:

0.8< f 1/ f< 1.2

−8< f 2/ f<− 1

400< f 3/ f< 600

5< f 4/ f< 18

0.1< f 5/ f< 1

−1< f 6/ f<− 0.1

where

f1 denotes a focal length of the first lens;

f2 denotes a focal length of the second lens;

f3 denotes a focal length of the third lens;

f4 denotes a focal length of the fourth lens;

f5 denotes a focal length of the fifth lens;

f6 denotes a focal length of the sixth lens; and

f denotes an overall focal length of the photographic optical system.

2. The photographic optical system as described in claim 1 , wherein the first lens has an object side surface being convex near an axis and an image side surface being concave near the axis and satisfies the following relational expressions:

4.9< f 1<5.2

1.58< n 1<1.7

58< v 1<62

where

n1 denotes a refraction index of the first lens; and

v1 denotes an abbe number of the first lens.

3. The photographic optical system as described in claim 1 , wherein the second lens has an object side surface being convex near an axis and satisfies the following relational expressions:

−17.5< f 2<−14

1.64< n 2<1.68

19< v 2<22

where

n2 denotes a refraction index of the second lens; and

v2 denotes an abbe number of the second lens.

4. The photographic optical system as described in claim 1 , wherein the third lens has an object side surface being convex near an axis and satisfies the following relational expressions:

2000< f 3<2400

1.52< n 3<1.56

54< v 3<58

where

n3 denotes a refraction index of the third lens; and

v3 denotes an abbe number of the third lens.

5. The photographic optical system as described in claim 1 , wherein the fourth lens has an object side surface being convex near an axis and satisfies the following relational expressions:

70< f 4<76

1.62< n 4<1.66

23< v 4<25

where

n4 denotes a refraction index of the fourth lens; and

v4 denotes an abbe number of the fourth lens.

6. The photographic optical system as described in claim 1 , wherein the fifth lens has a positive refractive power, has an object side surface being concave near an axis and an image side surface being convex near the axis, and satisfies the following relational expressions:

3.5< f 5<3.9

1.52< n 5<1.56

52< v 5<58

where

n5 denotes a refraction index of the fifth lens; and

v5 denotes an abbe number of the fifth lens.

7. The photographic optical system as described in claim 1 , wherein the sixth lens has an object side surface being concave near an axis and satisfies the following relational expressions:

−3.2< f 6<−2.8

1.52< n 6<1.54

54< v 6<58

where

n6 denotes a refraction index of the sixth lens; and

v6 denotes an abbe number of the sixth lens.

8. The photographic optical system as described in claim 1 , wherein the photographic optical system has a Total Track Length (TTL) smaller than or equal to 5.6 millimeters.

9. The photographic optical system as described in claim 1 , wherein the photographic optical system has an aperture F-number smaller than or equal to 1.45.

10. The photographic optical system as described in claim 1 , wherein the first lens is a glass lens.