Optical: systems and elements – Lens – With light limiting or controlling means
Reexamination Certificate
2000-02-16
2001-04-24
Sugarman, Scott J. (Department: 2873)
Optical: systems and elements
Lens
With light limiting or controlling means
C359S699000
Reexamination Certificate
active
06222684
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a maximum-aperture regulating apparatus in which a maximum aperture size of a shutter blade is changed in accordance with a focal length of a taking lens.
2. Description of the Related Art
It is known that a low-priced shutter mechanism (program shutter) which is also used as a diaphragm employs a motor of a moving-magnet type. As to this motor, a rotor of a permanent magnet is reciprocated within a range of a predetermined angle in response to a current direction flowing in a coil. Upon this, a shutter blade is opened and closed. Although the motor of the moving-magnet type is inexpensive in comparison with a pulse motor, it is impossible to accurately control an aperture size of the shutter blade in accordance with an exposure value. For this, a regulating device is provided for regulating a rotational range of the shutter blade to a diameter at which the whole of a shutter opening is bared. An exposure amount is controlled by managing an operation time of the shutter blade.
There is a system in which an operation time of a shutter blade is controlled in accordance with an exposure value. In this system, when a taking lens is a zoom lens for example, brightness of the taking lens changes at a wide-angle side and at a telephoto side. Thus, it is necessary to make an aperture size of the shutter blade smaller at the wide-angle side in comparison with the telephoto side. Moreover, it is desirable to make a stop smaller at the wide-angle side in order to reduce a image periphery blur caused by spherical aberration of the lens. In view of this, Japanese Patent Laid-Open Publication No. 3-107132 proposes a regulating device for a zoom lens stop in which a maximum aperture size of a shutter blade, which is also used as a diaphragm, is changed in accordance with a focal length of a taking lens.
Regarding the device described in the above-mentioned Publication, a program shutter which is used as a diaphragm is incorporated in a lens group moving inside a lens barrel along an optical axis direction. From this program shutter, a part of a drive lever for driving the shutter blade projects toward an outer periphery. When zooming is performed within a prescribed range of the wide-angle side, the part of the drive lever engages with a cam to regulate a rotational range of the drive lever. The cam is provided on an inner surface of the lens barrel so as to incline in the optical axis direction. In this way, the maximum aperture size of the shutter blade is regulated in accordance with the focal length of the taking lens within the prescribed range.
However, in the device described in the above-mentioned Publication, the cam inclining in the optical axis direction is provided on the inner surface of the lens barrel so that the cam requires a length corresponding to a moving amount of the lens group. This lens group moves in the optical axis direction within the prescribed range of the wide-angle side. In case the moving amount of the lens group is long, the cam becomes long as well. Thus, there arises a problem in that the lens barrel has a large size in itself. Contrary, in case the moving amount of the lens group is small, it is necessary to steeply incline the cam. In this case, it is difficult to accurately regulate the maximum aperture size of the shutter blade.
SUMMARY OF THE INVENTION
In view of the foregoing, it is a primary object of the present invention to provide an aperture regulating device in which a size of a lens barrel itself is reduced.
It is a second object of the present invention to provide an aperture regulating device in which a maximum aperture size of a shutter blade can be accurately regulated in accordance with a focal length of a taking lens.
In order to achieve the above and other objects, the aperture regulating device according to the present invention comprises a shutter block which is provided with an aperture regulating member for regulating a maximum aperture size.
The shutter block includes two shutter blades rotated for forming an aperture. One of the shutter blades abuts on the aperture regulating member so as to regulate the maximum aperture size. In the present invention, the maximum aperture size is altered by changing an abutting position of the shutter blade and the aperture regulating member.
Changing the abutting position is performed by working of a projection and a cam groove. The projection is integrally formed with the aperture regulating member, and the cam groove is formed in an inner face of a cam barrel so as to engage with the projection. The cam barrel is rotated to move in an optical axis direction, and the cam groove is obliquely formed in a rotational direction of the cam barrel.
The cam groove slopes in the rotational direction of the cam barrel. In other words, depth of the cam groove changes along the rotational direction of the cam barrel. Thus, the projection engages with the cam groove more deeply as the cam barrel is rotated. In accordance with an engagement amount of the projection and the cam groove, the abutting position of the shutter blade and the aperture regulating member is changed. Upon the change of the abutting position, the maximum aperture size defined by the shutter blades are altered.
In this way, the maximum aperture size is regulated by the workings of the projection of the aperture regulating member and the cam groove formed in the inner face of the cam barrel. Incidentally, the maximum aperture size is regulated in accordance with a focal length of a taking lens in order to prevent a image periphery blur from occurring.
REFERENCES:
patent: 3-107132 (1991-05-01), None
Fuji Photo Optical Co., Ltd.
Sugarman Scott J.
Young & Thompson
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