Photography – Having variable focal length of camera objective
Reexamination Certificate
2002-10-30
2004-04-06
Perkey, W. B. (Department: 2851)
Photography
Having variable focal length of camera objective
C348S240300, C359S714000, C359S764000, C359S684000
Reexamination Certificate
active
06718132
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a compact zoom lens suitable for use in video cameras and still video cameras, a camera apparatus using the zoom lens, and a portable information terminal apparatus.
2. Discussion of the Background
In a zoom lens for use in video cameras and still video cameras, recently, as demands for a higher zooming ratio, a wider field angle and a higher resolution increase, and at the same time for meeting demands for a smaller size, a lighter weight and a reduced cost, reducing the overall length and the outer diameter of the zoom lens and decreasing the number of pieces of lens composing the zoom lens are becoming imperative.
As a zoom lens for meeting the above-described demands, a type of zoom lens has been proposed, in which, in order from the object side, a first lens group having a positive refracting power, a second lens group having a negative refracting power, a third lens group having a positive refracting power, a fourth lens group having a positive refracting power, and a fifth lens group having a positive refracting power are arranged. By moving the second lens group toward the imaging plane side, zooming of the zoom lens from the short focal length end to the long focal length end is performed, and a shift in the position of an imaging plane of the zoom lens due to the movement of the second lens group for the zooming is corrected by the fourth lens group. Japanese Patent Laid-open Publication No. 6-180424, Japanese Patent Publication No. 3109342, and Japanese Patent Laid-open Publication No. 9-90221 describe examples of zoom lenses of such type. In each of the zoom lenses of these examples, a shift in the position of an imaging plane occurring in connection with zooming is corrected by movement of the fourth lens group.
Each of the zoom lenses having five lens groups described in the above publications, respectively, is configured such that the fourth lens group is moved solely for correcting a shift in the position of an imaging plane occurring in connection with zooming, and the movement of the fourth lens group does not contribute to the zooming at all. The function of zooming is mostly performed by the second lens group. For this reason, the moving amount of the second lens group for zooming is large, and as a result, the first lens group must be arranged at a distant position from an aperture diaphragm arranged in the third lens group. This leads to increasing the size of the first lens group and furthermore to increasing the overall size of the zoom lens.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above-discussed and other problems and addresses the above-discussed and other problems.
Preferred embodiments of the present invention provide a novel zoom lens that has a high zooming ratio exceeding 4.5 times while being extremely small in the outer diameter and the overall length thereof and a wide field angle with a half field angle at the short focal length end of 30° or more, and that can attain a high resolution. The preferred embodiments also provide a camera apparatus using the zoom lens, and a portable information terminal apparatus using the camera apparatus.
According to a preferred embodiment of the present invention, a zoom lens includes a first lens group having a positive refracting power, a second lens group having a negative refracting power, a third lens group having a positive refracting power, a fourth lens group having a positive refracting power, and a fifth lens group having a positive refracting power. The first lens group, the second group lens, the third lens group, the fourth lens group, and the fifth lens group are arranged in succession. The zoom lens is configured such that, when zooming from a short focal length end toward a long focal length end, the second lens group lens moves toward the third lens group and the fourth lens group moves toward a side of the third lens group, and the fifth lens group corrects the zooming and a shift in a position of an imaging plane of the zoom lens caused by movement of the second lens group and the fourth lens group. When a distance from a first lens surface of the zoom lens at the long focal length end to the imaging plane is &Sgr;d, a synthesized focal length of the first lens group through the fifth lens group is fw, and a synthesized focal length of the first lens group through the fifth lens group is ft, a following conditional formula is satisfied:
1.45
<&Sgr;d
/(
ft−fw
)<2.2.
Thus, the above-described zoom lens is configured such that when zooming, the fourth lens group is also moved to perform a portion of the zooming and a shift in the position of the imaging plane of the zoom lane involved in the zooming is corrected by moving the fifth lens group. Thereby, the moving amount of the second lens group can be suppressed small, so that the distance of the first lens group from an aperture diaphragm can be reduced and the outer diameter of the first lens group can be made relatively small, and at the same time, the overall size of the zoom lens can be made relatively small. Further, freedom in enhancing the performance of the zoom lens is increased by moving the fifth lens group, so that enhancement of the performance of the zoom lens can be achieved.
The above conditional formula specifies an overall size of the zoom lens, and if the upper limit is exceeded, the overall length of the zoom lens will increase, the outer diameter of the first lens group will increase, the cost of the zoom lens will increase, and the size of a camera using the zoom lens will increase. If the lower limit is exceeded, the power of each lens group will be too strong, so that satisfactory imaging performance will not be obtained. For achieving a higher performance of the zoom lens, it is preferable that the zoom lens is configured such that the following conditional formula is satisfied:
1.6
<&Sgr;d
(
ft−fw
)<2.2.
In the above-described zoom lens, the first lens group may be mounted at a fixed position. That is, the first lens group may be a fixed lens group that does not move when the zoom lens is zoomed and when a portion of lens groups moves for focusing. For realizing moving of moving lens groups of a zoom lens with a simple mechanism, it is preferable that the zoom lens is configured such that the first lens group is fixed. The first lens group has a largest outer diameter among the lens groups constituting the zoom lens, and consequently, the first lens group is relatively heavy. Accordingly, it is hard to realize moving of the first lens group with a simple mechanism and reduced power consumption. Further, if the zoom lens is configured such that focusing is performed by the first lens group, the peripheral light quantity at a short photographing distance is greatly reduced as a result of movement of the first lens group, which is undesirable. For avoiding this disadvantage, the first lens group must be made extremely large. By configuring the zoom lens such that the first lens group is fixed as above, as might be expected, the distance from the first lens surface of the zoom lens to the imaging plane is constant through the entire zooming range.
In the above-described zoom lens, an aperture diaphragm may be arranged in the vicinity of the third lens group, and in particular, it is preferable that the aperture diaphragm is arranged at a most outside position of the third lens group at the side of the second lens group. Further, the third lens group including the aperture diaphragm may be mounted at a fixed position.
Generally, a shutter is provided at the position of the aperture diaphragm. A mechanism for moving the shutter is relatively complicated. Further, if the shutter is configured to be moved, vibration at the time of driving the shutter tends to be transmitted to other parts of the zoom lens. This causes deterioration of the performance of the zoom lens, e.g. image burring. Thus, it is preferable that the third lens group including a shutter is not moved.
In the ab
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Perkey W. B.
Ricoh & Company, Ltd.
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