Zoom lens and imaging apparatus
A zoom lens includes a first lens group having positive refracting power, a second lens group having negative refracting power, a third lens group having positive refracting power, a fourth lens group having negative refracting power and a fifth lens group having negative refracting power in order from an object side, in which the lens groups move in magnification change from a wide angle end to a telephoto end such that a gap between the first lens group and the second lens group increases and a gap between the second lens group and the third lens group decreases, a negative lens group disposed closer to an image focusing side than a diaphragm among all lens groups is set as a focusing lens group, and the focusing lens group moves toward the image focusing side at focusing from infinity to a close object, the zoom lens satisfies a conditional expression.
1. A zoom lens including a first lens group having positive refracting power, a second lens group having negative refracting power, a third lens group having positive refracting power, a fourth lens group having negative refracting power and a fifth lens group having negative refracting power in order from an object side;
wherein a surface of the fifth lens group disposed closest to the object side is concave;
wherein the lens groups move in magnification change from a wide angle end to a telephoto end such that a gap between the first lens group and the second lens group increases and a gap between the second lens group and the third lens group decreases;
a negative lens group disposed closer to an image plane side than a diaphragm among all lens groups is set as a focusing lens group, and the focusing lens group moves toward the image plane side in focusing from infinity to a close object;
the zoom lens satisfies conditional expression (1); and the focus lens group is composed of a single lens block of a meniscus shape having a concave surface at image plane side, and satisfies conditional expression (2) below:
[Expression 1]
0.45≦β5 T/β 4 T≦ 1.900 (1)
where
β4T: Lateral magnification in telephoto end of fourth lens group
β5T: Lateral magnification in telephoto end of fifth lens group
[Expression 2]
3.10≦ ra 4/ rb 4≦210.00 (2)
where
ra4: Curvature radius of object side surface of focus lens group
rb4: Curvature radius of image plane side surface of focus lens group.
2. The zoom lens according to claim 1 , wherein the zoom lens satisfies conditional expression (3) below:
[Expression 3]
1.00 f 1/( fw×ft ) 1/2 ≦3.00 (3)
where
f1: Focal length of first lens group,
fw: Focal length of the zoom lens at the wide angle end
ft: Focal length of the zoom lens at the telephoto end.
3. The zoom lens according to claim 1 , wherein the zoom lens satisfies conditional expression (4) below:
[Expression 4]
1.30≦β4 W×β 5 W≦ 3.60 (4)
where
β4W: Lateral magnification in wide angle end of fourth lens group,
β5W: Lateral magnification in wide angle end of fifth lens group.
4. The zoom lens according to claim 1 ,
wherein the third lens group includes at least a vibration-compensation lens group composed of a single lens block;
hand-shake compensation is performed by moving the vibration-compensation lens group in a direction perpendicular to an optical axis; and satisfies conditional expression (5) below:
[Expression 5]
−1.30≦ ra 3/ rb 3≦−0.10 (5)
where
ra3: Curvature radius at object side surface of vibration-compensation lens group,
rb3: Curvature radius at image focusing side surface of vibration-compensation lens group.
5. The zoom lens according to claim 1 ,
wherein the fifth lens group is at least composed of a single lens block of a meniscus shape having a concave surface at object side; and
the single lens block of the meniscus shape has a negative focal length and satisfies conditional expression (6) below:
[Expression 6]
0.00< ra 5/ rb 5≦3.00 (6)
where
ra5: Curvature radius of object side surface of single lens block of meniscus shape
rb5: Curvature radius of image plane side surface of single lens block of meniscus shape.
6. An imaging apparatus including the zoom lens according to claim 1 , and an imaging sensor that converts an optical image formed on an image plane side by the zoom lens into an electrical signal.