JPS5975769A - Image pickup device using focal plane shutter - Google Patents

Abstract

PURPOSE:To reduce the signal deterioration of a solid-state image pickup element due to a dark current by starting running a front curtain of a focal plane shutter before a vertical scan of the solid-state image pickup element is completed, and starting reading a signal out of the solid-state image pickup element before the run of a rear curtain is completed. CONSTITUTION:After a release switch signal 6 is generated, an sperture which is open so far starts stopping-down operation to a specific position synchronously with an initial synchronizing signal and a signal (c) is generated to hop up a mirror. Said operations are completed and then a start signal (e) for the front curtain is generated, so that the front curtain starts running. At this time, a sensor clock (d) is still supplied as mentioned above and unnecessary charges are discharged from a sensor 8. The scanning of the sensor 8 is stopped after the discharging is completed. A start signal (f) for the rear curtain is generated during said period and an electromagnet locking the rear curtain is operated to start the rear curtain. When exposure is completed, a signal is read out of the sensor in the following one field for recording.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an imaging device using a solid-state imaging device and a focal plane shutter.

Conventionally, 'MO8 type O8 element, CI D (Char
geInjection Device) 7. c.
In imaging devices that use a solid-state image sensor as an image sensor, which does not have its own shutter function, a mechanical shutter is used to control the exposure time, especially for single-lens reflex electronic still cameras that allow for interchangeable lenses. A focal plane shutter is suitable for this, and a V lens shutter is unsuitable due to its structure. From such a solid-state image sensor -
Figure 1 shows the temporal relationship between sensor operation and shutter timing in a conventional electronic still camera that combines an image sensor and focal plane shutter.
) (6). In Figure 1, the horizontal axis is time, the vertical axis is the position of the front and rear curtains of the shutter on the imaging surface (which can be thought of as the curtain surface of a focal plane shutter), and the electric vertical Directional scanning and the movement of the leading and trailing shutter curtains are shown together, with Figure 1 (cL) showing the shutter speed of 1/60 seconds, and Figure 1 (4') showing the shutter speed of 11,500 seconds. In conventional electronic still cameras, in order to simplify control, the synchronous signal generator, which controls the time of each part including the sensor, is operated constantly. It is common to control the sensor operation at the shutter timing in synchronization.

In FIG. 1 (aX8), the solid diagonal line drawn across the effective imaging surface width indicates the vertical position of the scanning line accessed by the vertical scanning of the cell, and the dashed diagonal line 2 shows that scanning should normally be performed in this manner in terms of timing, or that scanning is stopped for exposure.

With conventional electronic still camera shutter timing,
As shown in Figure 1 (cLXJ), first, prior to exposure, one vertical scan is performed to discharge unnecessary charges (dark current charges), and after this is completed, the front curtain of the focal plane shutter is released, and a predetermined After the exposure time (Fig. 1 (
6) is 1/60 second, and Figure 1 (4) is 1/500 second.
seconds later), the second curtain is released.

After the trailing curtain has completed running, vertical scanning is performed to read out the signal charge at the next synchronizing signal timing as shown in the figure, in synchronization with the synchronizing signal that is repeatedly operated at a constant cycle. However, when reading the signal charge after the trailing curtain has completed running, for example, when a rotating magnetic disc is used as the recording medium, there is a risk that the rotating servo of the magnetic recording system may be affected by mechanical vibrations of the camera body due to shutter operation. In this case, it is necessary to further delay the reading vertical scan by one cycle. The vertical scanning time of the sensor is 1/6o second (166 m5ec, ) for one field,
Moreover, the running time of the shirt curtain is 4 to 10 m5ec.

For example, when the shutter speed is 1/60 seconds as shown in Figure 1 (cL), charge accumulation is required for at least 6 to 4 times as long as 1/60 seconds to even obtain a field image. Therefore, the influence of the generation and accumulation of dark current charges during the period from unnecessary charge discharge to the start of exposure and from the completion of exposure to the start of signal charge readout cannot be ignored. In the case of obtaining an image for one frame, it is necessary to add 1/60 second to the accumulation time.
The same is true for the high-speed shutter (11,500 seconds) shown in the figure (ladle), and the required storage time is 1 for the field image.
/60 seconds, and the frame image is 6 to 4 times that of 1/60 seconds, and signal deterioration due to dark current cannot be ignored.

The present invention solves these drawbacks and provides an imaging device suitable for an electronic still camera using a focal plane shutter, which shortens the signal charge accumulation time to the necessary minimum and has little signal deterioration due to dark current of the solid-state imaging device. is intended to provide.

That is, in an apparatus of the present invention for achieving such an object, in an imaging device comprising seven combinations of a solid-state image sensor and a focal plane shutter, each of which reads signal charges by sequential scanning in the vertical direction, the solid-state image sensor before the vertical scanning of the solid-state image sensing device is completed, which is performed for the last unnecessary charge discharge prior to photographing exposure by aligning the vertical scanning direction of the focal plane shutter with the running direction of the leading and trailing curtains of the focal plane shutter. The front curtain of the focal plane shutter is started to run, and the signal readout from the solid-state image sensor is started before the focal plane shutter finishes running of the rear curtain. This eliminates extra time from the signal charge accumulation time to reduce signal deterioration due to dark current in the solid-state image sensor, and also allows mechanical vibration due to shutter operation to occur well in advance of signal readout and recording. .

To explain the present invention together with the illustrated embodiment, FIG. 2 is a block diagram showing the configuration of an electronic still camera as an application example of the imaging device of the present invention. In this example, a focal plane shutter and an image sensor are used to capture images. However, the obtained methyl image signal is FM-modulated and recorded on a magnetic sheet.

In Fig. 2, (1) in Fig. 1 is the photographing lens, and (2) is the aperture, and the action of the clutch (3) switches between automatic iris operation by the motor (4) and automatic aperture by the aperture mechanism (5). It has become.

When the auto iris is activated, the mirror (flipped up 6 points,
In addition, the focal plane shutter (7) is in a fully open state, and the image sensor (8) consisting of a solid-state image sensor is always irradiated with light. The image sensor (8) is constantly scanned according to the television system, and the video signal is finally displayed on the electronic viewfinder (9).
At this time, the optical finder 00 is not used.

A color temperature correction filter C11 is installed between the mirror (6) and the focal plane shutter (7) to compensate for differences in lighting conditions, and an optical low-pass filter (A) made of crystal is used to remove horizontal aliasing distortion. is provided.

A silicon photodiode α→ is provided as a photometric element at the bottom of the camera body to enable TTL photometry.

The curtain surface processing is performed so that the spectral reflectance of the curtain surface of the focal plane shutter (7) becomes equal to the spectral reflectance of the light receiving surface of the image sensor (8). 0→ is a photometry circuit, which transmits photometry information to the camera timing control circuit α→,
It is used to generate a shutter trailing curtain start signal etc. during exposure.

The mirror part mechanism (IQ and mirror drive mechanism α7 that drives the four-plane shutter (7)) related to the vertical movement of the mirror (6), and the shutter drive Isokaharu are both driven by a common motor. It is now charged,
The motor α field is controlled by a shutter drive circuit.

CD is an aperture control circuit.

In addition, an autofocus sensor (22) may be provided inside the camera body, as shown in the figure, and its output may be used to control the lens drive motor (2). (2) is a strobe. , and the camera timing control circuit a5 to perform a dimming operation by exchanging necessary signals such as a charge completion signal and a trigger signal.

The operation of the camera timing control circuit C15 is performed by a synchronization signal generation circuit (25) for scanning the image sensor (8).
, receives horizontal and vertical synchronization signals, and is controlled based on these signals.

In addition to this, the synchronization signal generation circuit (25) also includes a sensor drive circuit (26), a color separation and process amplification circuit (2 stains) that processes the output signal of the preamplifier (27), and a phase comparison circuit for the servo circuit for magnetic recording. Supply the necessary pulses to the circuit (29) as well.

The luminance signal and chroma signal generated by the matrix circuit provided at the output of the process amplifier circuit (28) are modulated and recorded amplified by the recording modulation circuit (30), and recorded on the magnetic sheet C321 by the head Gυ. .

The six switching circuits (33), H, C35) are
It is used to switch signals during recording and reproduction, and each switching circuit is electrically connected to the terminal R side during recording and to the terminal P side during reproduction.

In this embodiment, a reproduction demodulation circuit (36) is provided within the camera body, and the luminance signal of the reproduced video signal can be checked on the electronic viewfinder (9).

In addition, the reproduced video signal is input to the synchronization separation circuit C37),
By comparing the separated synchronization signal with a reference synchronization signal, rotation servo is applied during playback.

Phase comparison circuit c! The output of 9) is amplified by an amplifier (support) to drive a motor (three wings).A phase and rotation speed detector (40) is connected to the motor (39) through a common shaft, and the detector ( 4U) is connected to the peripheral circuit ≠υ and is used for servo control during recording.

The magnetic recording section is provided with a head feeding mechanism (6) and its drive circuit (g), a mounting mechanism for attaching and detaching the disk, and a disk positioning mechanism (g).

□□□ is a switch for setting various conditions (shutter time, etc.) for the V series switch 11, and a warning and display circuit.

Further, (9) is a power supply circuit including batch IJ, &.

Figure 3 (cLXJ) shows the operation timing at the time of shutter release of the imaging device of the present invention in this electronic snal camera, and the shutter speed in Figure 6 (LL) is 1/60 as in Figure 1 (αX8). Second, Figure 6 (6) is 11
It is 500 seconds.

The difference between Fig. 6 (,) and Fig. 1 (α) is that as shown in the figure, the shutter-first fish starts running before the sensor (8) scans for discharging unnecessary charges, or the shutter-rear curtain starts moving. The point is that readout of the signal charges is started before the running of the signal is completed.

However, what must be observed here is that the effective imaging surface of the front curtain of the shutter is the point at which the last negative charge is discharged prior to exposure.
This is before the point where the trailing curtain crosses the two ends (by time δ1), and after the trailing curtain crosses the lower end of the direct imaging surface (after time δ2), scanning for reading out the signal charges begins.

The time δ1 needs to be set with some margin because there is always a delay time and variation in running speed from the electrical front curtain running start signal until the front curtain actually starts running.

Therefore, the delay time δ0 from the start of the last vertical scan for discharging unnecessary charges to the time when the leading curtain actually starts running.
The budget will also be set with this allowance in mind.

This also applies to the running of the trailing curtain, and the time from the electrical exposure completion trailing curtain running start signal until the trailing curtain actually passes the lower end of the effective imaging surface also varies.

Therefore, the time θ3 from the start of running of the trailing curtain to the start of scanning for signal readout must be longer than a certain amount of time.

In FIG. 3, the running time of the shutter curtain is set to about 8 m5ec. Also, if the sensor (8) has an effective imaging surface of 2/6 inch size, the effective imaging surface width in the figure is 6.6 mm, and a shutter travel range of 10 circles is sufficient. It is.

By performing the above driving fx, it became possible to shorten the conventional accumulation time by 71,760 seconds.

FIG. 6(b) shows the high speed shutter (11500 seconds). In this case, it is known that there is no need to completely (stop) the scanning of the sensor.

Of course, as mentioned above (for example, when using a rotating magnetic recording disk as a recording medium), it is not possible to write to the recording medium before the trailing curtain has completed traveling, but even in that case, before the discharge of unnecessary charges prior to exposure is completed. By running the leading curtain, it is possible to lengthen the time from the completion of running of the trailing curtain to writing, which has the advantage of allowing more time to damp the vibrations caused by the trailing curtain.

Further, as is clear from FIG. 6, it is desirable that the shutter curtain speed be approximately the same as the vertical scanning speed of the sensor from the viewpoint of shortening the accumulation time. A slow shutter curtain speed is desirable because it further reduces vibration energy, but in reality,
This should be determined based on the stability of the slit width formed by the leading and trailing curtains and the shutter efficiency.

Figure 4 is a timing chart of the main signals during imaging in the present invention, with the alphabet (α) in front of each signal.
-(g) correspond to the symbols given to the signal lines of the circuit in FIG.

That is, (cL) is vertical synchronization number a, which is a pulse that is generated once every vertical scan of the sensor (3).

(b) is a pulse generated when the shirt release button is pressed. After this release switch signal (b) is generated, the aperture, which had been open until then, starts to close down to a predetermined position in synchronization with the first synchronization signal.
A signal (c) is generated to flip up the mirror.

After the above operations are completed, a start signal (e) for the leading curtain is generated, and the leading curtain begins to start. At this time, as mentioned above, the sensor clock is provided, and unnecessary charges are discharged from the sensor.

After this evacuation is complete, sensor scanning is stopped. During this time, a trailing curtain start signal (f) is generated (1) and acts on the electromagnetic magnet that locks the trailing curtain to start the trailing curtain.

Once exposure is complete, signals are read out from the sensor during the next field for recording. Signal (g) is a gate signal that enables recording at that time.

In this case, of course, as described above, reading can be started while the trailing curtain has not completed running.

As described above, according to the present invention, it is possible to shorten the time from the completion of exposure preparation to the start of exposure of an electronic still camera using a focal plane shutter and a solid-state image pickup device, and the accumulation time of signal charges from completion of exposure to readout. This has the advantage of being able to reduce signal deterioration due to the shadow current of the occult image element.

[Brief explanation of drawings]

Figure 1 (tLX) is a line diagram showing the shutter drive timing of a conventional imaging device, Figure 2 is a block diagram showing an example of an electronic still camera to which the imaging device of the present invention is applied, and Figure 6 (α) 4) is a diagram showing the shutter drive timing of the imaging device of the present invention, and FIG.
1 is a time chart showing the waveforms of each part. (1): Shooting lens system, (7): Focal plane shutter, (8): Image sensor, α→: Camera timing control circuit, Q→: Shutter drive mechanism, Han: Shutter drive circuit, (25): Synchronization signal Generation circuit, 126)
:Sensor drive circuit. Agent Patent attorney Kimura Sanroki, 3rd Ward (θ) (ITJ) Name: C: 54

Claims (3)

[Claims] (1) In an imaging device that combines a solid-state image sensor and a focal plane shutter that read out signal charges by sequential scanning in the vertical direction, the vertical scanning direction of the solid-state image sensor and the front and rear curtains of the focal plane shutter are combined. An imaging device using a focal plane shutter, characterized in that the running direction of the curtain is made to coincide with the running direction of the curtain. (2) A patent characterized in that the front curtain of the focal plane shutter starts running before the vertical scanning of the solid-state image sensor, which is performed for the last discharge of unnecessary charges prior to photographing exposure, is completed. An imaging device using the focal plane shutter according to claim 1. (3) Signal reading from the solid-state image sensor is started before the rear curtain travel of the focal plane shutter is completed.
An imaging device using the focal plane shutter according to any one of Items 1 and 2.