Zoom lens having first through fifth lens groups and a specific focal distance ratio among the lens groups

1. A zoom lens comprising:

a first lens group having a positive refractive power, the first lens group having a focusing function;

a second lens group having a negative refractive power, the second lens group having a variator function of performing zooming;

a third lens group having a positive refractive power, the third lens group having a diaphragm;

a fourth lens group having a positive refractive power, the fourth lens group having a compensator function of correcting a position of an imaging plane at the time of zooming; and

a fifth lens group having one of a positive refractive power and a negative refractive power,

wherein the first, second, third, fourth, and fifth lens groups are sequentially provided from an object side,

wherein the second lens group is moved to the imaging plane side from the object side along an optical axis and the fourth lens group is moved along the optical axis while the first lens group, the third lens group, and the fifth lens group are fixed at the time of zooming from a wide angle end to a telephoto end, and

only the first lens group is moved along the optical axis at the time of focusing, and

the first lens group is composed of three or more lenses including at least one concave lens, and the following formula (1) is satisfied:

0.45<f1 /ft <0.6  (1)

wherein

f1 is a focal distance of the first lens group, and

ft is a focal distance of a total lens system at the telephoto end.

2. The zoom lens according to claim 1 , wherein the fourth lens group includes at least two lenses, and the following formulas (2) to (5) are satisfied:

1< f 4/| f 2|<2.5  (2)

0.83< f 3/ f 4<3  (3)

0.5<β t 4/β w 4<1.7  (4)

β t 4<0.6  (5)

wherein

f2 is a focal distance of the second lens group,

f3 is a focal distance of the third lens group,

f4 is a focal distance of the fourth lens group,

βw4 is lateral magnification of the fourth lens group at the wide angle end, and

βt4 is lateral magnification of the fourth lens group at the telephoto end.

3. The zoom lens according to claim 1 , wherein the fifth lens group includes at least three lenses, and two of the three lenses of the fifth lens group are located at the object side and are configured as a cemented lens composed of a positive lens and a negative lens sequentially from the object side, and the following formula (6) is satisfied:

n 5 B<n 5 A   (6)

wherein

n5A is a d line refractive index of the positive lens included in the cemented lens of the fifth lens group, and

n5B is a d line refractive index of the negative lens included in the cemented lens of the fifth lens group.

4. The zoom lens according to claim 1 , wherein the fourth lens group includes at least two lenses, and the fifth lens group includes at least three lenses, and two of the three lenses of the fifth lens group are located at the object side and are configured as a cemented lens composed of a positive lens and a negative lens sequentially from the object side, and the following formulas (2) to (6) are satisfied:

1< f 4/| f 2|<2.5  (2)

0.83< f 3/ f 4<3  (3)

0.5<β t 4/β w 4<1.7  (4)

β t 4<0.6  (5)

n 5 B<n 5 A   (6)

wherein

f2 is a focal distance of the second lens group,

f3 is a focal distance of the third lens group,

f4 is a focal distance of the fourth lens group,

βw4 is lateral magnification of the fourth lens group at the wide angle end,

βt4 is lateral magnification of the fourth lens group at the telephoto end,

n5A is a d line refractive index of the positive lens included in the cemented lens of the fifth lens group, and

n5B is a d line refractive index of the negative lens included in the cemented lens of the fifth lens group.

5. A zoom lens comprising:

a first lens group having a positive refractive power, the first lens group having a focusing function;

a second lens group having a negative refractive power, the second lens group having a variator function of performing zooming;

a third lens group having a positive refractive power, the third lens group having a diaphragm;

a fourth lens group having a positive refractive power, the fourth lens group having a compensator function of correcting a position of an imaging plane at the time of zooming; and

a fifth lens group having one of a positive refractive power and a negative refractive power,

wherein the first, second, third, fourth, and fifth lens groups are sequentially provided from an object side,

wherein the second lens group is moved to an imaging plane side from the object side along an optical axis and the fourth lens group is moved along the optical axis while the first lens group, the third lens group, and the fifth lens group are fixed at the time of zooming from a wide angle end to a telephoto end, and

only the first lens group is moved along the optical axis at the time of focusing, and

wherein the fourth lens group includes at least two lenses, and the following formulas (2) to (5) are satisfied:

1< f 4/| f 2|<2.5  (2)

0.83< f 3/ f 4<3  (3)

0.5<β t 4/β w 4<1.7  (4)

β t 4<0.6  (5)

wherein

f2 is a focal distance of the second lens group,

f3 is a focal distance of the third lens group,

f4 is a focal distance of the fourth lens group,

βw4 is lateral magnification of the fourth lens group at the wide angle end, and

βt4 is lateral magnification of the fourth lens group at the telephoto end.

6. The zoom lens according to claim 5 ,

wherein the fifth lens group includes at least three lenses, and two of the three lenses of the fifth lens group are located at the object side and are configured as a cemented lens composed of a positive lens and a negative lens sequentially from the object side, and the following formula (6) is satisfied:

n 5 B<n 5 A   (6)

wherein

n5A is a d line refractive index of the positive lens included in the cemented lens of the fifth lens group, and

n5B is a d line refractive index of the negative lens included in the cemented lens of the fifth lens group.

7. A zoom lens comprising:

a first lens group having a positive refractive power, the first lens group having a focusing function;

a second lens group having a negative refractive power, the second lens group having a variator function of performing zooming;

a third lens group having a positive refractive power, the third lens group having a diaphragm;

a fourth lens group having a positive refractive power, the fourth lens group having a compensator function of correcting a position of an imaging plane at the time of zooming; and

a fifth lens group having one of a positive refractive power and a negative refractive power,

wherein the first, second, third, fourth, and fifth lens groups are sequentially provided from an object side,

wherein the second lens group is moved to an imaging plane side from the object side along an optical axis and the fourth lens group is moved along the optical axis while the first lens group, the third lens group, and the fifth lens group are fixed at the time of zooming from a wide angle end to a telephoto end, and

only the first lens group is moved along the optical axis at the time of focusing, and

wherein the first lens group is composed of three or more lenses including at least one concave lens, the fourth lens group includes at least two lenses, and the following formulas (1) and (2) are satisfied:

0.45<f1 /ft < 0 . 6   (1)

1< f 4/| f 2|<2.5  (2)

wherein

f1 is a focal distance of the first lens group,

ft is a focal distance of a total lens system at the telephoto end,

f2 is a focal distance of the second lens group, and

f4 is a focal distance of the fourth lens group.

8. The zoom lens according to claim 7 ,

wherein the following formulas (3) and (4) are satisfied:

0.83< f 3/ f 4<3  (3)

0.5<β t 4/β w 4<1.7  (4)

wherein

f3 is a focal distance of the third lens group,

βw4 is lateral magnification of the fourth lens group at the wide angle end, and

βt4 is lateral magnification of the fourth lens group at the telephoto end.

9. The zoom lens according to claim 8 ,

wherein the fifth lens group includes at least three lenses, and two of the three lenses of the fifth lens group are located at the object side and are configured as a cemented lens composed of a positive lens and a negative lens sequentially from the object side, and the following formula (6) is satisfied:

n 5 B<n 5 A   (6)

wherein

n5A is a d line refractive index of the positive lens included in the cemented lens of the fifth lens group, and

n5B is a d line refractive index of the negative lens included in the cemented lens of the fifth lens group.