Zoom lens, imaging device and camera device and mobile information terminal using the zoom lens

1. A zoom lens, comprising:

a first group optical system having a negative focal length;

a second group optical system having a positive focal length and including at least two positive lenses and at least one negative lens in which one of the two positive lenses is disposed nearest to an object side in the second group optical system;

a third group optical system having a positive focal length,

the first group optical system, the second group optical system and the third group optical system being arranged in this order from the object side to an image side; and

an aperture stop configured to move together with the second group optical system and disposed on the object side of the second group optical system,

a change in magnification being carried out by decreasing a space between the first group optical system and the second group optical system when the change in magnification is carried out from a short focal length end to a long focal length end, wherein

the following formulae are satisfied:

1.95<Nn<2.20

15<νn<35

in which Nn represents a refractive index of a lens with a highest refractive index in the at least one negative lens of the second group optical system, and νn represents an Abbe number of the lens with the highest refractive index in the at least one negative lens of the second group optical system.

2. A zoom lens according to claim 1 , further satisfying the following formula:

−0.02<( r 1 −r 2)/( r 1 +r 2)<0.07

in which r 1 represents a curvature radius of a surface on the object side of the positive lens disposed nearest to the object side in the second group optical system, and r 2 represents a curvature radius of a surface on the image side of the lens with the highest refractive index in the at least one negative lens of the second group optical system.

3. A zoom lens according to claim 1 , further satisfying the following formula:

0.8 <tn/Y ′<1.4

in which tn represents a distance on an optical axis from the surface on the object side of the positive lens disposed nearest to the object side in the second group optical system to the surface on the image side of the lens with the highest refractive index in the at least one negative lens of the second group optical system, and Y′ represents a largest image height.

4. A zoom lens according to claim 1 , wherein the second group optical system includes a cemented lens of a positive lens and a negative lens.

5. A zoom lens according to claim 1 , wherein at least one of the positive lenses of the second group optical system is an aspherical surface.

6. A zoom lens according to claim 5 , wherein the surface on the object side of the positive lens disposed nearest to the object side in the second group optical system includes an aspherical surface.

7. A zoom lens according to claim 1 , further satisfying the following formula:

0.8 <M/f 2<1.5

in which M represents a displacement of the second group optical system, and f 2 represents a focal length of the second group optical system.

8. A zoom lens according to claim 1 , further satisfying the following formula:

0.05 <Nn−Np< 0.3

in which Nn represents the refractive index of the lens with the highest refractive index in the at least one negative lens of the second group optical system, and Np represents a refractive index of the positive lens disposed nearest to the object side in the second group optical system.

9. A zoom lens according to claim 1 , further satisfying the following formula:

−15 <νn−νp<− 5

in which νn represents the Abbe number of the lens with the highest refractive index in the at least one negative lens of the second group optical system, and νp represents an Abbe number of the positive lens disposed nearest to the object side in the second group optical system.

10. A zoom lens according to claim 1 , further satisfying the following formula:

0.8 <ψ/{r 1*tan(ω)}<1.2

in which ψ represents a largest diameter of the aperture stop, ω represents a half-field angle in the short focal length end, and r 1 represents the curvature radius of the surface on the object side of the positive lens disposed nearest to the object side in the second group optical system.

11. A zoom lens according to claim 1 , wherein the third group optical system comprises a spherical lens.

12. An imaging device, including a zoom lens comprising:

a first group optical system having a negative focal length;

a second group optical system having a positive focal length and including at least two positive lenses and at least one negative lens in which one of the two positive lenses is disposed nearest to an object side in the second group optical system;

a third group optical system having a positive focal length,

the first group optical system, the second group optical system and the third group optical system being arranged in this order from the object side to an image side; and

an aperture stop configured to move together with the second group optical system and disposed on the object side of the second group optical system,

a change in magnification being carried out by decreasing a space between the first group optical system and the second group optical system when the change in magnification is carried out from a short focal length end to a long focal length end, wherein

the following formulae are satisfied:

1.95<Nn<2.20

15<νn<35

in which Nn represents a refractive index of a lens with a highest refractive index in the at least one negative lens of the second group optical system, and νn represents an Abbe number of the lens with the highest refractive index in the at least one negative lens of the second group optical system.

13. A camera device, including a zoom lens comprising:

a first group optical system having a negative focal length;

a second group optical system having a positive focal length and including at least two positive lenses and at least one negative lens in which one of the two positive lenses is disposed nearest to an object side in the second group optical system;

a third group optical system having a positive focal length,

the first group optical system, the second group optical system and the third group optical system being arranged in this order from the object side to an image side; and

an aperture stop configured to move together with the second group optical system and disposed on the object side of the second group optical system,

a change in magnification being carried out by decreasing a space between the first group optical system and the second group optical system when the change in magnification is carried out from a short focal length end to a long focal length end, wherein

the following formulae are satisfied:

1.95<Nn<2.20

15<νn<35

in which Nn represents a refractive index of a lens with a highest refractive index in the at least one negative lens of the second group optical system, and νn represents an Abbe number of the lens with the highest refractive index in the at least one negative lens of the second group optical system.

14. A camera device according to claim 13 , wherein the camera device has a function of converting a photographed image into digital data.

15. A camera device according to claim 14 , further comprising a light-receiving element configured to receive an image captured by the zoom lens, and having pixels equal to or more than three million.

16. A mobile information terminal, including a zoom lens comprising:

a first group optical system having a negative focal length;

a second group optical system having a positive focal length and including at least two positive lenses and at least one negative lens in which one of the two positive lenses is disposed nearest to an object side in the second group optical system;

a third group optical system having a positive focal length,

the first group optical system, the second group optical system and the third group optical system being arranged in this order from the object side to an image side; and

an aperture stop configured to move together with the second group optical system and disposed on the object side of the second group optical system,

a change in magnification being carried out by decreasing a space between the first group optical system and the second group optical system when the change in magnification is carried out from a short focal length end to a long focal length end, wherein

the following formulae are satisfied:

1.95<Nn<2.20

15<νn<35

in which Nn represents a refractive index of a lens with a highest refractive index in the at least one negative lens of the second group optical system, and νn represents an Abbe number of the lens with the highest refractive index in the at least one negative lens of the second group optical system.