JPH0690397A - Video camera and its focusing method - Google Patents

Abstract

PURPOSE:To attain proper focus control using a video signal outputted from a CCD even in the case of a low luminance object. CONSTITUTION:A YL synthesis circuit 15 extracts a luminance signal component from a video signal outputted from a CCD 4 and a luminance of an object is measured based on the luminance signal component. When the luminance level of the object is a prescribed level or lower, a discharge tube 45 is used to implement preliminary lighting and a high frequency component for range finding is extracted from the video signal outputted from the CCD 4 by using a BPF 20. The focus control for an image pickup lens 3 is implemented based on the extracted high frequency component.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video camera (still / automatic focusing control using a video signal obtained by preliminarily photographing an incident light image using a solid-state electronic image pickup device).
(Including movie video cameras and still video cameras) and focusing methods thereof.

[0002]

2. Description of the Related Art Some video cameras have various automatic focusing functions (so-called AF functions), and among them, an optical image incident by a solid-state electronic image pickup device such as CCD is preliminarily photographed and There is one that performs focus control using the obtained video signal.

However, when the subject has a low luminance, the level of the video signal output from the solid-state electronic image pickup device becomes low. For this reason, the reliability of the focus control becomes low, and proper focus control may not be performed.

[0004]

DISCLOSURE OF THE INVENTION It is an object of the present invention to enable proper focusing control by using a video signal output from a solid-state electronic image pickup device even for a low-luminance subject.

The present invention relates to a video / optical system including an image pickup lens and an image pickup optical system including a solid-state electronic image pickup device for converting an optical image incident through the image pickup lens into a video signal and outputting the image signal.
In a camera, a high frequency component for focus detection is extracted from a video signal output from the solid-state electronic image pickup device, and focus control means for performing focus control of the image pickup lens from the extracted high frequency component, and subject brightness are measured. Photometric means, judgment means for judging whether or not the level of subject brightness measured by the photometric means is below a predetermined level at which focusing control by the focusing control means is impossible, and projecting auxiliary light on the subject And an auxiliary light source for determining that the auxiliary light source is below the predetermined level, the auxiliary light source is used to project auxiliary light onto the subject, and the focusing control means is used to perform the focusing control. It is characterized by comprising control means for controlling.

Further, according to the present invention, there is provided an imaging lens, an imaging optical system including a solid-state electronic imaging device for converting an optical image incident through the imaging lens into a video signal and outputting the video signal, and a video signal output from the solid-state electronic imaging device. A video camera equipped with a focus control means for extracting a high-frequency component for focus detection and controlling the focus of the imaging lens from the extracted high-frequency component measures the subject brightness and measures the measured subject brightness. It is determined whether or not the level is lower than or equal to a predetermined level at which the focus control processing by the focus control means is impossible, and when it is determined to be lower than or equal to the predetermined level, auxiliary light is projected onto the subject, and the focus control means Is performed, and the focusing control process based on the extracted high frequency component is performed.

According to the present invention, the auxiliary light is projected onto the subject when the focusing control by the focusing control means is impossible. Therefore, the level of the video signal output from the solid-state electronic image pickup device becomes high, and the focus control processing using the video signal becomes possible. Even if the subject brightness is low, it becomes possible to perform appropriate focusing control based on the video signal.

In the above, it is preferable that the auxiliary light is projected from the stroboscopic light emitting device and is controlled so that the emitted light amount becomes constant.

Further, auxiliary light may be projected from the red light emitting element. When the solid-state electronic image pickup device is provided with a color filter, it is preferable to use a red light emitting device having the same wavelength as the red spectrum of the color filter.

Further, the measurement of the subject brightness is performed by extracting a component related to the brightness signal from the video signal output from the solid-state electronic image pickup device (for example, a component other than the brightness signal, which can be regarded as a brightness signal such as a green signal) It may be performed based on the above, or may be performed by a photometric element.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment in which the present invention is applied to a digital still camera will be described below in detail with reference to the drawings.

FIG. 1 is a block diagram of a digital circuit of an embodiment of the present invention.
It is a block diagram which shows the electric constitution of a still camera.

The imaging optical system includes a diaphragm 2, an imaging lens 3,
And a CCD 4 as a solid-state electronic image sensor (image sensor). A mechanical shutter is provided if necessary, but generally the shutter function is achieved by an electronic shutter realized by the control of the CCD 4. The image pickup lens 3 forms a subject image on the CCD 4,
It is moved by the imaging lens driving device 25 controlled by the CPU 5 and positioned at the in-focus position.

In this embodiment, a photometric sensor 26 is provided for preliminary photometry, and a range finding sensor 27 is provided for preliminary range finding. The photometric data and range finding data from these sensors 26 and 27 are stored in the CPU 5. Given. CPU5
Controls at least one of the aperture value and the shutter speed on the basis of the photometric data obtained from the photometric sensor 26 so that the exposure amount to the CCD 4 falls within a substantially appropriate range. The CPU 5 also positions the image pickup lens 3 in the vicinity of the in-focus position via the image pickup lens driving device 25 based on the distance measurement data from the distance measurement sensor 27.

After the rough exposure amount adjustment based on the preliminary photometry and the rough focusing control based on the preliminary distance measurement, the preliminary photographing is performed. By this preliminary shooting CCD
The calculation of the photometric value, the precise exposure control, and the highly accurate focusing control are performed by using the video signal obtained from No. 4. These highly accurate exposure control and focusing control will be described in detail later.

The digital still camera is for indoor shooting,
As will be described later, a strobe device is included so that an appropriate exposure amount can be obtained when auxiliary light is required. This strobe device is driven by a power supply 41.

The strobe device is a discharge tube (strobe) 45
And a charging circuit 40 for charging the electric charge given to the discharge tube 45.
And a light emission quantity control circuit 30 for controlling the quantity of strobe light emission, and a stop circuit 46 for stopping the light emission of the discharge tube 45.

The voltage of the power source 41 is boosted by the boosting circuit 42 and the main capacitor 43 is charged. The charging voltage of the main capacitor 43 is supplied to the CP via an appropriate voltage reducing circuit or voltage detecting circuit.
It is detected by being applied to the A / D port of U5. This allows the CPU 5 to know that charging of the main capacitor 43 has been completed.

Since the CPU 5 can detect the charging voltage of the main capacitor 43, the charging voltage of the main capacitor 43 before the discharge tube 45 emits light and the main capacitor 43 after the discharge tube 45 emits light.
It is also possible to detect each of the charging voltage and the charging voltage and to calculate the amount of light emitted from the discharge tube 45 from the difference between these voltages.

Strobe light emission is performed by giving a strobe light emission command X ON to the trigger circuit 44. When the strobe light emission command X ON from the CPU 5 is given to the trigger circuit 44, the trigger circuit 44 is driven, the electric charge accumulated in the main capacitor 43 is discharged through the discharge tube 45, and strobe light emission starts.

The emitted light quantity control circuit 30 includes an electronic volume circuit (EVR) 31 including a D / A converter 31A for converting the data representing the emitted light quantity output from the CPU 5 into a corresponding voltage and outputting it. ing. Also included is a differential amplifier circuit 36 for providing a stop signal to stop circuit 46.

Further, the emission power control circuit 30 includes a reference power source 32.
And a capacitor 34 is included. The output voltage of the EVR 31 is given to the capacitor 34 via the resistor 33. A switch 35 for discharging the charge of the capacitor 34 is also provided. A reference power supply circuit is provided at the negative input terminal of the differential amplifier circuit 36.
The reference voltage output from 32 is applied, and the differential amplifier circuit 36
The terminal voltage of the capacitor 34 is applied to the positive input terminal of the.

The switch 35 is normally turned on, and CP
It is turned off when the flash emission command X of U5 is given. When the switch 35 is turned off, the EV
Charging of the capacitor 34 is started based on the voltage output from R31.

A voltage is output from the EVR31 and the switch 35
When is turned on, a predetermined charge is accumulated in the capacitor 34. When the terminal voltage of the capacitor 34 becomes equal to the reference voltage output from the reference power supply 32, a stop signal is output from the differential amplifier circuit 36 and is given to the stop circuit 46, so that the discharge tube 45 stops emitting light.

In the CCD 4, interlace photographing is performed by the substrate extraction pulse, the A field vertical transfer pulse, the B field vertical transfer pulse and the horizontal transfer pulse, and the A field and B field image signals (GRGB
Color sequential signals) are alternately generated every one field period and sequentially read out. The driving of the CCD 4 (imaging and reading of a video signal) is performed at least at the time of photographing, and for precision photometric processing and distance measuring processing prior thereto.

The video signals of the A field and the B field representing the subject image output from the CCD 4 are passed through a correlated double sampling circuit (CDS) 7 to a color separation circuit 8
Given to three primary colors, G (green), R (red) and B
It is separated into (blue) color signals.

The color signals G, R and B are given to a variable gain amplifier circuit (hereinafter referred to as GCA) 9. In Figure 1, GC
Although one block is shown as A9, GCA is actually provided for each of the R, G, and B signals. In this GCA 9, after correction of variations in light transmittance of the color filters provided in the CCD 4 between filters (hereinafter referred to as color filter variation correction) and white balance adjustment are performed, the gamma correction circuit 10
Given to. This is to perform focusing control described later with high accuracy. For the purpose of focusing control, at least color filter variation correction may be performed, but it is more preferable to perform white balance adjustment in addition to this.

The output color signals R, G, B of the GCA 9 are gradation-corrected by the gamma correction circuit 10 and input to the clamp and resampling circuit 11.

The clamp and resampling circuit 11 is
The three color signals R, G, B are clamped and re-converted into color sequential signals of GRGB ... Which match the color filter arrangement in the CCD 4. This color sequential signal is input to the gain control and blanking circuit 12. The gain control and blanking circuit 12 amplifies the color sequential signal to an appropriate level for recording and adds the blanking signal to it. The output signal of the gain control and blanking circuit 12 is given to the first input terminal S1 of the changeover switch 13.

Prior to the main photographing, precise photometric processing (exposure control) and focusing control are performed as described above. The photometric processing is carried out by utilizing the low frequency component of the video signal obtained from the CCD 4 by preliminary photography, and the focusing control is carried out by utilizing the high frequency component of the above video signal.

In order to extract the low frequency component of the video signal representing the image in the photometric area (described later) provided in the photographing area of the CCD 4 for the photometric processing, the Y _L synthesizing circuit 15,
A gate circuit 16, an integrating circuit 17, and an amplifying circuit 18 are provided. The output signal of the amplifier circuit 18 is the second signal of the changeover switch 13.
Input terminal S2.

On the other hand, for focusing control, in order to extract a high frequency component of a video signal representing an image in a distance measuring area (described later) provided in the photographing area of the CCD 4, a gate circuit is used.
19, band pass filter (hereinafter referred to as BPF) 2
0, a detection circuit 21, an integration circuit 22, and an amplification circuit 23 are provided. The output signal of the amplifier circuit 23 is given to the third input terminal S3 of the changeover switch 13.

The changeover switch 13 is controlled by the CPU 5, and has a gain control and blanking circuit 12,
Either one of the output signals of the amplifier circuit 18 and the amplifier circuit 23 is selected and output. The output signal of the changeover switch 13 is A /
It is given to the D converter 14 and converted into digital data.

In the photometric processing and focusing control prior to the main photographing, the changeover switch 13 selects and outputs the input signal of either the input terminal S2 or S3.

The main photographing is performed after the photometric processing, the exposure control (control of the diaphragm and the shutter) based thereon, and the focusing control (positioning of the image pickup lens 3). At this time, the changeover switch 13 is changed over so as to select the input terminal S1. The video signal obtained from the CCD 4 by the actual photographing is inputted to the A / D converter 14 through the circuits 7, 8, 9, 10, 11, 12 and the changeover switch 13 described above, and the A / D converter 14 produces a digital image. After being converted into data and processed by an image data processing circuit (not shown) such as Y / C separation and data compression, it is recorded on a recording medium such as a memory card.

Of the photometric processing (and exposure control based on it) and the focus control prior to the main photographing, the photometric processing will be described first.

The photometric processing is performed by the Y _L synthesizing circuit 15, as described above.
This is performed using the gate circuit 16, the integration circuit 17, and the amplification circuit 18. The Y _L synthesizing circuit 15 outputs the output color signal R of the GCA 9,
G and B are given.

The CPU 3 outputs a window signal WIND1 for controlling the gate circuit 16 and a reset signal HLRST1 for resetting the integrating circuit 17. These signals WI
The timing of ND and HLRST will be described later.

The color signals R, G and B output from the GCA 9 are added by the Y _L synthesizing circuit 15 to generate a relatively low frequency luminance signal Y _L (hereinafter simply referred to as luminance signal Y _L ). The luminance signal Y _L passes through the gate circuit 16 while the window signal WIND1 is applied during the required horizontal scanning period. The integrator circuit 17 has a reset signal HLRS.
It is reset when T1 is given, and then the luminance signal Y _L input from the gate circuit 16 is integrated. Integrator circuit 17
The integrated signal of is amplified by the amplification circuit 18, and then the integration circuit 17
Immediately before being reset, the data is input to the A / D converter 14 via the change-over switch 13, converted into digital integrated data for photometry by this A / D converter 14 and taken into the CPU 5.

In the photometric processing of this embodiment, average photometry (hereinafter referred to as A
V metering) and spot metering (hereinafter referred to as SP metering) for measuring the brightness of the main subject in the field of view. The SP metering is useful when the brightness of the main subject and the background in the field of view are different and it is necessary to set an appropriate exposure condition accordingly.

Further, in this embodiment, the integration by the integration circuit 17 and the A / D conversion operation and addition processing by the A / D converter 14 are alternately performed every horizontal scanning period.

FIG. 2 shows an AV photometric area and an SP photometric area set in the photographing area 50 of the CCD 4.

The AV photometric area is basically set over almost the entire photographing area 50. In this embodiment, the AV photometric area is set for a period of 40 μs after the lapse of 16 μs from the trailing edge of the horizontal synchronizing signal HD (the start point of the horizontal scanning period) in the horizontal direction, and the 35th horizontal scanning in the vertical direction. 24th from the line
It is set up to the 6th horizontal scan line.

The SP metering area is set as a small area at an arbitrary position within the photographing area 50. In this embodiment, the SP metering area is set at the center of the photographing area 50, and the horizontal direction is the 87th horizontal scanning line in the vertical direction during the period of 15 μs after 28.5 μs has elapsed from the fall of the horizontal synchronizing signal HD. From the 194th
It is set up to the second horizontal scan line.

The memory associated with the CPU 5 is provided with a photometry area and a distance measurement area. AV metering area data area and SP metering area data
There is an area.

When AV photometry is performed, integration is performed every other horizontal scanning line in the AV photometry area.
The above integration is performed every other horizontal scanning line for A / D conversion, reset integration of the integration circuit, and data addition processing.

As shown in FIG. 3, in the AV photometry, the gate circuit 16 receives 16 μs after the trailing edge of the horizontal synchronizing signal HD between the 34th horizontal scanning line and the 246th horizontal scanning line. A window signal WIND1 having a pulse width of 40 μs is applied. Then, the integrating circuit 17
Integration of the luminance signal Y _L , A / D conversion of the integration signal in the horizontal scanning period subsequent to the horizontal scanning period in which this integration operation is performed, reset of the integration circuit 17 and AV of the memory.
The addition of integrated data to the photometric area data area is alternately repeated for each horizontal scanning period.

When SP photometry is performed, a pulse width rises 28.5 μs after the falling edge of the horizontal synchronizing signal HD in the gate circuit 16 between the 87th horizontal scanning line and the 194th horizontal scanning line. A window signal WIND1 of 15 μs is provided.

Also in SP photometry, when the window signal WIND1 having a pulse width of 15 μs is given to the integrating circuit 17 and the luminance signal Y _L is integrated, the integration is performed in the horizontal scanning period subsequent to the horizontal scanning period in which the integration operation is performed. A / D conversion of the signal, reset of the integrating circuit 17, and addition of the integrated data to the SP photometric area data area of the memory are performed.

When AV photometry is performed, the CPU 5 adds integrated data for one horizontal scanning line obtained based on the window signal WIND1 having a pulse width of 40 μs in the AV photometry area data area for one field period by the procedure described later. Then, the AV photometric value is calculated.

When SP metering is performed, the CPU 5
The integrated data for one horizontal scanning line obtained based on the window signal WIND1 having a pulse width of 15 μs is added in the SP metering area data area for one field period by the procedure described later to calculate the SP metering value.

Next, focusing control will be described.

Referring again to FIG. 1, the output signal of the gain control and blanking circuit 12 is the gate circuit 19
To enter. The gate circuit 19 is controlled by the window signal WIND2 given from the CPU 5. gain·
The output signal of the control and blanking circuit 12 passes through the gate circuit 19 and BPF20 during the period in which the window signal WIND2 is given in the required horizontal scanning period.
To enter.

The BPF 20 extracts a high frequency component required for focusing control from the input signal, and the output signal of the BPF 20 is input to the detection circuit 21. The high frequency component signal output from the BPF 20 is detected by the detection circuit 21, integrated by the integration circuit 22, and further amplified by the amplification circuit 23. Then, when the changeover switch 13 selects the input terminal S3, A / The data is input to the D converter 14, converted into digital data for focusing control by the A / D converter 14, and then converted into C
Captured by PU5.

The digital data supplied from the A / D converter 14 is integrated data obtained by integration over a horizontal scanning period of a focus detection area, which will be described later, set in the photographing area, and the CPU 5 is the integrated data. Is added over the vertical scanning period of the focus detection area to calculate focus detection data, and focus control is performed based on this data. Details will be described later.

Generally, when the image is out of focus and out of focus, the high frequency component contained in the video signal obtained from the CCD by photographing is small. When the image comes into focus, the high-frequency component of the video signal increases, and the high-frequency component contained in the video signal becomes maximum at the correctly focused position. In this embodiment, focusing control is performed based on such a fact, and the BP
F20 has about 1.5 to extract high frequency component of video signal.
A pass band of 2.5 MHz is set.

FIG. 4 shows a focus detection area set in the photographing area 50 of the CCD 4. This focus detection area is set at the center of the shooting area 50 where the main subject is highly likely to exist. In this embodiment, the horizontal direction is set as an area smaller than the SP photometric area shown in FIG. Of course, it goes without saying that the focus detection area can be set to any location within the shooting area 50 and to any width.

As shown in FIG. 5, a window signal WIND2 having a pulse width of 10 μs is applied to the gate circuit 19 after 31 μs has elapsed from the falling edge of the 87th horizontal synchronizing signal HD, and as described above, this window signal WIND2 is supplied. WIND2
, The gate circuit 19 passes the output signal of the circuit 12. The high frequency component signal taken out by the BPF 20 is given to the integration circuit 22 via the detection circuit 21 and integrated.
The integrated output signal of the integrating circuit 22 is passed through the amplifying circuit 23 and the changeover switch 13 and then, in the next horizontal scanning period, the A / D converter
It is converted into digital data by 14 and given to the CPU 5. The integrating circuit 22 is reset by the reset signal HLRST2 after the A / D conversion process. CPU5 is
This digital data is added to the previous data in the distance measuring area of the memory (which is zero because it is cleared in the first case) and stored. The distance measuring area is cleared in synchronization with the 86th horizontal synchronizing signal HD or at the start of the field.

As described above, the high-frequency component signal is detected by the BPF 20 on one horizontal scanning line in the focus detection area, the high-frequency component signal is detected and integrated, and the integrated signal is A / D converted and horizontally. The addition of integrated data in the scanning period is alternately repeated every horizontal scanning period. Then, this repetition is performed until the 194th horizontal scanning period, that is, over the entire area within the focus detection area.

Therefore, at the time when the scanning in the focus detection area is completed, the focus detection area of the memory shows the focus detection addition indicating the integral value of the high frequency signal passing through the BPF 20 over the entire focus detection area. The data has been stored.

As described above, in the preliminary distance measurement using the distance measuring sensor 27, the approximate distance to the subject is measured. Based on this preliminary distance measurement data, the imaging lens 4 is considered to be the in-focus position, which is a little before this position (called the initial position).
Is delivered to.

The integration operation over the focus detection area of the high frequency component of the video signal output from the CCD 4 is performed by the imaging lens 3
Is carried out at least 6 times (that is, in the B field period of each frame period over 6 frame periods) while feeding forward by 10 μm. First, the first focus detection addition data is obtained at the above initial position (the amount of extension of the imaging lens 3 = 0 μm). In the next frame period, second focus detection addition data is obtained at a position (image pickup lens extension amount = 10 μm) in which the image pickup lens 3 is extended by 10 μm from the initial position. In the same way, the imaging lens 24
The third to sixth focus detection addition data are obtained while feeding each 10 μm. The 6-position addition data thus obtained is stored in a predetermined area of the memory as shown in FIG.

FIG. 7 is a graph showing the focus detection addition data at the six positions shown in FIG. The initial position of the imaging lens 3 is slightly before the true focus position. From this position, the image pickup lens 3 is extended by 10 μm, and focus addition data is obtained. The integrated value of the high frequency signal included in the video signal becomes maximum at the true focus position. Imaging lens 4
The unit feeding amount of is 10 μm, which is a very small distance.
Even if the position where the focus detection addition data shows the maximum value is regarded as the true focus position, the error is extremely small. Therefore, the image pickup lens 3 is placed at a position where the focus detection addition data shows the maximum value.
High-precision focusing can be achieved by positioning.

FIGS. 8A and 8B are time charts showing the exposure control and focusing control based on the preliminary photographing and the timing of the main photographing. Figure 8 (A) and (B)
The time chart shown in () shows the case where the subject has low brightness and pre-light emission is performed by the strobe device to perform focusing control based on preliminary shooting.

9 and 10 show the overall procedure of the preliminary photometry, the preliminary distance measurement processing, and the exposure control and focusing control based on the preliminary photographing performed thereafter.

At time t ₁ , the shutter release button (not shown) is pressed down in the first step (S1) to perform preliminary photometry based on the photometry signal from the photometry sensor 26 and based on the range finding signal from the range finding sensor 27. Preliminary distance measurement is performed (step 70). The exposure conditions are initialized based on the preliminary photometry (step 71), and the imaging lens 3 is extended to the initial position based on the preliminary distance measurement (step 72).

Next, the changeover switch 13 is connected to the input terminal S2 (step 73). As a result, in the period between time t ₁ and time t ₂ , the CCD 4
The photometry and the calculation of the photometric value are performed based on the video signal output from (steps 74 and 75).

It is judged whether or not the photometric value thus obtained is suitable for use in exposure control (step
76). This is to determine, for example, whether the obtained integrated data can be used as a photometric value for one horizontal line. When the luminance signal Y _L is saturated in the portion of the horizontal scanning line which is the object of photometry, the integrated data is not suitable for use as a photometric value. The upper limit of this predetermined range is determined in consideration of the dynamic range of the CCD 4, the gain of the GCA 9 and the amplifier circuit 18, and the like so that the integrated data based on the saturated luminance signal Y _L can be excluded. On the other hand, even when such a portion is extremely dark in the horizontal scanning line which is the object of photometry and the luminance signal Y _L is almost due to the noise component, it is not appropriate to use the integrated data as the photometric value. Therefore, the lower limit value of the above-mentioned predetermined range is set to the level at which the integrated data in which the noise component is dominant is excluded. It is also preferably determined whether the photometric value is within the range corresponding to the exposure condition set in step 71.

When it is determined that the obtained photometric value is suitable for use in exposure control, it is then determined whether or not focus control is possible based on the obtained photometric value (step 80). . In this case, since the photometric value is calculated based on the video signal output from the CCD 4, it is determined whether or not the focus control can be performed in consideration of the shutter speed and the aperture value. In addition, whether or not focus control is possible may be determined based on the photometric information obtained from the photometric element 26.

Even if the subject is suitable for the exposure control, it may be inappropriate because it takes too much time to be used for the focus control because the subject has low brightness. In this case, the preflash is set by the strobe device to control the focusing of the imaging lens 4 (step 81), and the flag is set to 1 (step 82).

Next, the exposure condition (aperture value, shutter speed) is set based on the photometric value, and the aperture value and the shutter speed of the aperture are set so as to meet these exposure conditions (step 83). However, in this case, since the subject is considered to have low brightness, stroboscopic light is often emitted in actual shooting, so it may be considered that the exposure conditions are set to correspond to stroboscopic light emission.

Then, at time t ₂ , the changeover switch 13
Is switched to the input terminal S3 side (step 84). Figure 8
As shown in FIG. 8B, a part of the period from time t _{2 to} t ₅ is shown, and as shown in FIG. 8B, the X-on signal is at H level and the stop signal is at L level. During this period, strobe light is emitted and a video signal is read from the CCD 4. As a result, the integration of the video signal and the A / D of the integrated signal are performed on the horizontal scanning line in the ranging area as described above.
The addition of the converted and A / D converted integral data is performed over the entire focus detection area (steps 85 and 90).

Since the electric charge accumulated in the main capacitor 43 is discharged, even if the discharge tube 45 emits light for the same time, the amount of emitted light does not become constant. Therefore, the light emission time is controlled so as to gradually increase, and the light emission amount is always constant.

If focus control is possible based on the photometric value (YES in step 80), the flag is set to 0 (step 86).

Next, the exposure condition is set based on the photometric value, and the aperture value of the diaphragm and the shutter speed are set so as to satisfy this exposure condition (step 87). Further, the changeover switch 13 is changed over to the input terminal S3 side (step 8
8), distance measurement processing similar to step 85 is performed (step 89). However, at this time, pre-flashing is not performed.

As described above, the distance measurement addition data is collected while feeding out the image pickup lens 3 by 10 μm for each frame (B field). A counter is provided to count the number of times the imaging lens 3 is extended.

When the addition data is obtained for the distance measuring area, the counter is incremented (step 91) and the image pickup lens 3 is extended by 10 μm (step 92). The obtained addition data is stored in the memory area shown in FIG.

If the counter value does not exceed 5, the flag is checked (step 94), and if the flag is 1, step 8
The processes of 5, 90 to 94 are repeated, and if the flag is 0, the processes of steps 89, 90 to 94 are repeated.

When the counter value exceeds 5, the six pieces of focus detection addition data in the area shown in FIG. 6 are compared with each other to obtain the maximum value (step 87). Then, the image pickup lens is placed at the position corresponding to the maximum addition data for focus detection.
24 is displaced and positioned there. In the example shown in FIG. 7, the imaging lens 24 is positioned at a position extended by 30 μm from the initial position.

[0080] As described above, the photometry and focusing control is performed setting and focusing of the terminated exposure conditions, and the changeover switch 13 is switched to the input terminal S1, t from time t ₆
Within the period of ₇ , move to the main shooting. When the subject has low brightness, the X-on signal becomes H level and the stop signal becomes L level as shown in FIG. 8A, and the main photographing is performed under the strobe light emission.

If it is determined in step 76 that the photometric value is in an inappropriate range, the exposure condition is changed (step 77). The exposure amount is reduced when the photometric value is small, and is increased in the opposite case.

In the above-described embodiment, when the subject cannot be controlled in focus due to low brightness, the strobe device performs pre-light emission to perform focus control. However, an auxiliary light source such as a light emitting diode may be used instead of the strobe device. . For example, a red light emitting diode is used as this light emitting diode. In this case, it is preferable to use a red light emitting diode having a wavelength equal to the red wavelength of the color filter provided in the CCD 4. As a result, the reflected light of the red light emitting diode is synchronized with the red video signal, so that color unevenness of the image can be prevented.

Further, photometry is performed based on the video signal output from the CCD 4, and it is determined whether or not the preflash is emitted by the strobe device. The so-called external AE sensor is used to determine the preflash by the strobe device. May be.

Further, in the above description, steps 74 to 79 in FIG.
However, the exposure amount may be immediately determined based on the preliminary photometry.

[Brief description of drawings]

FIG. 1 is a block diagram of a digital still camera according to an embodiment of the present invention.
It is a block diagram which shows the electric constitution of a video camera.

FIG. 2 is a diagram showing a photometric area set within a shooting area.

FIG. 3 is a time chart showing photometric processing.

FIG. 4 is a diagram showing a distance measuring area set within a photographing area.

FIG. 5 is a time chart showing distance measurement processing.

FIG. 6 is a diagram showing a storage area of addition data for focus detection.

FIG. 7 is a graph showing focus detection addition data.

8A and 8B are time charts showing a procedure of processing of exposure control and focusing control.

FIG. 9 is a flowchart showing a procedure of processing of exposure control and focusing control by the CPU.

FIG. 10 is a flowchart showing a procedure of processing of exposure control and focusing control by the CPU.

[Explanation of symbols]

 4 CCD (solid-state electronic image sensor) 5 CPU 19 Gate circuit 20 Band pass filter 21 Detection circuit 22 Integration circuit 23 Amplification circuit 24 Imaging lens 25 Imaging lens driving device 26 Photometric sensor 27 Distance measuring sensor 30 Emission light intensity control circuit 40 Charging Circuit 45 Discharge tube 46 Stop circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Izumi Miyake 3-11-46 Izumi, Asaka-shi, Saitama Fuji Shashin Film Co., Ltd.

Claims (10)

[Claims] 1. A video camera equipped with an imaging lens and an imaging optical system including a solid-state electronic imaging device for converting an optical image incident through the imaging lens into a video signal and outputting the video signal. A high-frequency component for focus detection is extracted from the image signal, and a focus control unit that controls the focus of the imaging lens from the extracted high-frequency component, a photometric unit that measures the subject brightness, and a photometric unit that measure The determination means determines whether the subject brightness level is below a predetermined level at which focusing control by the focusing control means is impossible, an auxiliary light source for projecting auxiliary light on the subject, and the determination means described above. When it is determined that the level is lower than the predetermined level, the auxiliary light source is used to project the auxiliary light onto the subject, and the focusing control means is used to perform the focusing control. Control means video camera, with a controlled such. 2. The auxiliary light source includes a strobe light emitting device and strobe light emitting device control means for controlling the amount of light emitted from the strobe light emitting device to be constant.
The video camera according to claim 1. 3. The video camera according to claim 1, wherein the auxiliary light source is a red light emitting device. 4. The photometric means extracts a component relating to a luminance signal from a video signal output from the solid-state electronic image pickup device, and measures the subject luminance based on the extracted component relating to the luminance signal. The video camera described in 1. 5. The video camera according to claim 1, wherein the photometric means is a photometric element. 6. An image pickup optical system including an image pickup lens, a solid-state electronic image pickup device for converting an optical image incident through the image pickup lens into a video signal and outputting the image signal, and focus detection from a video signal output from the solid-state electronic image pickup device. In the video camera equipped with the focus control means for extracting the high-frequency component for, and controlling the focus of the imaging lens from the extracted high-frequency component, the subject brightness is measured, and the measured subject brightness level is It is determined whether or not the level is below a predetermined level at which focus control processing by the focus control means is impossible, and if it is determined to be below the predetermined level, auxiliary light is projected onto the subject, and the focus control means performs A focusing method for a video camera, which performs a high-frequency component extraction process and the focusing control process based on the extracted high-frequency component. 7. The focusing method for a video camera according to claim 6, wherein the auxiliary light is projected from a strobe light emitting device and is controlled so that the amount of light emitted from the strobe light emitting device is constant. 8. The method of focusing a video camera according to claim 6, wherein the auxiliary light is projected from a red light emitting element. 9. The subject brightness is measured by extracting a component related to a brightness signal from a video signal output from the solid-state electronic image pickup device and measuring the subject brightness based on the extracted component related to the brightness signal. The method of focusing a video camera according to claim 6. 10. The video according to claim 6, wherein the measurement of subject brightness is performed by a photometric element.
How to focus the camera.