Zoom lens capable of image stabilization and imaging apparatus
A zoom lens capable of image stabilization is provided and includes: in order from the object side, a positive first group fixed in variable magnification, a negative second group having a variable magnification function, a positive third group fixed in variable magnification, and a positive fourth group having a correction function for an image plane variation depending upon variable magnification and a focusing function. In the third group, there are arranged a positive 3a-th group, a negative 3b-th group, and a positive 3c-th group in this order from the object side. Blurring of a taken image caused by a vibration of this variable magnification optical system is corrected by moving the 3b-th group in a direction approximately orthogonal to the optical axis. Further, a specific conditional expression relating to power of the third group and a specific conditional expression relating to a power distribution of lens groups of the third group G 3 are satisfied.
1. A zoom lens capable of image stabilization comprising: in order from an object side of the zoom lens:
a first lens group having a positive refractive power, the first lens group being fixed when the zoom lens varies a magnification thereof;
a second lens group having a negative refractive power and being capable of varying a magnification of the zoom lens;
a stop;
a third lens group having a positive refractive power, the third lens group being fixed when the zoom lens varies a magnification thereof; and
a fourth lens group having a positive refractive power, being capable of correcting an image plane variation when the zoom lens varies a magnification thereof, and being capable of focusing the zoom lens,
wherein the third lens group includes a 3a-th lens group having a positive refractive power, a 3b-th lens group having a negative refractive power, and a 3c-th lens group having a positive refractive power in this order from the object side,
the 3b-th lens group is adapted to be movable in a direction approximately orthogonal to an optical axis thereof so as to correct blurring of a taken image which is caused by a vibration of the zoom lens, and
the zoom lens satisfies conditional expressions (1) and (2):
8 <f 3 /fw <26 (1)
0.55<|(φ3 a +φ3 c )/(2×φ3 b )|<0.95 (2)
wherein
fw represents a focal length of the zoom lens at a wide angle end,
f3 represents a focal length of the third lens group,
φ3a represents a refractive power of the 3a-th lens group, which is a reciprocal of a focal length of the 3a-th lens group,
φ3b represents a refractive power of the 3b-th lens group, which is reciprocal of a focal length of the 3b-th lens group, and
φ3c represents a refractive power of the 3c-th lens group, which is reciprocal of a focal length of the 3c-th lens group.
2. The zoom lens capable of image stabilization according to claim 1 , wherein the 3b-th lens group includes one single lens or one cemented lens and has at least one aspherical surface.
3. The zoom lens capable of image stabilization according to claim 2 , wherein at least one of the 3a-th lens group and the 3c-th lens group includes one plastic lens.
4. The zoom lens capable of image stabilization according to claim 3 , further satisfying conditional expression (7):
3 <Bfw/fw <5.5 (7)
wherein Bfw represents a back focus at a wide angle end when removing an optical member having no refractive power between an imaging plane and a surface of a lens closest to the imaging plane.
5. The zoom lens capable of image stabilization according to claim 2 , further satisfying conditional expression (7):
3 <Bfw/fw <5.5 (7)
wherein Bfw represents a back focus at a wide angle end when removing an optical member having no refractive power between an imaging plane and a surface of a lens closest to the imaging plane.
6. The zoom lens capable of image stabilization according to claim 2 , wherein when the 3b-th lens group includes the one single lens, the one single lens is a negative lens having a concave surface directed to the object side and the one single lens satisfies conditional expressions (3) and (4):
ν 3b >35 (3)
n 3b >1.75 (4)
wherein
ν 3b represents an Abbe number of a material of the one single lens at the d-line, and
n 3b represents a refractive index of the material of the one single lens at the d-line.
7. The zoom lens capable of image stabilization according to claim 6 , wherein at least one of the 3a-th lens group and the 3c-th lens group includes one plastic lens.
8. The zoom lens capable of image stabilization according to claim 7 , further satisfying conditional expression (7):
3 <Bfw/fw <5.5 (7)
wherein Bfw represents a back focus at a wide angle end when removing an optical member having no refractive power between an imaging plane and a surface of a lens closest to the imaging plane.
9. The zoom lens capable of image stabilization according to claim 6 , further satisfying conditional expression (7):
3 <Bfw/fw <5.5 (7)
wherein Bfw represents a back focus at a wide angle end when removing an optical member having no refractive power between an imaging plane and a surface of a lens closest to the imaging plane.
10. The zoom lens capable of image stabilization according to claim 2 , wherein when the 3b-th lens group includes the one cemented lens of a positive lens and a negative lens, a most object-side surface of the cemented lens has a concave surface directed to the object side and the one cemented lens satisfies conditional expressions (5) and (6):
10<ν 3bN −ν 3bP <25 (5)
( n 3bN +n 3bP )/2>1.7 (6)
wherein
ν 3bP represents an Abbe number of a material of the positive lens at the d-line
ν 3bN represents an Abbe number of a material of the negative lens at the d-line,
n 3bP represents a refractive index of the material of the positive lens at the d-line, and
n 3bN represents a refractive index of the material of the negative lens at the d-line.
11. The zoom lens capable of image stabilization according to claim 10 , wherein at least one of the 3a-th lens group and the 3c-th lens group includes one plastic lens.
12. The zoom lens capable of image stabilization according to claim 11 , further satisfying conditional expression (7):
3 <Bfw/fw <5.5 (7)
wherein Bfw represents a back focus at a wide angle end when removing an optical member having no refractive power between an imaging plane and a surface of a lens closest to the imaging plane.
13. The zoom lens capable of image stabilization according to claim 10 , further satisfying conditional expression (7):
3 <Bfw/fw <5.5 (7)
wherein Bfw represents a back focus at a wide angle end when removing an optical member having no refractive power between an imaging plane and a surface of a lens closest to the imaging plane.
14. The zoom lens capable of image stabilization according to claim 1 , wherein at least one of the 3a-th lens group and the 3c-th lens group includes one plastic lens.
15. The zoom lens capable of image stabilization according to claim 14 , further satisfying conditional expression (7):
3 <Bfw/fw <5.5 (7)
wherein Bfw represents a back focus at a wide angle end when removing an optical member having no refractive power between an imaging plane and a surface of a lens closest to the imaging plane.
16. The zoom lens capable of image stabilization according to claim 1 , further satisfying conditional expression (7):
3 <Bfw/fw <5.5 (7)
wherein Bfw represents a back focus at a wide angle end when removing an optical member having no refractive power between an imaging plane and a surface of a lens closest to the imaging plane.
17. An imaging apparatus comprising a zoom lens capable of image stabilization according to claim 1 .