Zoom lens system, interchangeable lens, and imaging apparatus
A zoom lens satisfies Conditional Expression (1) as follows: −20< Twt/Twm <1, (1) Twt is a moving amount of the second lens group during zooming from the short focal-length end to the long focal-length end, a moving amount to the object side being indicated by a positive sign, a moving amount to an image side being indicated by a negative sign, and Twm is a moving amount of the second lens group during zooming from the short focal-length end to an intermediate focal length, a moving amount to the image side being indicated by a negative sign, the intermediate focal length being expressed by fm=(fw·ft) 1/2 , where fw is a focal length of a whole system at the short focal-length end, and ft is a focal length of the whole system at the long focal-length end.
1. A zoom lens system comprising:
sequentially from an object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a negative refractive power, and a rear lens group having a positive refractive power,
wherein distances among the respective lens groups adjacent to one another change during zooming from a short focal-length end to a long focal-length end,
wherein the third lens group constitutes a focus lens group configured to move during focusing,
wherein the rear lens group includes an N-th lens group having a negative refractive power and configured such that distances between the N-th lens group and the respective lens groups adjacent to the N-th lens group change during zooming from the short focal-length end to the long focal-length end, and
wherein the zoom lens system satisfies Conditional Expression (1) as follows:
−20< Twt/Twm< 1, (1)
where
Twt is a moving amount of the second lens group during zooming from the short focal-length end to the long focal-length end, a moving amount to the object side being indicated by a positive sign, a moving amount to an image side being indicated by a negative sign, and
Twm is a moving amount of the second lens group during zooming from the short focal-length end to an intermediate focal length, a moving amount to the object side being indicated by a positive sign, a moving amount to the image side being indicated by a negative sign,
the intermediate focal length being expressed by fm=(fw-ft) 1/2 , where fw is a focal length of a whole system at the short focal-length end, and ft is a focal length of the whole system at the long focal-length end.
2. The zoom lens system according to claim 1 , wherein the zoom lens system satisfies Conditional Expression (2) as follows:
2.0< frw/Ya< 3.5, (2)
where
frw is a focal length of the rear lens group at the short focal-length end in focus at infinity, and
Ya is a maximum image height.
3. The zoom lens system according to claim 1 , wherein the zoom lens system satisfies Conditional Expressions (3) and (4) as follows:
2.0<| f 3/ ffw|< 5.0, and (3)
1.0<| f 3/ fft|< 4.0, (4)
where
f3 is a focal length of the third lens group,
ffw is a composite focal length of the first lens group, the second lens group, and the third lens group at the short focal-length end in focus at infinity, and
fft is a composite focal length of the first lens group, the second lens group, and the third lens group at the long focal-length end in focus at infinity.
4. The zoom lens system according to claim 1 , wherein the zoom lens system satisfies Conditional Expression (5) as follows:
0.1< f 2/ f 3<0.7, (5)
where
f2 is a focal length of the second lens group, and
f3 is a focal length of the third lens group.
5. The zoom lens system according to claim 1 , wherein the third lens group includes two lenses of a negative lens and a positive lens.
6. The zoom lens system according to claim 1 , wherein the zoom lens system satisfies Conditional Expression (6) as follows:
0.1< R 3 gf/R 2 gr< 5.0, (6)
where
R3gf is a curvature radius of a surface disposed closest to the object side of the third lens group, and
R2gr is a curvature radius of a surface disposed closest to the image side of the second lens group.
7. The zoom lens system according to claim 1 , wherein the zoom lens system satisfies Conditional Expression (7) as follows:
1.5< Bfw/Ya< 4.0, (7)
where
Bfw is a distance in terms of air conversion from a surface disposed closest to the image side of the rear lens group at the short focal-length end in focus at infinity to the image surface, and
Ya is the maximum image height.
8. The zoom lens system according to claim 1 , wherein the zoom lens system satisfies Conditional Expression (8) as follows:
1.5< Bfw/fw< 4.0, (8)
where
Bfw is a distance in terms of air conversion from the surface disposed closest to the image side of the rear lens group at the short focal-length end in focus at infinity to the image surface, and
fw is a focal length of the whole system at the short focal-length end in focus at infinity.
9. The zoom lens system according to claim 1 , wherein the zoom lens system satisfies Conditional Expression (9) as follows:
2.5< f 1/ fw< 6.0, (9)
where
f1 is a focal length of the first lens group, and
fw is a focal length of the whole system at the short focal-length end in focus at infinity.
10. The zoom lens system according to claim 1 , wherein one of the second lens group and the third lens group includes at least one positive lens, and wherein the zoom lens system satisfies Conditional Expression (10) as follows:
25<ν p MAX<45, (10)
where
νpMAX is an Abbe number for a d-line of a positive lens having a largest Abbe number and included in the at least one positive lens included in the one of the second lens group and the third lens group.
11. The zoom lens system according to claim 1 , wherein the first lens group moves from an image side toward the object side during zooming from the short focal-length end to the long focal-length end, wherein the zoom lens system satisfies Conditional Expression (11) as follows:
1.5< f 1/ Twt 1<7.0, (11)
where
f1 is a focal length of the first lens group, and
Twt1 is a moving amount of the first lens group during zooming from the short focal-length end to the long focal-length end, a moving amount to the object side being indicated by a positive sign, a moving amount to the image side being indicated by a negative sign.
12. The zoom lens system according to claim 1 , wherein the zoom lens system satisfies Conditional Expression (12) as follows:
−20.0< f 1/ f 23 w <−3.0, (12)
where
f1 is a focal length of the first lens group, and
f23w is a composite focal length of the second lens group and the third lens group at the short focal-length end in focus at infinity.
13. The zoom lens system according to claim 1 , wherein the zoom lens system satisfies Conditional Expression (13) as follows:
0.20< D (2 R− 3 F ) T/D (2 F− 3 R ) T< 0.60, (13)
where
D(2R−3F)T is a distance in an optical-axis direction from a final surface of the second lens group to a foremost surface of the third lens group at the long focal-length end in focus at infinity, and
D(2F−3R)T is a total thickness in the optical-axis direction from a foremost surface of the second lens group to a surface disposed closest to the image surface of the third lens group at the long focal-length end in focus at infinity.
14. The zoom lens system according to claim 1 , wherein the zoom lens system satisfies Conditional Expression (14) as follows:
1.00<(1 −Mt{circumflex over ( )} 2)× MRt{circumflex over ( )} 2<8.00, (14)
where
Mt is a lateral magnification of the third lens group at the long focal-length end in focus at infinity, and
MRt is a lateral magnification of the rear lens group at the long focal-length end in focus at infinity.
15. The zoom lens system according to claim 1 , wherein the zoom lens system has an F-number of less than or equal to 3 over a whole focal-length range.
16. The zoom lens system according to claim 1 , wherein the rear lens group includes, sequentially from the object side, a fourth lens group having a positive refractive power, a fifth lens group having a negative refractive power and serving as the N-th lens group, and a sixth lens group having a positive refractive power.
17. An interchangeable lens comprising:
the zoom lens system according to claim 1 .
18. An imaging apparatus comprising:
the zoom lens system according to claim 1 .