Photography – Having variable focal length of camera objective
Reexamination Certificate
2002-06-12
2003-08-19
Perkey, W. B. (Department: 2851)
Photography
Having variable focal length of camera objective
C359S692000
Reexamination Certificate
active
06608970
ABSTRACT:
BACKGROUND OF THE INVENTION
1) Field of the Invention
The present invention relates to a zoom optical system used for a photographing camera, specifically, for a lens-shutter camera, and to a camera using the same zoom optical system.
2) Description of Related Art
In recent years, lens-shutter cameras provided with a zoom lens have become popular, and requirement for a camera provided with a small-sized photographing lens with highly variable magnification have been raised. Regarding a zoom lens having a variable magnification ratio (ratio of the focal length of the entire system in the telephoto end position to the focal length of the entire system in the wide-angle end position) of 2 or 3, those with a two-unit zoom configuration arranging, in order from the object side, a positive refracting power and a negative refracting power are popularly used. Also, regarding a zoom lens having a variable magnification ratio of 3 or 4.5, those with a three-unit zoom configuration arranging, in order from the object side, a positive refracting power, a positive refracting power and a negative refracting power are popularly used.
A zoom lens with three-unit configuration allows fluctuation of aberrations to be small during zooming between the wide-angle end and the telephoto end. However, the configuration obliges the lens to be larger in size and more complex than a lens with two-unit zoom configuration, with larger number of lens elements and larger size of each lens unit. These features consequently raise the cost.
On the other hand, a zoom lens with two-unit configuration can be constructed of a smaller number of lens elements, to have a more simple structure. Therefore, it facilitates reduction in size and weight of a camera in which it is incorporated, and thus is advantageous in view of cost. For this reason, two-unit zoom configuration is often employed for a zoom lens of a compact camera.
However, the conventional zoom lens with two-unit configuration has a problem in that its small size and highly variable magnification cause large aberrations.
Conventional art to solve this problem is disclosed in Japanese Patent Application Preliminary Publication (KOKAI) No. Hei 11-258503, Japanese Patent Application Preliminary Publication (KOKAI) No. Hei 10-48523, Japanese Patent Application Preliminary Publication No. Hei 8-110468, etc. However, each of JP KOKAI No. Hei 11-258503 and JP KOKAI NO. Hei 8-110468 discloses a system having a variable magnification ratio greater than 3.3, with a telephoto ratio (ratio of the entire length of the entire system in the telephoto end position to the focal length of the entire system in the telephoto end position) greater than 0.9. Regarding the system recited in JP KOKAI NO. 10-48523 also, while the variable magnification ratio is 3, the telephoto ratio is as small as 0.9, which is not small enough to achieve compact sizing. Thus, these conventional systems are not preferable in view of cost or size. Also, such a system requires the lens frame to bear too large load. In addition, since such a zoom lens largely protrudes from the camera body, the center of gravity resides on the front portion of the camera. Accordingly, camera shake via user's hands often occurs.
SUMMARY OF THE INVENTION
In consideration of the problems stated above, an object of the present invention is to provide a compact zoom optical system of two-unit configuration that achieves good imaging performance, with a variable magnification ratio greater than 3 and a telephoto ratio smaller than 0.85, and a camera using the same zoom optical system.
Therefore, in order to achieve the above-mentioned object, a zoom optical system according to the first aspect of the present invention includes a lens system that consists of, in order from the object side, a first lens unit having a positive refracting power and a second lens unit having a negative refracting power. In variable magnification change from the wide-angle end through the telephoto end, each lens unit is moved toward the object side in such a manner that a space between the first lens unit and the second lens unit decreases. The first lens, unit consists of, in order from the object side, a first lens component having a positive refracting power, a second lens component having a negative refracting power, and a third lens component having a positive refracting power, which consists of one cemented-lens component. In addition, the following condition (1) is satisfied:
f
T
/f
W
>3 (1)
where f
T
is a focal length of the entire system in the telephoto end position, and f
W
is a focal length of the entire system in the wide-angle end position.
Also, a zoom optical system according to the second aspect of the present invention includes a lens system that consists of, in order from the object side, a first lens unit having a positive refracting power and a second lens unit having a negative refracting power. In variable magnification change from the wide-angle end through the telephoto end, each lens unit is moved toward the object side in such a manner that a space between the first lens unit and the second lens unit decreases. The first lens unit consists of, in order from the object side, a first lens component having a positive refracting power, a second lens component having a negative refracting power, and a third lens component having a positive refracting power, which consists of one cemented-lens component. The second lens unit includes at least one positive lens element and two negative lens elements. One of these two negative lens elements is a negative meniscus lens that is disposed on the most image side with a convex surface thereof being directed toward the image side. In addition, the following conditions (2) and (3) are satisfied:
L
T
/f
T
<0.85 (2)
1.67
<N
L23
(3)
where L
T
is a total length of the entire system in the telephoto end position, f
T
is a focal length of the entire system in the telephoto end position, and N
L23
is a refractive index of the negative lens element disposed on the most image side in the second lens unit.
Also, in each of the first and second aspects, it is preferred that the following condition (4) is further satisfied:
1.7
<N
L23
(4)
where N
L23
is a refractive index of a negative lens element that is disposed on the most image side in the second lens unit.
Also, in each of the first and second aspects, it is preferred that the following conditions (5) and (6) are further satisfied:
3.8
<f
T
/f
1
<5.5 (5)
−7.0
<f
T
/f
2
<−5.0 (6)
where f
1
is a focal length of the first lens unit, and f
2
is a focal length of the second lens unit.
Also, in each of the first and second aspects, it is preferred that the following condition (7) is further satisfied:
0.02
<D
12
/f
W
<0.06 (7)
where D
12
is a space between the first lens component and the second lens component, and f
W
is a focal length of the entire system in the wide-angle end position.
Also, in each of the first and second aspects, it is preferred that the second lens unit includes a plastic lens element having at least one aspherical surface.
Also, in each of the first and second aspects, it is preferred that the following condition (8) is further satisfied:
0.03
<D
12
/f
W
<0.05 (8)
where D
12
is a space between the first lens component and the second lens component, and f
W
is a focal length of the entire system in the wide-angle end position.
Also, in each of the first and second aspects, it is preferred that the following condition (9) is satisfied:
N
1N
>1.8 (9)
where N
1N
is a refractive index of any negative lens element in the first lens unit.
Also, in each of the first and second aspects, it is preferred that the following condition (10) is satisfied:
0.05
<D
12
/h
<0.1 (10)
where D
12
is a space between the first lens component and the second lens component, and h is a maximum image height on the image surface.
Also, in the first aspect, it is
Olympus Optical Co,. Ltd.
Perkey W. B.
Pillsbury & Winthrop LLP
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