A zoom lens is provided and has: a first lens of a negative lens; a second lens of a positive lens; an aperture stop; a third lens of a negative lens; and a fourth lens of a positive lens in this order from an object side of the zoom lens. A zooming operation of the zoom lens is performed by varying mutual distances among the first to fourth lenses, and the zoom lens satisfies specific conditional expressions.
1. A zoom lens comprising: a first lens of a negative lens; a second lens of a positive lens; an aperture stop; a third lens of a negative lens; and a fourth lens of a positive lens in this order from an object side of the zoom lens,
wherein a zooming operation of the zoom lens is performed by varying mutual distances among the first to fourth lenses, and
the zoom lens satisfies conditional expressions (1) to (4):
0.35< f 2/ f 4<0.70 (1)
0.04<( dt−dw )/ fw< 0.40 (2)
1.65< f 4/ fw< 2.20 (3)
50<νd1 (4)
wherein
f 2 designates a focal length of the second lens;
f 4 designates a focal length of the fourth lens;
dt designates a distance along an optical axis between the second lens and the third lens in a wide-angle end of the zoom lens;
dw designates a distance along the optical axis between the second lens and the third lens in a telephoto end of the zoom lens;
fw designates a focal length of a total system of the zoom lens in the telephoto end; and
νd 1 designates an Abbe number of the first lens at the d-line.
2. The zoom lens according to claim 1 , wherein the zooming operation is performed by moving at least the second lens and the third lens along the optical axis.
3. The zoom lens according to claim 1 , wherein a distance between the fourth lens and an imaging plane is kept constant at least in the zooming operation.
4. The zoom lens according to claim 1 , wherein the zooming operation is performed by moving the first lens and the fourth lens jointly along the optical axis.
5. The zoom lens according to claim 1 , wherein a distance between the first lens and an imaging plane is kept constant.
6. The zoom lens according to claim 1 , wherein a focusing operation of the zoom lens is performed by moving the third lens along the optical axis.
7. The zoom lens according to claim 1 , wherein at least the first lens and the second lens each are made of an organic material.
8. The zoom lens according to claim 1 , further comprising:
a temperature sensing portion that measures an environmental temperature;
a control portion that calculates a correction value of a focal point of the zoom lens based on the environmental temperature and outputs a control signal on the correction value of the focal point; and
a driving portion that makes at least one of the first to fourth lenses move by a distance corresponding to the correction value of the zoom lens in response to the control signal.
9. The zoom lens according to claim 1 , wherein the zoom operation and the focusing operation are performed alternately by continuously moving at least the third lens along the optical axis.
10. A zoom lens according to claim 1 , wherein a reflection surface forming a bending optical system is provided in or near the first lens.