JP2691206B2 - Auxiliary lighting device for autofocus cameras - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an auxiliary lighting device for an autofocus camera, and more particularly to a large number of photoelectric elements that receive light from a subject and an analog shift register for transferring accumulated charge. Using a self-scanning image sensor, an integration operation of accumulating electric charges corresponding to the brightness of the subject sequentially output from the large number of photoelectric elements over a predetermined integration time is performed, and an image signal obtained by this operation is arithmetically processed. Thus, the present invention relates to an auxiliary lighting device for focus detection used in an autofocus camera that performs focus detection.

(B) Prior Art Various focus detection mechanisms for autofocus cameras have been proposed to date. Among them, a so-called self-scanning image sensor receives light from a subject and calculates an image signal from the image sensor. Some are configured to perform focus detection by processing. This type has an advantage that focus detection can be performed only with natural light, but has a disadvantage that focus detection cannot be performed when the brightness of the subject is extremely low. Therefore, various proposals have also been made regarding auxiliary illumination for focus detection that maintains the function of focus detection by projecting auxiliary light in such a case.
For example, it is described in JP-A-57-10510, JP-A-60-46514, and JP-A-60-46513, but all of them are necessary for determining whether or not auxiliary lighting should be performed. The problem was that it took a long time. That is, the image sensor receives light from a subject by a large number of photoelectric elements (photodiode arrays) and performs an integration operation of accumulating charges corresponding to the subject brightness from these photoelectric elements. A monitoring photoelectric element is arranged in the vicinity of the photoelectric element to determine the integration time, and a monitor signal, which is a charge (current) corresponding to the subject brightness from the monitoring photoelectric element, passes through a predetermined time constant circuit. The integration time is determined by the time required to discharge to a predetermined voltage. Then, this integration time is counted, and the necessity of auxiliary light is determined based on the magnitude of this count value.

Therefore, the present applicant has attempted a method of determining the necessity / non-necessity of the auxiliary light by detecting the voltage immediately after the integration operation starts, that is, at a time much earlier than the integration time. Since the voltage difference between the immediately preceding monitor signal and the reference voltage changes with the temperature change, a new problem is encountered in that a correct determination cannot be made.

(C) Purpose The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide auxiliary light if the autofocus camera is used in any temperature environment from low temperature to high temperature. It is an object of the present invention to provide an auxiliary illumination device for an autofocus camera that can perform unnecessary determination accurately and quickly, and thus can accurately and quickly perform focus detection.

(D) Configuration In order to achieve the above-mentioned object, the present invention uses a self-scanning image sensor having a large number of photoelectric elements that receive light from a subject and an analog shift register for transferring accumulated charge, and uses the large number of photoelectric cells described above. Used in an autofocus camera that performs focus detection by performing an integration operation of accumulating electric charges corresponding to the brightness of the subject sequentially output from the element over a predetermined integration time, and processing an image signal obtained by this operation. In an auxiliary lighting device for focus detection, brightness monitoring means for detecting the brightness of the subject and outputting a monitor signal corresponding thereto, reference voltage generating means for outputting a predetermined reference voltage, and focus detection for the subject Auxiliary light projecting means for projecting the auxiliary light and the brightness of the above-mentioned subject for performing exposure control and the like and outputting photometric data corresponding thereto The photometric means, which receives the monitor signal and the reference voltage, starts the integration operation, and when a predetermined time sufficiently shorter than the integration time has elapsed, the monitor signal and the reference voltage are compared in magnitude. Comparing means for outputting a large / small signal corresponding to a large / small relationship, and a light emitting judging means for receiving the large / small signal and the photometric data and judging whether or not the auxiliary light is projected by a combination thereof, It is characterized in that the auxiliary light is projected from the auxiliary light projecting means on the basis of the determination result of the light projecting determination means.

Hereinafter, an embodiment of the present invention will be specifically described with reference to the accompanying drawings.

FIG. 1 is a block diagram showing the overall configuration of an auxiliary lighting device for an autofocus camera according to the present invention.

In FIG. 1, 1 is a monitor circuit that receives light from a subject and outputs monitor signals (MS1) and (MS2), and an image signal (OS) that also includes a luminance signal that receives light from the subject and that corresponds to subject brightness. The photoelectric conversion unit includes a self-scanning image sensor (hereinafter abbreviated as “CCD”) that outputs a compensation output (DOS) that serves as a reference for the black level of the image signal (OS).

2 is an average value circuit that receives the monitor signals (MS1) and (MS2) and outputs a monitor signal (MS0) that is the average value of these, 3 is the compensation output (DOS), and a slightly lower reference A reference voltage generation circuit as a reference voltage generation unit that outputs a voltage (VS).

4 has a reference voltage Vt internally, and the monitor signal (MS
0) to compare the reference voltage Vt and monitor signal (MS0)
When becomes smaller, the integration end signal (IE) is output, and at the same time, the image signal (OS) and the compensation output (DOS) are received to perform a pre-processing to extract only the brightness component of the subject, and the processed output signal ( It is an image signal processing circuit that outputs as (OUT).

5 is the basic clock (φ) and start signal (STR)
Is a microcomputer that outputs (hereinafter abbreviated as "CPU"). Reference numeral 6 is an A / D converter as an analog / digital converting means built in the CPU 5, which receives a processing output signal (OUT) and image data (D) which is a digital signal.
Is output. Reference numeral 7 denotes a distance measuring calculation unit which is provided in the CPU 5 and receives the integration end signal (IE) and the image data (D) to calculate the distance to the object, and 8 denotes the distance measuring operation from the distance measuring calculation unit 7. A lens control unit that receives data (AF) and drives a photographic lens (not shown) to perform focus adjustment, that is, focus matching with respect to the subject.

9 is the reference voltage (VS) and the monitor signal (MS
0), the monitor signal (MS0) is higher than the reference voltage (VS) to the L level, which indicates that the subject brightness is low, and the monitor signal (MS0) is low, to the H level, which indicates that the subject brightness is high. , A comparator as a comparison means for inverting the signal level of a bright / dark signal (NL) as a large / small signal.

10 measures the brightness of the subject for automatic exposure control etc.,
Metering unit that outputs metering data (AE) corresponding to this, 11
Is provided in the CPU5, receives the light / dark signal (NL) and the photometric data (AE), and the photometric data (AE) is LV
The judgment result of 6 or more and LV4 or less and the light / dark signal (N
L) is a light emission determination unit that determines whether or not auxiliary light is necessary based on a combination of L level and H level, and outputs the result as a control signal (C).

Reference numeral 12 denotes a light projecting unit as a auxiliary light projecting unit that receives the control signal (C) and projects auxiliary light for focus detection onto a subject.

13 is a timing control circuit, which is the integration end signal (IE)
Receiving initial setting pulse (ST), shift pulse (SH) and integral clear gate pulse (ICG) to photoelectric conversion unit 1 and dividing the basic clock (φ) from CPU5 to clock (φ1) , (Φ2) are output to the photoelectric conversion unit 1.

The CPU 5 has a timer TM inside, and the timer TM is set to about 1/10 of the average integration time. Hereinafter, this time will be referred to as "monitor detection time".

Further, the timing control circuit 13 uses the integration end signal (IE)
In response to this, the integrated clear gate pulse (ICG) is output, the start signal (STR) is received, and the initial setting pulse (ST) is output. ) Let me.

FIG. 2 is a block diagram showing the configuration of the photoelectric conversion unit 1.

In FIG. 2, 14 is the CCD, and 15 and 16 are the monitor photodiodes which together constitute the monitor circuit. In the CCD 14, 17 is a photodiode array composed of a large number of photoelectric elements that receive light from a subject, 18 is a barrier gate for accumulating photocurrent corresponding to each pixel flowing in the photodiode array 17, 19 is an integration clear gate,
20 is a storage electrode, 21 is a CC as an analog shift register
In the D shift register, the charges accumulated in the barrier gate 18 are transferred to the accumulation electrode 20 via the integration clear gate 19, and further transferred to the CCD shift register 21. Two
Input terminals 2 and 23 are connected to the shift register 21 and receive the clock pulses (φ1) and (φ2), respectively.
4, 25 and 26 are the initial setting pulse (ST), shift pulse (SH) and integral clear gate pulse (IC
G) is an input terminal for receiving.

An image signal output circuit 27 is connected to the output terminal and the input terminal 22 of the shift register 21 and outputs the image signal (OS) consisting of a time series in which the luminance signal is reset at each clock (φ1) cycle. , 28 are connected to the input terminal 24 and are charged to a predetermined voltage which becomes a reference of the black level when receiving the initial setting pulse (ST), and output the compensation output (DOS) holding this voltage substantially constant. It is a compensation output circuit.

Described below is the configuration of the monitor circuit. Reference numerals 29 and 30 are monitor photodiodes in which the monitor photodiodes 15 and 16 arranged in the vicinity of the photodiode array 17 are shown as specific circuit elements, and the anode side is It is grounded. 31 and 32 are field effect transistors whose drain side is connected to the cathode side of the monitoring photodiodes 29 and 30, respectively, and whose gates are grounded (hereinafter abbreviated as “FET”, not limited to these FETs 31 and 32,
Similar items are referred to as “FET”. ), 33 and 34 have one end grounded and the other end connected to the source side of the FETs 31 and 32, and 35 and 36, the source side connected to a power source + V having a predetermined voltage, and the drain side connected to the capacitor 33 and FETs, 37 and 3 connected to the other end of 34 and each gate connected to input terminal 24.
8 is a buffer amplifier whose input terminals are connected to the drain sides of the FETs 35 and 36, and 39 and 40 are outputs which are connected to the output terminals of the buffer amplifiers 37 and 38 and output monitor signals (MS1) and (MS2), respectively. It is a terminal. Incidentally, 41 and 42 are monitor circuits as the brightness monitoring means configured in this way.

The monitor photodiodes 29 and 30 are affected by temperature within the monitor detection time and generate a large drift in a range far from room temperature, for example, close to −15 ° C. or close to + 40 ° C. It has characteristics. However, at room temperature, the drift is almost zero.

3 and 4 are timing charts for explaining the operation of the main part of the present invention.

In FIG. 3, V1 is the voltage of the compensation output (DOS), T
1 is the monitor detection time and T2 is the integration time. However, T1 ≒ T2 / 10 is not established for the convenience of drawing.

FIG. 5 is a diagram showing the operation results of FIG. 1 classified.

In Fig. 5, LV6 and LV shown as photometric data (AE)
4 has the following meaning. That is, the distance measurement calculation unit 7 shown in FIG. 1 has the ability to prevent the presence or absence of auxiliary light from affecting the distance measurement data (AE) when the brightness of the subject is in the region of LV6 to LV4. In the area above LV6, there should be no supplementary light, and conversely, in the area below LV4, correct ranging cannot be performed without supplemental light.

FIG. 6 is a flowchart showing the operation sequence of the light emission determination unit 11.

Next, the operation of the present embodiment configured as described above will be described. Prior to the description of the main part, the photoelectric conversion unit 1 shown in FIG.
The operation of will be described briefly.

When the initial setting pulse (ST) is input to the input terminal 24,
The charges accumulated in each pixel of the photodiode array 17 and the barrier gate 18 are transferred to the storage electrode 20, the FETs 35 and 36 are turned on, and the capacitors 33 and 34 are compensated output (DOS) by the power supply voltage + V. It is charged to voltage V1.
The above operation is called an initial setting operation.

Next, when the initial setting pulse (ST) disappears, the voltages of the capacitors 33 and 34 are output as monitor signals (MS1) and (MS2) via the buffer amplifiers 37 and 38. That is, since the photocurrent flowing through the monitor photodiodes 29 and 30 increases or decreases according to the brightness of the subject, the monitor signal (MS1),
The voltage drop speed of (MS2) corresponds to the brightness of the subject. The photodiode array 17 receives light from a subject and a photocurrent flows. This photocurrent is stored in each pixel and corresponding barrier gate 18. When the integration is completed and the integration completion signal (IE) inputs the integration clear gate pulse (ICG) to the input terminal 26, the excess charge accumulated in the storage electrode 20 is cleared.

Now, after this, when the initial setting pulse (ST) is input again, the above initializing operation is executed, and the charge of the storage electrode 20 is transferred to the CCD shift register 21 by the shift pulse (SH). The CCD shift register 21 sequentially transfers the charges by the clocks (φ1) and (2φ), and the voltage is output as an image signal (OS) via the buffer amplifier 27.

Next, the operation of the image signal processing circuit shown in FIG. 1, particularly preprocessing, will be briefly described. The image signal (OS) output from the CCD 14 of the photoelectric conversion unit 1 that receives light from the subject and the reference signal is used. The image signal processing circuit 4 receiving the compensation output (DOS) substantially removes the clock pulse superimposed on the image signal (OS) as a noise component, and then performs processing such as compression of the signal variation range. Output as output signal (OUT).

Now, the operation of the main part will be described. First, as shown in FIG. 3, the case where auxiliary light is required will be described.

By operating a distance measuring switch or a release switch (not shown), the CPU 5 detects this and outputs a start signal (STR). This time is t1 in FIG.
Timing control circuit 1 that received the start signal (STR)
The output from 3 triggers the CCD 14 initialization operation. Further, the CPU 5 starts the time counting operation of the timer TM from the time point t1. The monitor outputs (MS1) and (MS2) become the monitor signal (MS0) via the average value circuit 2, and this monitor signal (MS0)
0) begins to fall. At time t3 when the timer TM measures the monitor detection time T1, the light emission determination unit 11 in the CPU 5 checks the light / dark signal (NL). At time t3, the monitor signal (MS
Since 0) is higher than the reference voltage (Vs), the light / dark signal (NL) remains at L level.

On the other hand, the photometry data (AE) from the photometry unit 10 is received by the light emission determination unit 11 at the same time t3, and the flowchart of FIG. 6 starts from START at the time t3.

Since the first conditional branch "Monitor signal is large?" Is (MS0)> Vs as described above, the flow branches to YES. Here, if the photometric data (AE) is LV5, the next conditional branch "LV6 or higher?" Is branched to NO, and at the next "forced flash", the emission determination unit 11 notifies the CPU5 to that effect. Then, the light emission determination unit 11 is informed that it is time to emit light. In response to this, the light projecting determination unit 11 causes the light projecting unit 12 to project the auxiliary light with the control signal (C).

After that, at time t4 when time T2 elapses, the monitor signal (MS
0) reaches the reference voltage Vt, and at this time point t4, the image signal processing circuit 4 outputs the integration end signal (IE) and receives it.
The CPU 5 notifies the A / D converter 6 and the distance measurement calculation unit 7 to start the operation, and also notifies the light emission determination unit 11 that it is time to stop the light emission, and the light emission determination unit 11 sends a control signal (C). The light emitting unit 12 stops the light emission, and the A / D converter 6
Starts converting the processed output signal (OUT) into image data (D) one after another, and upon receipt of this, the distance measurement calculation unit 7 calculates the in-focus position, outputs distance measurement data (AF), and receives this. The lens control unit 8 drives the projection lens to the in-focus position to complete the focus detection operation. The above-mentioned operation is called an emission focus detection operation.

Next, the non-emission focus detection operation without light emission will be described with reference to FIGS. 4 and 6.

At time t5, the monitor signal (MS0) is charged to the voltage V1 of the compensation output (DOS) and starts discharging at time t6. Since the subject is sufficiently bright, the monitor signal (MS0) drops rapidly, falls below the reference voltage Vs at a time point ta before measuring the monitor detection time T1, and the bright / dark signal (NL) is inverted to the H level.
At the time t7 when the monitor detection time T1 has elapsed, the emission determination unit 11
Check the light-dark signal (NL) and photometric data (AE). Now, turning to FIG. 6, since “MS0” <Vs is displayed for “Are the monitor signals large?”, Branch to NO, and the photometric data (AE)
Is LV5, the next “LV4 or less?” Is branched to NO, and the next “non-light emission” causes the light emission determination unit 11 to output the control signal (C).
Is not output, the light emitting unit 12 does nothing. That is, the auxiliary light is not emitted. And when the integration time T2 has passed
At t8, the integration end signal (IE) is output and the focus detection operation is performed.

Therefore, as shown in Fig. 5, the photometric data (AE) is LV.
Between 5 and LV6, it is determined that light is emitted based on the state of the light / dark signal (NL), and is not emitted based on The light is forcibly turned off regardless of the state of, and conversely, when the photometric data (AE) is LV4 or less as indicated by and, the light is forcibly emitted regardless of the state of the light-dark signal (NL).

In other words, in a room temperature environment, monitor signal (MS0)
When the reliability of LV4 to LV6 is high, the area inside LV4 to LV6 is judged more finely. The consumption is reduced, and at LV4 and below, the light is forcibly emitted to prevent erroneous ranging due to the subject being too dark.

As described above, according to the present embodiment, even if the ambient temperature is greatly deviated from the normal temperature to the high temperature side or the low temperature side, the auxiliary light emits light at the subject brightness that does not require the auxiliary light. Therefore, there is an advantage that the accuracy of focus detection is not affected by the subject brightness.

When the ambient temperature is room temperature, the photometric data (AE)
Within the range of LV4 to LV6, it is possible to finely determine whether or not the auxiliary light is necessary by the monitor signal (MS0), which has the advantage of further improving the accuracy of focus detection.

Further, since it is determined whether or not the auxiliary light is necessary during one integration period, there is an advantage that the time for focus detection is much shorter than in the conventional case. The monitor detection time T1 is approximately 1/10 of the integration time T2, and the auxiliary light is turned on for the remaining 9/10, so the amount of auxiliary light should be kept during the entire integration period. Compared to, it doesn't have to be that much.

It should be noted that the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention.

For example, LV6 and LV4 in FIGS. 5 and 6 are not limited to this value, and may be increased or decreased to some extent depending on the capability of the distance measurement calculation unit 9.

Further, the monitor detection time T1 is not limited to about 1/10 of the integration time T2, and may be changed in a small amount as the constants of the monitor circuits 41 and 42 change.

Further, although the integration end signal IE is explained as being directly received by the CPU 5, depending on the timing relationship of the circuits of the respective parts, it may be passed through the timing control circuit 13 shown in FIG. 1 (shown by the broken line).
It may be configured to receive it.

(E) Effect As described above in detail, according to the present invention, the brightness for detecting the brightness of the subject after a predetermined time sufficiently shorter than the integration time of the self-scanning image sensor that receives light from the subject has elapsed. The magnitude relationship between the monitor signal from the monitoring means and the predetermined reference voltage is compared, and the presence / absence of auxiliary light is determined by the combination of the magnitude signal corresponding to the magnitude relationship and the photometric data from the photometric means, and the remaining Since the auxiliary light is turned on and off during the integration period of, the focus can be detected by one integration, and even if the reliability of the large and small signals is lowered, it is inappropriate due to the combination with the photometric data. It is possible to provide an auxiliary light illuminating device for an automatic focusing camera, which can prevent light emission of various auxiliary lights and can perform quick and accurate focus detection.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the overall configuration of an auxiliary light illuminating device for an autofocus camera according to the present invention, and FIG. 2 is a block diagram showing the configuration of the photoelectric conversion unit of the embodiment shown in FIG. Three
FIGS. 4 and 5 are timing charts for explaining the operation of the main part of the present invention, FIG. 5 is a diagram showing the operation results of FIG. 1 in a classified manner, and FIG. 6 is the main part of the present invention. It is a flow chart which shows the operation sequence of the light emission judgment part. 1 ... Photoelectric conversion unit, 2 ... Average value circuit, 3 ... Reference voltage generation circuit, 4 ... Image signal processing circuit, 5 ... Microcomputer (CPU), 6 ... A / D converter, 7 ... Distance measuring unit, 8 ... Lens control unit, 9 ... Comparator, 10 ... Metering unit, 11 ... Emitting judgment unit, 12 ... Emitting unit, 13 ... Timing control circuit, 14 ... Image sensor , 15,16,29,30 …… Monitor photodiode, 27 …… Image output circuit, 28 …… Compensation output circuit, 31,32, 35, 36 …… Field effect transistor, 33, 34 …… Capacitor, 37 , 38 …… Buffer amplifier, 41,42 …… Monitor circuit.

Claims (1)

(57) [Claims] 1. Using a self-scanning image sensor having a large number of photoelectric elements for receiving light from an object and an analog shift register for transferring accumulated charges, and corresponding to the luminance of the object sequentially output from the large number of photoelectric elements. In the auxiliary illumination device for focus detection used in an autofocus camera that performs focus detection by performing an integration operation of accumulating the accumulated charges for a predetermined integration time and performing an arithmetic processing of an image signal obtained by this operation, Luminance monitoring means for detecting luminance and outputting a monitor signal corresponding to the luminance,
Reference voltage generating means for outputting a predetermined reference voltage, auxiliary light projecting means for projecting auxiliary light for focus detection on the object, and brightness of the object for exposure control and the like, and corresponding thereto The photometric means for outputting the measured photometric data, the monitor signal and the reference voltage, and a predetermined time sufficiently shorter than the integration time since the integration operation is started. Comparing means for comparing the relationships and outputting a large / small signal corresponding to the large / small relationship; and a light emitting judging means for receiving the large / small signal and the photometric data and judging whether or not the auxiliary light is projected by a combination thereof. And an auxiliary illumination device for an automatic focusing camera, characterized in that the auxiliary light is emitted from the auxiliary light projecting means based on the determination result of the light emission determining means.