Zoom lens with vibration reduction function

Details Zoom lens with vibration reduction function Zoom lens with vibration reduction function

1994-11-28

2001-11-20

Nguyen, Thong (Department: 2872)

Optical: systems and elements

Image stabilization

By movable refractive structure

C359S554000, C359S686000

Reexamination Certificate

active

06320698

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a zoom lens with a vibration reduction function and, more particularly, to a vibration reduction method for zoom lenses for a still camera, video camera, and the like.
2. Related Background Art
A conventional zoom lens with a vibration reduction function corrects a variation in image position caused by, e.g., a camera shake by moving an arbitrary lens group in the zoom lens constituted by two or more lens groups in a direction substantially perpendicular to the optical axis, as described in Japanese Laid-Open Patent Application Nos. 1-189621 and 1-191113. Also, another zoom lens with a vibration reduction function corrects a variation in image position caused by, e.g., a camera shake by moving a partial lens group in a fixed first lens group upon zooming in a direction substantially perpendicular to the optical axis, as described in Japanese Laid-Open Patent Application No. 1-284823.
Note that correcting a variation in image position caused by, e.g., a camera shake by moving the lens group in a direction substantially perpendicular to the optical axis will be referred to as “vibration reduction” in this specification.
However, the above-mentioned prior arts are not suitable for a lens for a still camera or a video camera since a sufficient back focus cannot be assured and a large zoom ratio cannot be realized for a lens for a single-lens reflex camera or a lens for a video camera.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of the above situation and has as an object to provide a high-performance zoom lens for a still camera or a video camera, which provides high performance especially from a normal range to a wide-angle range.
In order to achieve the above object, according to the present invention, a zoom lens, which comprises, in the following order from the object side, a first lens group G
1
having a negative refracting power, a second lens group G
2
having a positive refracting power, a third lens group G
3
having a negative refracting power, and a fourth lens group G
4
having a positive refracting power, and in which when zooming is effected from the wide-angle end to the telephoto end, the interval between the first and second lens groups G
1
and G
2
decreases, the interval between the second and third lens groups G
2
and G
3
increases, and the interval between the third and fourth lens groups G
3
and G
4
decreases, comprises displacement means for attaining vibration reduction by moving the third lens group G
3
or a partial lens group in the third lens group G
3
in a direction substantially perpendicular to the optical axis, and satisfies the following condition:
0.2<|
f
3
|/(
fW·fT
)
½
<5
where fW is the focal length of the entire lens system at the wide-angle end, fT is the focal length of the entire lens system at the telephoto end, and f
3
is the focal length of the third lens group G
3
.
According to a preferred aspect of the present invention, the zoom lens satisfies:
0.3<|
f
2
/f
1
|<3
where f
1
is the focal length of the first lens group G
1
, and f
2
is the focal length of the second lens group G
2
. A stationary flare stop for shielding unnecessary rays upon movement of the third lens group G
3
in the direction substantially perpendicular to the optical axis for vibration reduction is preferably arranged on the optical axis.
The zoom lens of the present invention adopts the following arrangement to be suitable for a zoom lens for a still camera or a video camera. That is, the zoom lens comprises, in the following order from the object side, the first lens group G
1
having a negative refracting power, the second lens group G
2
having a positive refracting power, the third lens group G
3
having a negative refracting power, and the fourth lens group G
4
having a positive refracting power, and when zooming is effected from the wide-angle end to the telephoto end, the interval between the first and second lens groups G
1
and G
2
decreases, the interval between the second and third lens groups G
2
and G
3
increases, and the interval between the third and fourth lens groups G
3
and G
4
decreases.
The characteristic features of the zoom lens with the above arrangement are that (i) the lens is suitable for achieving a lens having a wider angle, (ii) the lens is suitable for achieving a lens having a higher magnification, and (iii) the back focus can be easily assured.
With these excellent characteristics, the zoom lens with the above arrangement is widely used as zoom lenses for still cameras and video cameras.
The present invention provides optimal conditions for attaining vibration reduction while assuring good imaging performance for a zoom lens of this type.


REFERENCES:
patent: 3771853 (1973-11-01), Nakamura
patent: 4591235 (1986-05-01), Tokumaru et al.
patent: 4653873 (1987-03-01), Kawamura
patent: 4978205 (1990-12-01), Sato
patent: 5069537 (1991-12-01), Kitagishi
patent: 5182671 (1993-01-01), Kitagishi et al.
patent: 5249079 (1993-09-01), Umeda
patent: 1-189621 (1989-07-01), None
patent: 1-191113 (1989-08-01), None
patent: 1-284823 (1989-11-01), None

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