1. Field of the Invention
The present invention relates to a rotary shutter device for use in an electronic still camera or a VTR camera in which the optical image of an object focused on an XY-addressable solid-state imaging device such as a MOS image sensor or a CCD image sensor is photoelectrically converted into a video signal that is delivered to a recorder or other device, and more particularly to a rotary shutter device having adjusting blades for adjusting the angular widths or intervals of the openings in a shutter blade through which the imaging device can be exposed to incident light, thereby adjusting the shutter speed.
2. Description of the Prior Art
There are known electronic photographic cameras, particularly of a portable type, with a solid-state imaging device such as a MOS image sensor or a CCD image sensor. The know electronic photographic cameras have a rotary shutter disposed between the objective lens and the image sensor for achieving higher and more uniform shutter speeds.
The rotary shutter is composed of a shutter disc or blade having openings defined therein and mounted on the rotating shaft of a step motor or the like. When the step motor is energized, the shutter disc is rotated to uncover and cover the openings for transmitting and shutting off light falling on the imaging device. The rotary shutter can operate at high and uniform speeds and is highly durable in operation.
In view of the above advantages of the rotary shutter, it has been proposed to employ the rotary shutter as the shutter in a camera for recording successive images, such as a VTR camera. The solid-state imaging device is exposed to each object image through the openings of the rotary shutter in either 1/60 second (sequential scanning) or 1/30 second (interlaced scanning), depending on the TV broadcasting system in use. The shutter blade therefore rotates at a constant speed. This system is however disadvantageous in that a desired exposure time cannot be selected by changing the speed of rotation of the shutter disc. For changing the exposure time as desired in the camera for recording successive images, it is preferable to vary the angular intervals of the openings of the rotary shutter. One example of such a rotary shutter is composed of two superimposed shutter blades having sectorial shapes and movable relatively to each other for adjusting the opening angle therebetween. The camera with this rotary shutter has a shutter speed selecting mechanism for allowing the user to select the exposure time or shutter speed.
Since the solid-state imaging device is scanned while being shielded from light, the rotary shutter is required to have light-shielding portions aside from the openings. For setting the shutter speed to 1/60 second, because the time required for scanning the imaging device for one field is normally 1/60 second, the opening angles of the openings should be selected so as to make the openings larger than the photodetector surface of the imaging device, and the rotary shutter should be stopped against rotation to bring one of the openings in alignment with the imaging device.
If the rotary shutter were to be stopped by depressing a rotary shutter stop button, the user would be required both to operate the shutter speed selecting mechanism for a desired shutter speed setting and to depress the rotary shutter stop button. The required operation would be so complex and time-consuming that the user would tend to miss good chances for taking pictures.
There is a recent demand for a function that makes it possible to select one of the recorded moving images and produce it as a still image. To meet this demand, many VTR systems commercially available today include a mechanism for producing still images.
Where the image of an object, particularly a moving object, is produced as a still image by the successive-image recording camera with the rotary shutter, and the still image is produced by an exposure through more than one opening in the shutter blades, the resulting image is blurred as it suffers irregularities between adjacent horizontal scanning lines.