Variable magnification optical system, optical apparatus and method for manufacturing variable magnification optical system

1. A variable power optical system comprising, in order from an object toward an image on an image side:

a first lens group having positive refractive power;

a second lens group having negative refractive power;

a third lens group having positive refractive power; and

a fourth lens group having positive or negative refractive power,

a distance between the first lens group and the second lens group, a distance between the second lens group and the third lens group, and a distance between the third lens group and the fourth lens group changing respectively upon zooming from a wide-angle end state to a telephoto end state,

the third lens group comprising, in order from the object, a first positive lens, a second positive lens, a first negative lens, a second negative lens and a third positive lens,

the third or the fourth lens group including a focusing group which is moved along an optical axis upon focusing, and

the focusing group consisting of a negative meniscus lens having a concave surface facing the image.

2. The variable power optical system according to claim 1 , wherein a positive lens is provided next to the focusing group on the image side.

3. The variable power optical system according to claim 1 , wherein the focusing group satisfies the following conditional expressions:

ndF+ 0.0052×ν dF− 1.965<0

ν dF> 60

where ndF denotes a refractive index of a medium of the negative lens included in the focusing group at d-line, and νdF denotes an Abbe number of the medium of the negative meniscus lens included in the focusing group.

4. The variable power optical system according to claim 1 , wherein the first positive lens satisfies the following conditional expression:

ν dO> 60

where νdO denotes an Abbe number of a medium of the first positive lens.

5. The variable power optical system according to claim 1 , wherein the second lens group comprises, in order from the object, a negative lens, a negative lens, a positive lens and a negative lens.

6. The variable power optical system according to claim 1 , wherein the second lens group moves toward the image at first and then moves toward the object upon zooming from the wide-angle end state to the telephoto end state.

7. The variable power optical system according to claim 1 , wherein the focusing group is placed next to the third positive lens on the image side, and a distance between the third positive lens and the focusing group changes upon zooming.

8. The variable power optical system according to claim 1 , wherein a third negative lens, a fourth positive lens and a fourth negative lens are provided next to the third positive lens on the image side.

9. The variable power optical system according to claim 1 , wherein the following conditional expression is satisfied:

0.9< f 3/( fw×ft ) 1/2 <2.0

where f3 denotes a focal length of the third lens group, fw denotes a focal length of the variable power optical system in the wide-angle end state, and ft denotes a focal length of the variable power optical system in the telephoto end state.

10. An optical apparatus comprising the variable power optical system according to claim 1 .

11. A variable power optical system comprising, in order from an object:

a first lens group having positive refractive power;

a second lens group having negative refractive power;

a third lens group having positive refractive power; and

a fourth lens group having positive or negative refractive power,

a distance between the first lens group and the second lens group, a distance between the second lens group and the third lens group and a distance between the third lens group and the fourth lens group changing respectively upon zooming from a wide-angle end state to a telephoto end state,

the third lens group including, in order from the object, a first positive lens, a second positive lens, a first negative lens, a second negative lens and a third positive lens, and

the third lens group including a focusing group which is moved along an optical axis upon focusing.

12. The variable power optical system according to claim 11 , wherein the third lens group comprises a vibration-isolating lens group which can move so as to have a movement component in a direction orthogonal to the optical axis upon correcting camera shake.

13. The variable power optical system according to claim 12 , wherein the vibration-isolating lens group consists of one cemented lens.

14. The variable power optical system according to claim 12 , wherein the vibration-isolating lens group consists of one negative lens and one positive lens.

15. The variable power optical system according to claim 11 , wherein the following conditional expression is satisfied:

0.9< f 3/( fw×ft ) 1/2 <2.0

where f3 denotes a focal length of the third lens group, fw denotes a focal length of the variable power optical system in the wide-angle end state, and ft denotes a focal length of the variable power optical system in the telephoto end state.

16. The variable power optical system according to claim 11 , wherein the first positive lens satisfies the following conditional expression:

ν dO> 60

where νdO denotes an Abbe number of a medium of the first positive lens.

17. An optical apparatus comprising the variable power optical system according to claim 11 .

18. A variable power optical system consisting of, in order from an object:

a first lens group having positive refractive power;

a second lens group having negative refractive power;

a third lens group having positive refractive power; and

a fourth lens group having positive or negative refractive power,

a distance between the first lens group and the second lens group, a distance between the second lens group and the third lens group and a distance between the third lens group and the fourth lens group changing respectively upon zooming from a wide-angle end state to a telephoto end state,

the third lens group comprising, in order from the object, a first positive lens, a second positive lens, a first negative lens, a second negative lens and a third positive lens,

the third or the fourth lens group including a focusing group which is moved along an optical axis upon focusing, and

the focusing group having negative refractive power.

19. A method of manufacturing a variable power optical system, comprising:

arranging, in order from an object, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power; and a fourth lens group having positive or negative refractive power,

the lens groups being arranged such that a distance between the first lens group and the second lens group, a distance between the second lens group and the third lens group and a distance between the third lens group and the fourth lens group change respectively upon zooming from a wide-angle end state to a telephoto end state, and

the third lens group comprising, in order from the object, a first positive lens, a second positive lens, a first negative lens, a second negative lens and a third positive lens,

the method further comprising one of the following features (A), (B) or (C):

the feature (A) including:

configuring the third or the fourth lens group to include a focusing group which is moved along an optical axis upon focusing,

the focusing group consisting of a negative meniscus lens having a concave surface facing the image,

the feature (B) including:

configuring the third lens group to include a focusing group which is moved along an optical axis upon focusing,

the feature (C) including:

configuring the variable power optical system to consist of the first to the fourth lens groups, and

configuring the third or the fourth lens group to include a focusing group which is moved along an optical axis upon focusing,

the focusing group having negative refractive power.