Fisheye lens system and photographing apparatus
View Patent ↗A fisheye lens system and a photographing apparatus including the fisheye lens system. The fisheye lens system includes, in an order from an object to an image, a first lens group including at least three lenses and having negative refractive power; and a second lens group having positive refractive power, wherein the at least three lenses included in the first lens group include a first lens, a second lens, and a third lens, in the order from the object to the image.
1. A fisheye lens system comprising, in an order from an object to an image:
a first lens group comprising at least three lenses and having negative refractive power;
a second lens group having positive refractive power; and
an aperture disposed between the first lens group and the second lens group,
wherein the at least three lenses included in the first lens group comprise a first lens, a second lens, and a third lens, in the order from the object to the image, and satisfy conditions below:
0.4 <SF 1<0.6;
0.5 <SF 2<1.0; and
1.3 <SF 3<5.5, and
wherein SFi=(R 1 i −R 2 i )/(R 1 i +R 2 i ) is a shaping factor of an i th lens (I=1, 2, or 3), R 1 i is a radius of curvature of a surface of an object side of the i th lens, and R 2 i is a radius of curvature of a surface of an image side of the i th lens, and
wherein the second lens group comprises an aspheric lens.
2. The fisheye lens system of claim 1 , wherein the first lens group satisfies a condition below:
−0.4 <f/fl<− 0.2
wherein f denotes an overall focal length of the fisheye lens system, and fl denotes a focal length of the first lens group.
3. The fisheye lens system of claim 1 , wherein the first lens group further comprises a fourth lens having positive refractive power.
4. The fisheye lens system of claim 1 , wherein the second lens group comprises four lenses.
5. The fisheye lens system of claim 1 , wherein the second lens group comprises a positive lens, a positive lens, a negative lens, and a positive lens.
6. The fisheye lens system of claim 1 , wherein the second lens group comprises a cemented lens.
7. A photographing apparatus comprising:
the fisheye lens system of claim 1 ; and
an imaging sensor which converts light formed by the fisheye lens system into an electrical image signal.
8. The fisheye lens system of claim 1 , wherein the first lens satisfies a condition below:
1.3 <H 1/2 Y< 1.5,
wherein H 1 denotes an effective radius of the surface of the object side of the first lens and 2 Y denotes a diameter of an image circle.
9. The fisheye lens system of claim 8 , wherein the first lens group satisfies a condition below:
−0.4 <f/fl<− 0.2,
wherein f denotes an overall focal length of the fisheye lens system, and fl denotes a focal length of the first lens group.
10. The fisheye lens system of claim 1 , wherein each of the first lens, the second lens, and the third lens has negative refractive power.
11. The fisheye lens system of claim 10 , wherein each of the first lens and the second lens is a meniscus lens having a surface convex toward the object.
12. The fisheye lens system of claim 1 , wherein an interval D between the first lens group and the second lens group satisfies a condition below:
0.3 <D/Ds< 0.5,
wherein Ds denotes a length between a lens surface that is closest to the object and a lens surface that is close to the image in the fisheye lens system.
13. The fisheye lens system of claim 12 , wherein the first lens satisfies a condition below:
1.3 <H 1/2 Y< 1.5,
wherein H 1 denotes an effective radius of the surface of the object side of the first lens and 2 Y denotes a diameter of an image circle.
14. The fisheye lens system of claim 13 , wherein the first lens group satisfies a condition below:
−0.4 <f/fl<− 0.2,
wherein f denotes an overall focal length of the fisheye lens system, and fl denotes a focal length of the first lens group.
15. The fisheye lens system of claim 1 , wherein an interval D between the first lens group and the second lens group satisfies a condition below:
3.0 <D/f< 4.0,
wherein f denotes an overall focal length of the fisheye lens system.
16. The fisheye lens system of claim 15 , wherein the interval D further satisfies a condition below:
0.3 <D/Ds < 0.5,
wherein Ds denotes a length between a lens surface that is closest to the object and a lens surface that is close to the image in the fisheye lens system.
17. The fisheye lens system of claim 16 , wherein the first lens satisfies a condition below:
1.3 <H 1/2 Y< 1.5,
wherein H 1 denotes an effective radius of the surface of the object side of the first lens and 2 Y denotes a diameter of an image circle.
18. The fisheye lens system of claim 17 , wherein the first lens group satisfies a condition below:
−0.4 <f/fl<− 0.2,
wherein f denotes an overall focal length of the fisheye lens system, and fl denotes a focal length of the first lens group.