Zoom lens system
View Patent ↗A zoom lens system including, in an order from an object to an image: a first lens group having negative refractive power; and a second lens group having positive refractive power, wherein the zoom lens system satisfies equations: i) 1.2≦F now ≦2.2; ii) 2.5<f t /f w ≦3; and iii) BFL≧6 mm, where F now denotes an F-number at a wide angle position, f t and f w respectively denotes overall focal lengths at a telephoto position and the wide angle position, and BFL denotes a back focal length.
1. A zoom lens system comprising, in an order from an object to an image:
a first lens group having negative refractive power; and
a second lens group having positive refractive power,
wherein the zoom lens system satisfies conditions below:
1.2≦ F now ≦2.2;
2.5< f t /f w ≦3; and
BFL≧6 mm,
wherein F now denotes an F-number at a wide angle position, f t and f w respectively denotes overall focal lengths at a telephoto position and a wide angle position, and BFL denotes a back focal length,
wherein the condition −3.0< f I /f w <−2.5 is satisfied, and
wherein f I denotes a focal length of the first lens group and f w denotes the overall focal length at the wide angle position.
2. The zoom lens system of claim 1 , wherein the first lens group and the second lens group move such that an interval between the first lens group and the second lens group changes while zooming from the wide angle position to the telephoto position.
3. The zoom lens system of claim 2 , wherein the first lens group moves toward the image and the second lens group moves toward the object while the zooming from the wide angle position to the telephoto position.
4. The zoom lens system of claim 1 , wherein an iris is disposed between the first lens group and the second lens group, and the iris is fixed and does not move during zooming.
5. The zoom lens system of claim 1 , wherein the first lens group comprises, in an order from the object to the image:
a first lens having negative refractive power;
a second lens having negative refractive power; and
a third lens having positive refractive power.
6. The zoom lens system of claim 5 , wherein the second lens group comprises, in an order from the object to the image:
a fourth lens having positive refractive power;
a fifth lens having negative refractive power; and
a sixth lens having positive refractive power.
7. The zoom lens system of claim 6 , wherein the second lens group comprises at least one aspheric surface.
8. The zoom lens system of claim 7 , wherein a lens surface of the second lens group closest to the image is an aspheric surface.
9. The zoom lens system of claim 8 , wherein a lens surface of the second lens group closest to the object is an aspheric surface.
10. The zoom lens system of claim 7 , wherein a lens surface of the second lens group closest to the object is an aspheric surface.
11. The zoom lens system of claim 6 , wherein the fifth and sixth lenses are formed as a cemented lens.
12. The zoom lens system of claim 5 , wherein the second and third lenses are formed as a cemented lens.
13. An imaging apparatus comprising:
a zoom lens system of claim 1 ; and
an image pickup device for converting an optical image formed by the zoom lens system to an electric signal.
14. A zoom lens system comprising, in an order from an object to an image:
a first lens group having negative refractive power; and
a second lens group having positive refractive power,
wherein the zoom lens system satisfies conditions below:
1.2 ≦F now ≦2.2;
2.5< f t /f w <3; and
BFL≧6 mm,
wherein F now denotes an F-number at a wide angle position, f t and f w respectively denotes overall focal lengths at a telephoto position and a wide angle position, and BFL denotes a back focal length,
wherein the condition vd 22 <30 is satisfied, and
wherein vd 22 denotes an Abbe number of a second lens from the object in the second lens group.
15. The zoom lens system of claim 14 ,
wherein a condition v(G 2 +)>50 is satisfied, and
wherein v(G 2 +) denotes an average of Abbe numbers of lenses having positive refractive power in the second lens group.
16. The zoom lens system of claim 15 ,
wherein a condition nd 21 >1.58 is satisfied, and
wherein nd 21 denotes a d-line refractive index of the first lens from the object in the second lens group.
17. The zoom lens system of claim 14 ,
wherein a condition nd 21 >1.58 is satisfied, and
wherein nd 21 denotes a d-line refractive index of the first lens from the object in the second lens group.
18. A zoom lens system comprising, in an order from an object to an image:
a first lens group having negative refractive power; and
a second lens group having positive refractive power,
wherein the zoom lens system satisfies conditions below:
1.2 ≦F now ≦2.2;
2.5< f t /f w ≦3; and
BFL≧6 mm,
wherein F now denotes an F-number at a wide angle position, f t and f w respectively denotes overall focal lengths at a telephoto position and a wide angle position, and BFL denotes a back focal length,
wherein a condition v(G 2 +)>50 is satisfied, and
wherein v(G 2 +) denotes an average of Abbe numbers of lenses having positive refractive power in the second lens group.