Zoom lens system, imaging device and camera

1. A zoom lens system having a plurality of lens units, each lens unit being composed of at least one lens element, the zoom lens system, in order from an object side to an image side, comprising:

a first lens unit having negative optical power;

a second lens unit having positive optical power; and

a third lens unit having positive optical power, wherein

the first lens unit is located object-side-most among the plurality of lens units in the entire zoom lens system,

in zooming from a wide-angle limit to a telephoto limit at the time of image taking, the first lens unit, the second lens unit, and the third lens unit are individually moved along an optical axis to vary magnification,

each of the first lens unit, the second lens unit, and the third lens unit includes at least one lens element that satisfies the following conditions (1), (2) and (3), and

the following condition (4) is satisfied:

nd≦ 1.67  (1)

vd< 59  (2)

0.000< PgF+ 0.002× vd− 0.664  (3)

0.31< Ir /√(| f G1 ×f G2 |)  (4)

where

nd is a refractive index to the d-line of the lens element,

vd is an Abbe number to the d-line of the lens element,

PgF is a partial dispersion ratio of the lens element, which is the ratio of a difference between a refractive index to the g-line and a refractive index to the F-line, to a difference between a refractive index to the F-line and a refractive index to the C-line,

Ir is a maximum image height (Ir=f T ×tan(ω T )),

f T is a focal length of the entire system at a telephoto limit,

ω T is a half value (°) of maximum view angle at a telephoto limit,

f G1 is a focal length of the first lens unit, and

f G2 is a focal length of the second lens unit.

2. The zoom lens system as claimed in claim 1 , wherein the first lens unit is composed of two lens elements each having optical power.

3. The zoom lens system as claimed in claim 2 , wherein the following condition (8) is satisfied:

D 12 /D L1 >3.9  (8)

where

D 12 is an air space between a first lens element located on the object side and a second lens element located on the image side, in the first lens unit, and

D L1 is an optical axial thickness of the first lens element.

4. The zoom lens system as claimed in claim 1 , wherein the second lens unit is composed of three lens elements each having optical power.

5. The zoom lens system as claimed in claim 1 , wherein the third lens unit is composed of one lens element.

6. The zoom lens system as claimed in claim 1 , wherein a first lens element located on the most object side in the first lens unit satisfies the following condition (5):

nd L1 <1.80  (5)

where

nd L1 is a refractive index to the d-line of the first lens element.

7. The zoom lens system as claimed in claim 1 , wherein a second lens element located on the most image side in the first lens unit satisfies the following condition (6):

nd L2 <1.80  (6)

where

nd L2 is a refractive index to the d-line of the second lens element.

8. The zoom lens system as claimed in claim 1 , wherein the following condition (7) is satisfied:

D G1 /f T <0.193  (7)

where

D G1 is an optical axial thickness of the first lens unit, and

f T is a focal length of the entire system at a telephoto limit.

9. The zoom lens system as claimed in claim 1 , wherein the following condition (9) is satisfied:

f G2 /f T <0.5  (9)

where

f G2 is a focal length of the second lens unit, and

f T is a focal length of the entire system at a telephoto limit.

10. The zoom lens system as claimed in claim 1 , wherein the following condition (10) is satisfied:

nd AVE <1.70  (10)

where

nd AVE is an average of refractive indices to the d-line of the lens elements each having optical power in the entire system.

11. The zoom lens system as claimed in claim 1 , wherein the following condition (11) is satisfied:

nd 1AVE <1.70  (11)

where

nd 1AVE is an average of refractive indices to the d-line of the lens elements constituting the first lens unit.

12. The zoom lens system as claimed in claim 1 , wherein a lens element located on the most image side in the second lens unit satisfies the following condition (12):

nd 23 <1.65  (12)

where

nd 23 is a refractive index to the d-line of the lens element located on the most image side in the second lens unit.

13. The zoom lens system as claimed in claim 1 , wherein the following condition (13) is satisfied:

L W /L T <1.0  (13)

where

L W is an overall length of lens system at a wide-angle limit, and

L T is an overall length of lens system at a telephoto limit.

14. The zoom lens system as claimed in claim 1 , wherein the second lens unit moves in a direction perpendicular to the optical axis to optically compensate image blur.

15. An imaging device capable of outputting an optical image of an object as an electric image signal, comprising:

a zoom lens system that forms an optical image of the object; and

an image sensor that converts the optical image formed by the zoom lens system into the electric image signal, wherein

the zoom lens system is a zoom lens system as claimed in claim 1 .

16. A camera for converting an optical image of an object into an electric image signal and then performing at least one of displaying and storing of the converted image signal, comprising:

an imaging device including a zoom lens system that forms an optical image of the object, and an image sensor that converts the optical image formed by the zoom lens system into the electric image signal, wherein

the zoom lens system is a zoom lens system as claimed in claim 1 .