JP2530352B2 - Still video camera - Google Patents

Description

The present invention relates to a still video camera, and more specifically,
The present invention relates to a still video camera capable of accurately adjusting exposure when strobe light is emitted.

(Background of the Invention) A solid-state image sensor such as a CCD is used as a light receiving element of a still video camera. In this type of still video camera, image information is converted into an electric signal and further stored in an information recording medium such as a magnetic disk. Therefore, unlike the silver salt film camera, there is an advantage that development is unnecessary and image information can be transmitted to a remote place.

When a still video camera of this type is used to emit light from a strobe to capture an image of a subject, it is necessary to control the exposure amount with high accuracy. The reason for this is that in the case of a CCD, if the exposure amount exceeds the optimum amount even a little, the bright part of the image becomes white, and if the exposure amount decreases even less than the optimum amount, the dark part of the image becomes black. In the case of the conventional silver salt film, even if the exposure is slightly deviated from the optimum value, it can be corrected at the time of development or printing. Therefore, in the case of a conventional still camera, exposure control is performed by first determining the distance to the subject by autofocus (automatic focus adjustment) based on the formula: guide number = distance x aperture, and then determining the aperture from the above formula. It could be done relatively easily (called flashmatic control). In addition, the number of distance steps should be set to about 8 steps from ∞ (infinity) to 1 m.

On the other hand, in the case of a still video camera using a CCD as a light receiving element, the optimal exposure control is impossible because the latitude of the CCD is narrow in the flashmatic control as described above. Therefore, in the case of an electronic still video camera, it is necessary to control the exposure with high accuracy. For example, the light emission amount of the strobe is controlled using a light control strobe.

FIG. 5 is a configuration diagram showing a configuration example of an exposure control system of a conventional electronic still video camera. When a trigger (light reception start signal) enters the light emission control unit 1, the light emission control unit 1 causes the strobe 2 to emit light. The subject 3 is illuminated by the light emitted from the strobe 2, and the reflected light of the subject 2 is received by the light receiving lens 4
It is incident on the light receiving element 5 via. The integrating circuit 6 integrates the photoelectric conversion output of the light receiving element 5 at the same time as strobe light emission. When the output of the integrating circuit 6 reaches the dimming level determined by the sensitivity of the CCD and the selected diaphragm, the comparator 7 applies a stop signal to the light emission control unit 1. Thereby, the light emission control unit 1 stops the light emission operation of the strobe 2.

FIG. 6 is a characteristic diagram showing the conversion characteristic of the flash emission amount at this time. In the figure, the vertical axis is the flash emission amount,
The horizontal axis represents time t. A trigger is applied at time t ₁ , and the strobe light emission amount rapidly increases as shown in the figure.
Then, at time t _S , when the integrated value of the integrating circuit 6 reaches the dimming level, the strobe 2 stops emitting light. The shaded area in between is the actual amount of light emission. The broken line in the drawing is the emission curve of the strobe at the time of full emission. Assuming that the time at which the amount of light emission at full light emission becomes zero is t ₂ , it suffices that t ₂ be later than t _S , and the camera sets a fixed time (for example, 1/60 second). Then, t _{1 to} t ₂ is the maximum integration time of the integrating circuit 6.

In a solid-state image pickup device having a photosensor section, a transfer section, and a gate section for transferring the accumulated charges of the photosensor section to the transfer section, the timing at which the gate section is brought into a conductive state is made variable to achieve an appropriate exposure amount. There is also a method in which exposure control is performed by applying a gate pulse to the gate unit at the point of time to make the gate unit conductive and reading out the accumulated charge in the optical sensor unit.

(Problems to be Solved by the Invention) As a strobe, for example, a xenon tube is used, and as shown in FIG. The circuit configuration of the control unit 1 becomes extremely complicated, and a time lag occurs between the output of the light emission stop signal and the actual stop of light emission. For this reason, it is difficult to turn off the strobe light emission with high accuracy during the strobe light emission, and it is extremely difficult to turn off the strobe light emission with high accuracy especially at the rising portion of the light emission. As a result, even when an automatic light control strobe is used, the finished image often flies white, especially in strobe photography with the aperture opened at short distances. In addition, there is also a problem that the system becomes large due to the complicated circuit configuration and the cost of the apparatus increases.

Further, in the method of adjusting the exposure by changing the timing of the pulse applied to the gate portion in the solid-state imaging device having the optical sensor portion, the gate portion, and the transfer portion, the gate portion is brought into the conductive state at the time when the appropriate exposure amount is reached. Is giving a pulse for.

FIG. 7 is a waveform diagram showing a state of exposure control at the time of stroboscopic light emission by this type of solid-state imaging device. In this figure,
(A) shows a flash emission intensity characteristic, (b) shows a positive stop signal given at the time of proper exposure, and (c) shows a gate signal given at the time of opening / closing the shutter. Time to
Then, the exposure is started by the gate signal. Then, at t ₁ , the strobe starts emitting light, and at t ₂ , a stop signal indicating that proper exposure has been generated is generated. Based on this stop signal,
A gate signal is generated. With this gate pulse of t ₂ ,
The charges generated in the photosensor section are transferred to the transfer section, and the exposure is completed. The strobe will continue to emit light until t _S, but it will not affect the exposure.

However, since the gate pulse has a certain pulse width, the actual exposure continues until the trailing edge of the gate pulse (the pulse has a positive polarity). Further, since the electric charge accumulated in the photosensor portion is moved during this pulse period, the pulse width cannot be made too narrow. Therefore, although the light emission amount of A is sufficient, in reality, the subject illuminated with the light emission amount of A + B is photographed, resulting in overexposure. In particular, there is a problem that accurate exposure adjustment cannot be performed and the exposure tends to be overexposed in a portion where the strobe light has a sharp rise.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a still video camera capable of capturing an image with an accurate exposure amount when strobe light is emitted.

(Means for Solving the Problems) The present invention for solving the above-mentioned problems includes a solid-state image sensor having an electronic shutter function, a diaphragm unit that narrows the amount of incident light from the outside incident on the solid-state image sensor, and a solid-state image sensor. An exposure starting means for starting the exposure of the image pickup device, a strobe light emission instructing means for instructing strobe light emission after a lapse of a predetermined time based on a predetermined shunter speed, and a charge generated in the solid-state image pickup device at the time of the proper exposure. Based on the exposure ending means for ending the exposure by reading, the distance measuring means for obtaining the distance to the subject, and the strobe light emission amount exceeding at least 50% based on the distance data obtained by the distance measuring means. And an aperture control means for controlling the aperture value of the aperture means so that the proper exposure can be achieved.

(Operation) The aperture control means controls the aperture value of the aperture means by the data of the distance to the subject so that the proper exposure is achieved when the strobe light emission amount exceeds at least 50%. The strobe is caused to emit light a predetermined time after the exposure of the optical sensor section of the solid-state image sensor is started. Predetermined exposure amount (appropriate exposure amount)
The exposure is completed by reading out the electric charges generated in the solid-state image pickup device when the temperature reaches the temperature.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing an example of the configuration of an embodiment of the present invention. The same parts as those in FIG. 4 are designated by the same reference numerals. In the figure, 2 is a strobe for illuminating a subject, 3 is a subject, 6 is an integrating circuit for integrating and measuring the amount of stroboscopic light emission, and 7 is the output of the integrating circuit 6 and the dimming level are compared to adjust the integrated value. When the light level is reached, a comparator that outputs a stop signal, 10 is a light emitting circuit that emits light from the strobe 2 in response to a trigger signal from the CPU, 11 is a shooting lens for shooting a subject, and 12 is light that has passed through the lens 11. A diaphragm mechanism for narrowing the amount, 13 is a solid-state image sensor having an electronic shutter function, 14 is a solid-state image sensor control circuit that controls the exposure amount of the solid-state image sensor 13 by receiving a stop signal from the comparator 7, and 15 is normal photometry Light-receiving lens, 16 is a light-receiving element for normal photometry, 17 is a light-metering circuit that measures the brightness around the subject using the output from the light-receiving element 16 for normal light-metering, and 18 is a light metering circuit.
A CPU that determines the aperture and shutter speed and gives control signals to various circuits based on the output from 17, 19 is a strobe light receiving lens, 20 is a strobe light receiving element, and 21 is a distance measuring device that measures the distance to the subject. Circuit. Further, FIG. 2 is a configuration diagram showing the configuration of the solid-state imaging device 13. In this figure, 13a is an optical sensor section of a solid-state image sensor that stores electric charges when it receives light, and 13b is a pulse that is applied from a solid-state image sensor control circuit to move the electric charges generated in the optical sensor section to a vertical transfer section described later. / Gate switching between non-conduction and 13c
Is a vertical transfer unit that vertically transfers the charges accumulated in the photosensor unit 13a that have passed through the gate 13b, 13d is a storage unit for storing the charges transferred from the vertical transfer unit 13c, and 13e is a storage unit 13d.
It is a horizontal transfer unit that horizontally transfers and outputs electric charges from the. Although only one row is shown in this drawing for the optical sensor section, the gate, and the vertical transfer section, it is actually assumed that a plurality of rows are provided.

First, the distance measuring circuit 21 obtains the distance to the subject 3. The CPU 18 obtains aperture data based on this distance data. Here, the aperture data is calculated so that the appropriate exposure amount is obtained in the latter half of the flash emission. This operation is as follows.

Aperture = strobe guide number / distance For example, assuming that the solid-state image sensor 13 has an ISO sensitivity of 100 and the strobe guide number GNo. Is 10, the relationship between the distance and the aperture is as follows.

0.5m to 0.9m F11 0.9m to 1.8m F5.6 1.8m to 3.6m F2.8 In this way, 50% to 100% of the flash output,
The exposure amount is appropriate. The diaphragm mechanism 12 is controlled based on the diaphragm data thus obtained.

When a strobe having a peak emission intensity immediately after light emission is used, the aperture may be adjusted so that the appropriate exposure amount is reached when the strobe emission intensity peak is passed.

Similar to FIG. 7, description will be made with reference to the waveform chart shown in FIG. A curve f shown in FIG. 3 is a stroboscopic light emission curve when the stroboscopic light is fully emitted. In the present invention, based on the shutter time (for example, 1/60 second corresponds to t ₀ to t _S in the figure in the case of 1/60 second) in the preset flash mode, the maximum flash emission time t from the time t _S when the shutter is closed is set. _{1 to} t
_The strobe is made to emit light at time t ₁ which is short for _S (usually 50 μs to 500 μs) (the light emission amount is not controlled and full light emission is sufficient). Now, at time t ₀ , a signal is given from the solid-state image sensor control circuit 14 to the solid-state image sensor 13, and the optical sensor unit 13a (second
(Refer to the figure) The transfer of charges to the vertical transfer unit is completed and image information can be received (that is, the shutter is open).
Then, the optical sensor unit 13a starts exposure, and charging of electric charges is started.

Next, after a predetermined time has elapsed, when the CPU 18 triggers at time t ₁ , the light emitting circuit 10 causes the strobe 2 to emit light. The subject 3 is illuminated by strobe light emission. The reflected light from the subject 3 enters the stroboscopic light receiving element 20 via the stroboscopic light receiving lens 19, and enters the solid-state imaging element 13 via the taking lens 11 and the diaphragm mechanism 12. During this period, the flash emission amount increases rapidly as shown in FIG.
At the time t ₁ , the integration start signal enters the integration circuit 6 at the same time as the strobe light emission signal from the CPU 18.

The integrating circuit 6 integrates the output of the strobe light receiving element 20, and the output increases with time. Then, the output of comparator 7 is operated at the time t ₂ has been reached dimming level of a predetermined reference, and outputs a stop signal. Since the aperture is set as described above, the flash output
When it exceeds 50%, the standard dimming level is reached. The stop signal may be output from the comparator 7 through the CPU 18.

Upon receipt of this stop signal, the solid-state image sensor control circuit 14 applies a gate signal to the gate 13b (see FIG. 2) in the solid-state image sensor 13 so that the charges accumulated in the optical sensor section 13a are transferred to the vertical transfer section 13c. Transfer to. The charges in the vertical transfer unit 13c are quickly transferred to the storage unit 13d. As a result, the image information of the subject 3 in the optimal exposure state is stored in the storage unit 13d. At this time, the integration time of the solid-state image sensor 13 is t ₀ ~
It becomes t ₃ , which is shorter than the initial setting (t ₀ ~ t _S ) by (t _S −t ₃ ), but this amount is very short and (t _S −t ₀ >> t _S −t ₃ ) Also, the shutter speed in the strobe mode (for example, 1/60 second t _{0 to} t _S ) does not cause any problem because it is not a meaningful number. Also, during proper exposure
t ₂ exposure until late slightly continues from (up to t ₃₎ is, in the flash light emission amount at this portion is extremely small compared to the light emission amount of t ₁ ~t _3, not a problem.

On the other hand, the strobe 2 continues to emit light after time t ₃
It will go out after t _S. Here, the time T during which the strobe 2 emits light (from t ₁ to t _S ) is the actual integration time of the integration circuit 6. In the stroboscopic light emission characteristic curve f, the shaded portion (t _{1 to} t _S ) is the amount of exposure that is integrated into the solid-state image sensor 22 to form an image, and does not contribute to image formation thereafter. Exposure amount.

FIG. 4 is a waveform diagram showing the case where strobes having different light emission characteristics are used. A curve f shown in this figure is a stroboscopic light emission curve when the stroboscopic light is fully emitted. Unlike the emission characteristics shown in FIG. 3, the emission peak is in the latter half of the emission period. Even in this case, the aperture is adjusted so that the proper exposure is obtained when the flash light emission amount exceeds 50%. Therefore, the exposure ends at the timing when the change in the strobe light emission intensity is small (t _{3 in} FIG. 4).

The exposure to slightly slower than the proper exposure time t ₂ is continued (up to t ₃₎ is, strobe light emission amount at this portion t ₁ ~
It is extremely small compared to the amount of light emission at t ₃ , and does not pose a problem.

On the other hand, the strobe 2 continues to emit light after time t ₃
It will go out after t _S. In the stroboscopic light emission characteristic curve f, the shaded portion (t _{1 to} t ₃ ) is the amount of exposure that is integrated by the solid-state image sensor 22 to form an image, and the amount of exposure that does not contribute to image formation thereafter. Is the amount.

In this way, the method of storing the charge charge amount at the time when the optimum exposure amount is reached in the storage unit by using the electronic shutter function of the CCD is adopted without taking the method of stopping the stroboscopic light emission, which is difficult to control. Then, the optimum exposure amount is reached at the timing when the change in the stroboscopic light emission intensity is small. As a result, the exposure amount can be controlled with high accuracy with a simple configuration when the flash fires.

As described above, in the present invention, the aperture is adjusted so that the appropriate exposure amount is reached when the strobe light emission amount exceeds at least 50%. The error of the light quantity is extremely small. In addition, since a large amount of a component having a high color temperature is emitted at the time of the rise of strobe emission, a bluish image may be obtained when shooting is performed using only this component. In the present invention, the light in the latter half of the flash emission amount (light of a component having a low color temperature) is also used, so that a well-balanced neutral color tone is obtained.

In addition, although the case where the FIT-CCD is used is described in the above embodiment, the present invention is not limited to this, and the same effect can be obtained by using the interline CCD.

(Effect of the Invention) As described in detail above, according to the present invention, the aperture is adjusted so that the proper exposure amount is reached when the stroboscopic light emission amount exceeds at least 50%, and when the proper exposure amount is reached. By ending the exposure of the solid-state image pickup device, it is possible to realize a still video camera capable of taking an image with an accurate exposure amount when strobe light is emitted.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram showing a main part of a solid-state image sensor, FIG. 3 is a waveform diagram showing the operation of the present invention, and FIG. FIG. 5 is a waveform diagram showing the operation of another embodiment, FIG. 5 is a configuration diagram showing a configuration example of a conventional device, FIG. 6 is a strobe light emission characteristic diagram of the conventional device, and FIG. 7 is a waveform diagram when strobe light emission of the conventional device. Is. 2 ... Strobe, 3 ... Subject, 6 ... Integrator circuit, 7 ... Comparator, 10 ... Light emitting circuit, 11 ... Shooting lens, 12 ... Aperture mechanism, 13 ... Solid-state image sensor, 14 ... Solid-state image sensor control circuit 15 …… Receiving lens for normal photometry 16 …… Receiving element for normal photometry 17 …… Photometry circuit, 18 …… CPU 19 …… Receiving lens for strobe light 20 …… Receiving element for strobe light 21 …… Distance measuring circuit

Claims (1)

(57) [Claims] 1. A solid-state image sensor having an electronic shutter function, diaphragm means for reducing the amount of incident light from the outside that is incident on the solid-state image sensor, and exposure start means for starting exposure of the solid-state image sensor. Strobe light emission instructing means for instructing strobe light emission after a lapse of a predetermined time based on the shutter speed, an exposure end means for ending the exposure by reading the electric charge generated in the solid-state image sensor at the time of proper exposure, and an object Based on the distance measuring means for obtaining the distance to the distance measuring means and the distance data obtained by this distance measuring means, the aperture value of the aperture means is adjusted so that the proper exposure is achieved when the flash emission amount exceeds at least 50%. A still video camera, comprising: an aperture control unit for controlling.