Zoom lens system
View Patent ↗A zoom lens system including, in an order from an object to an image: a first lens group including at least one lens, and a refraction member for bending an optical axis, and having positive refractive power; a second lens group having negative refractive power; a third lens group; and a fourth lens group, wherein zooming is performed by changing at least one interval between the first through fourth lens groups.
1. A zoom lens system comprising, in an order from an object to an image:
a first lens group comprising at least one lens and a refraction member for bending an optical axis, and having positive refractive power;
a second lens group having negative refractive power;
a third lens group; and
a fourth lens group,
wherein zooming is performed by changing at least one interval between the first through fourth lens groups, and the zoom lens system satisfies expressions below:
Fno — w≦ 2.0,
5.5 ≦f T /f W , and
7.5%≦ BFL/OAL,
wherein Fno_w denotes an F-number at a wide-mode, f T denotes an overall focal length at a tele-mode, f W denotes an overall focal length at the wide-mode, BFL denotes a back focal length of the zoom lens system, and OAL denotes an overall length of the zoom lens system from a center of a lens surface of a lens closest to the object to an image plane of the image.
2. The zoom lens system of claim 1 , satisfying an expression below:
13.7%≦ BFL/OAL.
3. The zoom lens system of claim 1 , satisfying an expression below:
BFL≧ 6 mm,
wherein BFL denotes the back focal length at the wide-mode.
4. The zoom lens system of claim 1 , satisfying an expression below:
BFL≧ 8 mm
wherein BFL denotes the back focal length at the wide-mode.
5. The zoom lens system of claim 1 , satisfying an expression below:
OAL≦ 65 mm.
6. The zoom lens system of claim 1 , satisfying an expression below:
1.7 ≦Fno — w≦ 2.0.
7. The zoom lens system of claim 1 , satisfying an expression below:
5.5 ≦f T /f W ≦7.5.
8. The zoom lens system of claim 1 , wherein, when the zooming is performed from the wide-mode to the tele-mode, the second and fourth lens groups move and the first and third lens groups are fixed.
9. The zoom lens system of claim 1 , wherein the third lens group has positive refractive power.
10. The zoom lens system of claim 1 , wherein the fourth lens group has positive refractive power.
11. The zoom lens system of claim 1 , wherein the first lens group comprises at least one aspheric surface.
12. The zoom lens system of claim 1 , wherein the fourth lens group comprises a positive lens and a negative lens in an order from the object to the image.
13. The zoom lens system of claim 12 , wherein a lens of the fourth lens group closest to the object has at least one aspheric surface.
14. The zoom lens system of claim 12 , wherein the positive lens of the fourth lens group satisfies an expression below:
Nd< 1.5,
wherein Nd denotes a refractive index of the positive lens of the fourth lens group.
15. The zoom lens system of claim 1 , wherein the third lens group comprises a cemented lens formed of a positive lens and a negative lens.
16. The zoom lens system of claim 1 , further comprising an aperture disposed between the second lens group and the third lens group.
17. The zoom lens system of claim 1 , wherein the second lens group comprises a plurality of lenses including a first lens closest to the object and a second lens second closest to the object which satisfy an expression below:
1.35 <f 9 /f 11<1.75,
wherein f 9 denotes a focal length of the first lens, and f 11 denotes a focal length of the second lens.
18. The zoom lens system of claim 17 , wherein the second lens is a cemented lens formed of a negative lens and a positive lens.
19. A zoom lens system comprising, in an order from an object to an image:
a first lens group comprising at least one lens, and a refraction member for bending an optical axis, and having positive refractive power;
a second lens group having negative refractive power;
a third lens group; and
a fourth lens group,
wherein zooming is performed by changing at least one interval between the first through fourth lens groups, and a total number of lenses forming the first through fourth lens groups is less than or equal to 10, and
wherein the zoom lens system satisfies an expression below:
BFL≧ 8 mm
wherein BFL denotes the back focal length at the wide-mode.
20. A zoom lens system comprising, in an order from an object to an image:
a first lens group comprising at least one lens, and a refraction member for bending an optical axis, and having positive refractive power;
a second lens group having negative refractive power;
a third lens group; and
a fourth lens group,
wherein zooming is performed by changing at least one interval between the first through fourth lens groups, and a total number of lenses forming the first through fourth lens groups is less than or equal to 10, and
wherein the zoom lens system satisfies an expression below:
Fno — w≦ 2.0, and
7.5%≦ BFL/OAL,
wherein Fno_w denotes an F-number at a wide-mode, BFL denotes a back focal length of the zoom lens system, and OAL denotes an overall length of the zoom lens system from a center of a lens surface of a lens closest to the object to an image plane of the image.