JPH045361B2 - - Google Patents

Description

Detailed Description of the Invention [Technical Field] The present invention relates to an automatic focus adjustment device, and more specifically, the present invention relates to an automatic focus adjustment device, and more specifically, an automatic focus adjustment device that detects the amount of shift in the focal position of an optical system as a difference between output signals of two systems of light receiving means. The present invention relates to an automatic focusing device that moves an optical system according to a positional shift of a focal point, and stops moving the optical system when the difference between the signals is within a predetermined focusing range.

[Prior Art] In recent years, automation of operations in various photographic devices has progressed, and in particular, various systems have been proposed for automatic focus adjustment devices. A system as shown in FIG. 1 is known as one of the conventional active automatic focusing mechanisms.

In FIG. 1, the reference numeral L0 is a mirror for photographing a camera, which is moved along the optical axis O-O' by a driving means such as a motor. Mirror copper L
Two lenses L1 and L2 are arranged on both sides of the lens 0, and a light source I and a photodiode DA and a photodiode DB are provided behind them, respectively. Photodiode DA,
The DB is moved in a direction substantially perpendicular to the optical axis O-O' in conjunction with the movement of the mirror L0.

In the above configuration, automatic focus adjustment is performed as follows.

The light from the light source I is irradiated onto the object Z on the optical axis O-O' through the lens L1, and the reflected light is transmitted through the lens L2 to two photodiodes DA,
Guided on DB. Since the light from the light source I is emitted at a constant irradiation angle, the position of the reflected light from the subject Z in the direction perpendicular to the optical axis O-O' at the photodiode position changes depending on the distance to the subject Z. Therefore, the interlocking of the mirror copper L0 and the two photodiodes is adjusted so that when the mirror copper L0 focuses on the subject, the same amount of reflected light returns onto the two photodiodes DA and DB. If you do so, you can automatically adjust the focus by checking the outputs of the photodiodes DA and DB.

The conventional active automatic focus adjustment mechanism described above reduces the amount of reflected light detected by the photodiode when the subject is far away or when a light source that disturbs the signal light of light source I is in front of the camera.
The drawback is that the signal-to-noise ratio deteriorates, making it impossible to perform normal focus adjustment.

If the SN ratio is poor, the mirror may move due to external light, even though the in-focus state has been established and the camera or subject has not changed its position.
There were cases where the image was out of focus or the size of the image changed, making it unsightly.

Furthermore, many of the conventional automatic focusing devices as described above are configured to measure the amount of light received by a photodiode using an integral method. FIG. 2 shows changes in the integral value over time when the amount of received light is measured using the integral method. In such a device, the integral value is reset every measurement period formed when the integral value of one photodiode reaches a predetermined value, and the same measurement cycle is sequentially repeated. During this measurement operation, the light source I is constantly emitting light as shown in the figure. Keeping the light source emitting light all the time in this way leads to an increase in power consumption,
In portable devices such as cameras, it is inevitable that the power supply section will be large, which is very disadvantageous.

[Purpose] The present invention has been made in view of the above points, and it is possible to reliably perform automatic focus adjustment even when there is ambient light or when the subject is relatively far away, and the power consumption of the light emitting unit is small. It is an object of the present invention to provide an automatic focus adjustment device that is easy to use.

[Example] Hereinafter, the present invention will be described in detail based on an example shown in the drawings. However, among the configurations described below, the interlocking mechanism of the camera mirror L0 and the photodiodes DA and DB for detecting reflected light is explained in the first section.
The configuration is similar to that shown in the conventional example in the figure.

FIG. 3 shows the circuit configuration of the automatic focusing device of the present invention, and in the same figure, reference numerals DA and DB indicate photodiodes arranged in parallel for detecting reflected light. photodiode
The outputs of DA and DB are amplified by amplifiers 1A and 1B, respectively, and sent to filters 2A and 2B, respectively.

On the other hand, the light source I is driven by the oscillation frequency of the reference oscillator 13 via the light emission control section 14 including a driver. This frequency is selected to be different from the frequency of the commercial power supply that turns on indoor light sources to prevent disturbances.

Therefore, filters 2A and 2B are
It is set to pass only signals in the emission frequency range of . The outputs of the filters 2A and 2B are input to integrators 4A and 4B via switches 3A and 3B, respectively, which are electronically controlled to open and close.

The integrators 4A and 4B are constructed from integrating circuits using well-known operational amplifiers, and their integrating capacitors can be reset by switches 4C and 4D, respectively.

The output voltage VA of integrator 4A is determined by comparator 5.
Input to the + terminals of AH and 5AL. Also,
The output voltage VB of the integrator 4B is the comparator 5BH.
and is input to the + terminal of 5BL.

On the other hand, the - terminal of each comparator is supplied with a threshold voltage obtained by dividing the power supply voltage by resistors R1 to R4 connected in series. Comparator 5AH
The voltage VH at the connection point of the resistors R1 and R2 is supplied to 5BH and 5BH as a threshold voltage. Comparators 5AL and 5BL are supplied with either voltage VL or VL' at the connection point of resistors R2-R3 or R3-R4. This selection is made by switch 3C as described later. These voltages VH, VL, and VL' are determined according to the required focusing accuracy, as will be described later.

The outputs of comparators 5AH and 5BH are connected to the input of OR gate 61. or gate 61
The output of is input to the OR gate 62, and
It is adapted to trigger flip-flops 91 and 92. The output Qn of the counter 12 is input to the other input of the OR gate 62.

The output of the OR gate 62 is adapted to trigger the mono multivibrator MM1. That is, when either comparator 5AH or 5BH becomes high level, a high level pulse is output from OR gates 61 and 62, and this pulse triggers mono multivibrator MM1 and flip-flops 91 and 92.

The output of the mono multivibrator MM1 is input to an inverter 71, a delay circuit DL1 consisting of a similar mono multivibrator, and an OR gate 63. The inverter 71 and the mono-multivibrator MM1 are connected to the block 20 indicated by the broken line.
The input/output to this block 20 is performed through the three connection points A to C shown in the figure.

The output of the inverter 71 is adapted to control the switches 3A, 3B and the light emission control section 14. The switches 3A and 3B are opened by a low level input, and the light emission control section stops the light source I from emitting light by the same low level input.

The outputs of comparators 5AL and 5BL are applied to data inputs of flip-flops 91 and 92, respectively. The outputs of these flip-flops 91 and 92 are connected to a motor control circuit 10.

The motor control circuit 10 includes a flip-flop 91,
The motor 11 that drives the copper mirror L0 is moved in two different directions in accordance with the high level output of the mirror 92. This direction of rotation is adjusted in advance in a direction in which the amounts of light input to the photodiodes DA and DB are equal, depending on the amount of light input to the photodiodes DA and DB.

Also, both outputs of flip-flops 91 and 92 are 2
It is connected to an input AND gate 81, and the output of the AND gate 81 is connected to the control input of the switch 3C. The switch 3C is always connected to the left side of the figure, and is switched to the right side terminal of the figure when the output of the AND gate 81 is at a high level.

On the other hand, the output of the OR gate 63 is connected to the reset terminal of the counter 12. This counter 1
The clock pulse 2 is adapted to step at the falling edge of the output of the reference oscillator 13, and the clock pulse output from the reference oscillator 13 is connected to one input terminal of an AND gate 84. The output of this AND gate 84 is connected to the remaining inputs of the OR gate 63. The output of the counter 12 is connected to the other input of the AND gate 84.

The output Qn of the counter 12 is the flip-flop 9
1,92 and or gate 62
connected to the remaining inputs.

Next, the operation of the above configuration will be explained in detail.

The photodiodes DA and DB output according to the amount of light received, and of this output signal, only the emission frequency component of the light source I is extracted by filters 2A and 2B, respectively, and sent to an integrator 4A via normally closed switches 3A and 3B. , 4B. As shown in FIG. 4, the output voltage of each integrator increases from the start of measurement according to the amount of received light.

Here, the output voltage of the integrators 4A and 4B changes over time t.
Let us consider the case where the values increase as indicated by the symbols VA and VB'.

In this case, since the amount of light received on the photodiode DA side is large, the integrated voltage VA first reaches the threshold value VH of the comparator 5AH at time T. As a result, the comparator 5AH is inverted, the OR gate 61 outputs a high level, and the flip-flops 91 and 92 are triggered. At this time, the data input of the flip-flop 91 has a voltage VA that is already the threshold value of the comparator 5AL, as shown in FIG.
Since it exceeds VL, it is at a high level. Also,
The data input of flip-flop 92 is at a low level since voltage VB' has not yet reached voltage VL at this point.

Therefore, by triggering each flip-flop, flip-flop 91 outputs a high level, and flip-flop 92 outputs a low level.

As a result, the motor control circuit 10 drives the motor 11 to move the mirror and each photodiode so that the amount of light received by the photodiode DB increases. Even when the magnitude of the received light is reversed, the mirror copper is moved in the opposite direction by the same operation.

Further, simultaneously with the triggering of the flip-flops 91 and 92, the mono multivibrator MM1 is also triggered by the output of the OR gate 62. A pulse of a length determined by the connected resistor R9 and capacitor C1 is then applied to the monomultivibrator MM.
Output from 1. This output pulse disconnects the integrators 4A and 4B via the inverter 71, and after the delay time set in the delay circuit DL1 has elapsed,
Switches 4C and 4D are closed via DLI, the integrating capacitor of each integrator is shot, and the integral value is initialized. The counter 12 is also reset via the OR gate 63 by the same pulse.

The output of the mono-multivibrator MM1 is inverted by the inverter 71 and input to the light emission control section 14. Therefore, mono-multivibrator
While the output of MM1 is at a high level, the light source I stops emitting light. When the mono multivibrator MM1 outputs a low level after the time determined by the resistor R5 and the capacitor C1, the light source I is turned on again.
starts to emit light, and a new measurement begins. In other words, after the measurement is completed, the mono-multivibrator MM
The measurement is paused for an output pulse width of 1, and the light emission from the light source I is also stopped during this period.

The counter 12 is used to set the maximum integration time, and if the clock pulses of the reference oscillator 13 have not been reset yet when a certain number of clock pulses of the reference oscillator 13 are counted after the rest period ends and the reset is released as described above, the counter 12 is used to set the maximum integration time. Assuming that the amount of light to be measured cannot be received, a short pulse is generated and applied to the OR gate 62, triggering the mono multivibrator MM1, and performing the same reset operation as described above and stopping the light source from emitting light. At the same time, it resets its own count value via AND gate 84 in synchronization with the clock pulse.

As described above, at the end of each measurement period using the photodiode, the mono multivibrator MM
Since the measurement and the light emitting operation of the light source I are stopped for the time set to 1, power consumption can be reduced by the length of this pause period. Therefore,
It becomes possible to make the power supply unit smaller than before or to extend the life of the power supply battery.

On the other hand, when each integral value increases with signs VA and VB, both comparators 5AL and 5BL have already been inverted when voltage VA reaches voltage VH, so the outputs of flip-flops 91 and 92 are both high. become the level. As a result, the motor control circuit 10 and the motor 11 are stopped, and the movement of the copper mirror is stopped. Therefore, the photodiode
When the output integral value of either DA or DB reaches voltage VH and the other integral value exceeds voltage VL, it is determined that focus is achieved.

At this time, if the subject is far away, the reflectance of the subject is poor, or there is a light source that disturbs the signal light, the signal-to-noise ratio of the signal input to the photodiode will deteriorate, resulting in a decrease in the integrated voltage. The error included in becomes large. There may also be a case where one of the integral values falls below the threshold voltage VL, as in the case of symbol VB' in FIG. 4, even though a focused state is formed. In such a case, conventionally it would be determined that the focus was out of focus and the mirror would be moved, which would cause the camera, such as a video camera or single-lens reflex camera, to become out of focus or have a large image even though it was once in focus. It was very unsightly as the color changed.

However, in the present invention, when flip-flops 91 and 92 are both set, both inputs of AND gate 81 go high, so switch 3C is switched to the right side in FIG. even lower threshold
changed to VL′. In other words, the criteria for the in-focus state are expanded. Therefore, in the present invention, once the object is in focus, it is possible to maintain the in-focus state without the mirror moving due to noise even when there is ambient light or when the subject is far away. Of course, the symbols in Figure 4
When one integral value becomes smaller than VL' at the time of flip-flop trigger, such as VB'', the mirror is moved by the same operation as described above, and at this time, the output of AND gate 81 becomes low level. Therefore, the switch 3C is connected to the left side in FIG.

As described above, when focusing, the criteria for determining focus is expanded, malfunctions due to noise can be prevented, accurate automatic focus adjustment can be performed, and stability against disturbances can be ensured. In the above, a measurement circuit in which the integral value increases is illustrated for ease of explanation, but in a measurement circuit in which the integral value is output as a negative voltage, the higher threshold value should be changed. It's okay. Further, the criteria for determining focus is not limited to two types, and a large number of values may be selected depending on the amount of light received by the photodiode.

In addition, in the above, the measurement is ended when the integral value reaches a predetermined value, and then the light emission and measurement are suspended for a certain period of time, but it is more preferable to It is preferable to configure the time interval to be controlled to be constant.

Specifically, the above operation can be realized by replacing block 20 in FIG. 3 with block 20' in FIG. 5. Block 20' in FIG. 5 has connection points A-D, which are connected to connection points A-C in FIG. 3, respectively. A clock output from the reference oscillator 13 is input to the connection point D. Here, the mono multivibrator MM1 is
It has been replaced by SR flip-flop 93,
The reset is performed by the output Qm of the counter 15. At the same time, this output Qm resets its own count value. Therefore, the SR flip-flop 93 is cleared at regular intervals, and the light source I, which had been turned off, is turned on again.

FIG. 6 illustrates an integral operation when using the configuration of FIG. 5. Here, t _nax indicates the longest integration time determined by the counter 12, t
1 is the time determined by the count value of the counter 15.

As shown in the figure, by setting t1> _tnax , measurements can be performed at regular time intervals, and light emission can be paused for at least t1- _tnax during the measurement period.
When the subject is close, or when the subject has good reflectivity and strong reflected light can be obtained,
Since the measurement is completed in a shorter time, it is possible to take a longer time to stop emitting light, which increases the energy saving effect. Furthermore, since the measurement operation is performed at regular intervals, an average focusing operation can be performed.

In other words, in the circuit of FIG. 5, the pause time is determined according to the amount of received light, and as described above, a high energy saving effect and stable focus adjustment operation can be obtained.

Furthermore, different embodiments of the present invention are shown in FIG. 7 and below.

Conventional devices had the drawback that when the subject was far away and a sufficient amount of reflected light could not be obtained, the motor that moved the mirror was driven by noise, but the circuit shown in Figure 7 has improved this drawback. It is something to do. In the circuit diagram of FIG. 7, the same members as those in FIG. 3 are given the same reference numerals, and detailed explanation thereof will be omitted. Further, illustration of the light receiving circuit and the threshold value control circuit is also omitted here.

The circuit in FIG. 7 differs from FIG. 3 in that the control system for the motor 11 is shown in more detail, and the blocks 21 and 2 shown in broken lines are shown in more detail.
2 is added. Light emission stop control is performed by a flip-flop 93 and counter 15 similar to those shown in FIG.

The motor control circuit 10 in the figure is an AND gate 8
2,83. The non-inverting output of flip-flop 91 and the inverting output of flip-flop 92 are input to AND gate 82.
The inverted output of flip-flop 91 is input to AND gate 83. Furthermore, one of the input terminals of each AND gate 82, 83 is connected to a resistor R5, R
6 and switches 3P and 3Q, it can be controlled to zero potential.

In this circuit, both flip-flops 91,
92 is set, that is, when a focus determination is made, one of the input terminals of AND gates 82 and 83 is set to a low level, and motor control circuit 10 stops rotation of motor 11. The motor 11 is rotated in that direction only when only one of the flip-flops is set. Therefore, the motor 11 is driven and controlled by the exclusive OR of the two flip-flops.

The switches 3P and 3Q mentioned above are respectively attached to the closest end and the infinitely far end of the copper mirror, and are used to detect movement of the mirror to the corresponding position. When the mirror reaches the end of the movement range from the nearest to infinite distance, switches 3P to 3Q are closed to stop further movement of the mirror.

The pull-up side of the switch 3Q attached to the infinite far end is input to the AND gate 85 of the block 21, the inverter 73, and the AND gate 88 of the block 22.

The output Qn of the counter 12 is connected to the remaining inputs of the AND gate 85 of the block 21.
The output of inverter 73 is connected to one input of AND gate 86 and is also input to AND gate 87 of block 22. and gate 8
The output Q1 of the counter 12 is connected to the remaining input of the counter 6. Here, it is assumed that the output Q1 has a smaller number of measurements than Qn. and gate 85,8
The OR gate 64 resets the counter 12 through the AND gate 84 and the OR gate 63 as in FIG.
2, a flip-flop 93 is set.

On the other hand, block 22 has a similar structure, and inverter 73 is activated by operating switch 3Q.
The two outputs Qm and Qh of the counter 15 are selected via. Here, switch 3
By turning on Q, the output Qh with the longer measurement time is selected.

However, let Qm>Qn.

In the above configuration, when the mirror moves to the infinite end and the switch 3Q is turned on, the AND gates 85 and 88 are closed and the AND gates 86 and 87 are opened. As a result, the output Q1 of the counter 12 and the output Qh of the counter 15 become the normal output Qn, respectively.
It will be used instead of Qm.

Therefore, the mirror copper is at the infinite end and switch 3
While Q is on, the maximum integration time is short,
Integration and light emission pause periods are lengthened. As a result, the flip-flops 91 and 92 are caused by noise components.
This prevents malfunctions in which the mirror is moved due to triggering, and reduces the probability of malfunctions occurring per unit time by shortening the maximum integration time and extending the light emission pause period. At the same time, by shortening the measurement period and extending the light emission pause, the energy saving effect can be further enhanced in areas close to the distance measurement limit.

As described above, reliable and stable focus adjustment can be achieved with lower power consumption.

In the embodiment shown in FIG. 7, the length of the measurement pause period is determined by the counter 15 and gates 65, 87, and 88, but even in the configuration in which the measurement pause period is determined by a mono-multivibrator as shown in FIG. The invention can be implemented in a similar manner. FIG. 8 shows an embodiment configured in this manner.

In FIG. 8, the length of the measurement pause period is determined by the monomultivibrator MM1 as in the case of FIG. 3, but the time constant of this circuit is determined by the resistors R7 and R8.
and capacitor C1. Resistance R
7 and R8 can be connected to the power supply voltage via switch 3D. This switch 3D is controlled by the terminal voltage of switch 3Q. Since the other configurations are the same as those in FIG. 7, their explanation will be omitted.

According to the above configuration, when the optical system moves to the infinite end, the switch 3Q closes, thereby opening the switch 3D. As a result, the pulse width of mono-multivibrator MM1, which was previously determined by resistor R8 and capacitor C1, is changed to resistor R7.
+R8 and capacitor C1, and a longer pulse is output.

In this way, the measurement pause period is lengthened by moving the optical system to the infinite end. Further, at this time, the maximum integration time specified by the counter 12 is shortened in the same manner as in FIG. 7, and the same effect as described above can be obtained.

[Effect] As is clear from the above description, according to the present invention, the amount of deviation in the focal position of the optical system is measured as the difference between the output signals of the two systems of light receiving means, and an integrator that integrates the output signals of the two systems of light receiving means, respectively; , comprising means for initializing the integrator, means for continuing the initialization of the integrator for a predetermined period of time, and means for detecting movement of the optical system toward an infinite end, and after the start of measurement, any of the integrators is When the difference between the output signals of both integrators is within a predetermined range when the signal reaches a predetermined integral value, the movement of the optical system is stopped as in-focus; When the value is outside the predetermined range, a measurement period in which the optical system is moved according to the positional shift of the focal point and a measurement pause period in which both the integrators are initialized for a predetermined time are alternately repeated; , when a movement of the optical system to the infinity end is detected, the maximum time of the measurement period is shortened compared to when the optical system is at other positions. In other words, in areas near the distance measurement limit where the subject is moving far away and cannot receive enough light for distance measurement, the probability of malfunctions due to noise can be reduced. On the other hand, it is possible to provide an automatic focusing device that can achieve low power consumption by shortening the measurement processing period, has excellent ranging reliability, and has low power consumption.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the principle of an active type automatic focusing device, FIG. 2 is a diagram explaining the operation of a conventional automatic focusing device, and FIG. 3 is a diagram showing the configuration of an automatic focusing circuit of the present invention. 4 is a diagram explaining the operation of the circuit in FIG. 3, and FIG. 5 is a diagram explaining the operation of the circuit in FIG.
6 is a diagram showing the operation of the circuit in FIG. 5, FIG. 7 is a circuit diagram showing a further different embodiment of the present invention, and FIG. FIG. 3 is a circuit diagram showing a different embodiment of the present invention. 1A, 1B...Amplifier, 2A, 2B...Filter, 3A, 3B, 3P, 3Q...Switch, 4
A, 4B...Integrator, 5AH, 5BH, 5AL, 5
BL...Comparator, 10...Motor control circuit,
11...Motor, 12, 15...Counter, 13
... Reference oscillator, 14 ... Light emission control section, 61-6
5...OR gate, 81-88...AND gate, 91-93...flip-flop, I...light source, DA, DB...photodiode, MM1...
...Mono multi vibrator.

Claims (1)

[Claims] 1. The amount of deviation in the focal position of the optical system is measured as the difference between the output signals of two systems of light receiving means, and the optical system is moved according to the measured deviation in the focal position, so that the amount of deviation in the focal position of the optical system is determined by An automatic focusing device that stops moving the optical system when the difference is within a predetermined focusing range, comprising: an integrator that integrates output signals of the two systems of light receiving means, and means for initializing the integrator; A means for continuing the initialization of the integrator for a predetermined period of time, and a means for detecting movement of the optical system to an infinite end; When the difference value between the output signals of both integrators is within a predetermined range, the optical system is determined to be in focus and the movement of the optical system is stopped. On the other hand, when the difference value between the output signals of both integrators is outside the predetermined range, the focus is determined to be in focus. A measurement period in which the optical system is moved in accordance with the positional deviation of An automatic focusing device characterized in that when detected, the maximum time of the measurement period is made shorter than when the optical system is in another position. 2. The automatic focus adjustment device according to claim 1, wherein a measurement pause period for each measurement period is extended by detecting movement of the optical system toward an infinity end. 3. The automatic focus adjustment device according to claim 1 or 2, further comprising means for controlling the time interval between the starting points of the measurement period to be always constant. 4. The automatic focus adjustment device according to any one of claims 1 to 3, characterized in that during the measurement suspension period, driving of the light receiving system is stopped.