Photography – Camera detail – Shutter
Reexamination Certificate
1999-07-14
2001-07-31
Mahoney, Christopher E. (Department: 2851)
Photography
Camera detail
Shutter
C396S463000, C396S478000
Reexamination Certificate
active
06269226
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a shutter device for a camera and more particularly to a motor-driven shutter.
2. Description of the Related Art
Programmed shutters of the kind having sectors which form a lens aperture, a stepping motor which rotates stepwise forward or backward according to the phase sequence of driving pulses time-serially supplied, a transmission gear train which transmits the rotation of the stepping motor to the sectors and an arrangement for controlling the opening and closing of the sectors through the rotation of the stepping motor, have been known from, for example, Japanese Utility Model Publication No. HEI 4-47697, Japanese Patent Application Laid-Open No. HEI 3-184029, Japanese Utility Model Laid-Open No. SHO 62-89624, Japanese Patent Application Laid-Open No. SHO 57-150829 (corresponding to U.S. Pat. No. 4,325,614), etc.
Generally, however, the stepping motors such as the motors employed in the prior art examples mentioned above do not permit to increase their rotation speed at the start of driving and at the time of change-over from forward rotation to backward rotation. The speed of the sectors thus cannot be increased at such a time. This shortcoming of the stepping motor has necessitated use of only a half-open area of the aperture when it is necessary to obtain a high shutter speed for a high luminance field.
A shutter permitting use of only the half-open area for a high luminance field presents problems in that the intrinsic power of a photo-taking lens cannot be fully used and that, in the event of fill-in flash photography, the exposure interlocking (synchronizing) distance of the flash device becomes nearer.
To solve these problems, it has been contrived to arrange a shutter device to include a first shutter which is normally closed and a second shutter which is normally open, to open the first shutter and close the second shutter by energizing them in such a way as to cause the second shutter to cover an aperture formed by the first shutter and to obtain a required amount of exposure by electrically controlling the points of time at which the first and second shutters respectively begin to operate.
However, in order to obtain a high shutter speed even for the full open area of the aperture, the shutter device of this kind necessitates increasing also the shutter operating speed. Unevenness in length of time required before the actual start of operation of the first and second shutters after receipt of an operation start signal results in an error in the amount of exposure. Particularly, since the conventional shutter device uses an electromagnetic device as a drive source for driving the shutters, the unevenness in operation start time is great and further increases accordingly as the shutter speed increases to give a greater error in amount of exposure for a high shutter speed.
SUMMARY OF THE INVENTION
This invention is directed to the solution of the above-stated problems of the prior art. Therefore, it is one aspect of this invention that a shutter device or a camera having the shutter device is arranged according to this invention to be capable of operating at a high shutter speed. The shutter device according to this invention includes a first light blocking member movable for varying an amount of opening, a first motor arranged to drive the first light blocking member, a second light blocking member movable for varying an amount of opening, a second motor arranged to drive the second light blocking member, and control means for controlling the first motor and the second motor. The first and second light blocking members are thus arranged to be driven by the respective independent motors, so that the shutter device can be operated at a high speed by these motors.
Another aspect of this invention lies in that a shutter device according to this invention has a plurality of light blocking members movable for varying an amount of opening and driving means for driving the plurality of light blocking means, wherein the plurality of light blocking members have an area in which to be driven by the driving means without changing a relative position between the plurality of light blocking members, so that the shutter device can be stably operated.
These and other aspects and features of this invention will become apparent from the following detailed description of embodiments thereof taken in connection with the accompanying drawings.
REFERENCES:
patent: 2283533 (1942-05-01), Brueske
patent: 2322733 (1943-06-01), Steiner
patent: 4005448 (1977-01-01), Iwata et al.
patent: 5164766 (1992-11-01), Morita
patent: 5953550 (1999-09-01), Aoshima
Canon Kabushiki Kaisha
Mahoney Christopher E.
Robin Blecker & Daley
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