Variable magnification optical system, optical equipment, and method for producing variable magnification optical system

1 . A variable magnification optical system comprising, in order from an object side, a first lens group having negative refractive power, a second lens group having positive refractive power, a third lens group and a fourth lens group;

upon varying a magnification, respective distances between neighboring lens groups being varied;

the first lens group comprising a negative lens at a most object side and a positive lens at a most image side;

the negative lens at the most object side in the first lens group being a negative meniscus lens having a convex surface facing the object side;

the second lens group comprising, in order from the object side, a 2a lens group having positive refractive power, a 2b lens group having positive refractive power and a 2c lens group; and

the following conditional expressions being satisfied:

0.05

<

f

⁢

21

/

f

⁢

22

<

3.

⁢

0.35

<

(

-

f

⁢

23

)

/

f

⁢

t

<

2.8

1.1

<

f

⁢

12

/

(

-

f

⁢

1

)

<

4.

0.1

<

G

⁢

2

/

TLt

<

0.5

where f21 denotes a focal length of the 2a lens group, f22 denotes a focal length of the 2b lens group, f23 denotes a focal length of the 2c lens group, ft denotes a focal length of the variable magnification optical system as a whole in a telephoto end state, f12 denotes a focal length of the positive lens, f1 denotes a focal length of the first lens group, G 2 denotes a length of the second lens group on an optical axis, and TLt denotes a length of the variable magnification optical system as a whole on the optical axis in the telephoto end state.

2 . A variable magnification optical system according to claim 1 , wherein the following conditional expression is satisfied:

50.

°

<

2

⁢

ω

<

120.

°

where 2ω denotes an entire angle of view of the variable magnification optical system in a wide angle end state.

3 . A variable magnification optical system according to claim 1 , wherein the following conditional expression is satisfied:

0.5

<

(

-

f

⁢

3

)

/

fw

<

3.

where f3 denotes a focal length of the third lens group and fw denotes a focal length of the variable magnification optical system as a whole in a wide angle end state.

4 . A variable magnification optical system according to claim 1 , wherein the following conditional expression is satisfied:

0.02

<

G4

/

TLt

<

0.2

where G 4 denotes a length of the fourth lens group on the optical axis.

5 . A variable magnification optical system according to claim 1 , wherein the following conditional expression is satisfied:

0.2

<

Bfa

/

fw

<

0.9

where Bfa denotes an air converted back focus of the variable magnification optical system as a whole in a wide angle end state and fw denotes a focal length of the variable magnification optical system as a whole in the wide angle end state.

6 . A variable magnification optical system according to claim 1 , wherein the following conditional expression is satisfied:

0.2

<

f

⁢

22

/

f

⁢

t

<

1.7

.

7 . An optical equipment comprising a variable magnification optical system according to claim 1 .

8 . A method for manufacturing a variable magnification optical system comprising, in order from an object side, a first lens group having negative refractive power, a second lens group having positive refractive power, a third lens group and a fourth lens group, the method comprising:

constructing such that, upon varying a magnification, respective distances between neighboring lens groups are varied;

constructing such that the first lens group comprises a negative lens at a most object side and a positive lens at a most image side;

the negative lens at the most object side in the first lens group being a negative meniscus lens having a convex surface facing the object side;

constructing such that the second lens group comprises, in order from the object side, a 2a lens group having positive refractive power, a 2b lens group having positive refractive power and a 2c lens group; and

constructing such that the following conditional expressions are satisfied:

0.05

<

f

⁢

21

/

f

⁢

22

<

3.

⁢

0.35

<

(

-

f

⁢

23

)

/

f

⁢

t

<

2.8

1

.

1

⁢

0

<

f

⁢

12

/

(

-

f

⁢

1

)

<

4.

0.

1

⁢

0

⁢

0

<

G

⁢

2

/

T

⁢

L

⁢

t

<

0.5

where f21 denotes a focal length of the 2a lens group, f22 denotes a focal length of the 2b lens group, f23 denotes a focal length of the 2c lens group, ft denotes a focal length of the variable magnification optical system as a whole in a telephoto end state, f12 denotes a focal length of the positive lens, f1 denotes a focal length of the first lens group, G 2 denotes a length of the second lens group on an optical axis, and TLt denotes a length of the variable magnification optical system as a whole on the optical axis in the telephoto end state.