JPS6251451B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an autofocus camera, and more particularly to an improvement in a light beam projection type distance measuring device using the principle of triangulation.

Prior Art Conventionally, as a distance measuring device used for this type of autofocus, a light beam projecting means is constituted by a light source 1 using a light emitting diode and a projecting lens 2, as shown in the principle configuration in Fig. 1, during distance measuring. A light beam is emitted by a switch operation in , and an imaging lens 4 is provided at a position separated from the optical axis 3 of the projection lens 2 by a base length d, and the imaging surface of the lens has a base length direction. a plurality of photodiodes 5,
These photodiodes 5, 6, 7, 8 are located at each point 9, 10, 1 on the optical axis 3.
1 and 12, respectively, and the distance is detected by detecting which photodiode the reflected light from the object to be measured on the optical axis 3 by the projection of the light beam enters. In this device, if the reflected light of the light beam is not detected by any of the photodiodes, the object to be measured is determined to be in a distance range equivalent to "infinity". It is becoming more and more common. Therefore, with this device, even though the object to be measured is located in a short distance area, such as indoors, before the ``infinity'' area, the reflected light of the light beam is small due to the low reflectance of the object. It may not be detected, and an unfavorable judgment may be made that is contrary to the actual situation of "infinity".

OBJECT OF THE INVENTION An object of the present invention is to use an autofocus camera to perform measurement when it detects that ripples are included in the light from the object to be measured even when the reflected light of the light beam from the object is not detected. The purpose is to specify a specific distance as a distance output.

Features of the Invention In other words, the present invention “has a light projecting lens 2,
Light beam projection means 1, 2, 59, 6 that reflects the light beam toward the object to be measured via this projection lens.
0, and position detection means 5 to 8, which are arranged at a position separated from the optical axis of the light beam by a certain base line length and detect the position where the light beam reflected from the object to be measured is received.
10 to 13, 15 to 18, 21 to 24, distance determining means 30 for determining the distance to the object to be ranged based on the output of the position detecting means; Lens position setting means 35-44, 46-48 for setting the photographic lens 45
and ripple detection means 9, 14, 1 for detecting whether ripples are included in the light from the object to be measured.
9, 25, non-detection identification means 26 for identifying a state in which the reflected light of the light beam from the object to be measured is not detected by the position detection means, and a non-detection identification means 26 for identifying a state in which a ripple is detected by the ripple detection means and the non-detection detection means 26; an autofocus camera characterized by comprising a correction signal generating means 27 for generating a correction signal for setting the photographing lens at a specific finite distance position when a non-detection state is detected by the means.
This is a new creation. Therefore, in the present invention, when a subject that is bathed in light from an AC light source, for example a fluorescent lamp, is to be measured, the light from the AC light source has a frequency twice as high as the power supply frequency. Since frequency ripples are included, the light reflected from the subject receiving light from such a light source also contains the same ripples. Even if the distance detection result is not detected, if a ripple component from the illumination light source is detected in the reflected light from the object to be measured, the distance detection result will not be judged as ``infinity'', but will be determined as ``specific distance''. This paper proposes a new autofocus camera that makes judgments as being within a finite distance range. The autofocus camera according to the present invention is equipped with a ripple detection circuit that detects whether ripples are included in the ambient light and detects ripples from the object to be measured in order to output the determination results of such a distance measuring device. A distance signal correction circuit that corrects the final judgment result to a ``specific finite distance'' when the distance judgment result based on the reflected light with respect to the light beam is ``infinite distance'' and the ripple detection circuit detects a ripple. It is characterized by providing.

Effects of the Invention Therefore, according to the autofocus camera of the present invention, even if the object to be measured has a low reflectance and is determined to be "infinity" even though it is located at a relatively close distance indoors, etc. If the object is illuminated by an AC light source, it is determined that the object to be measured is within a "specific finite distance" area, and the distance of the photographic lens is adjusted according to the result of this determination. Become. Here, ripples are often detected when the object to be measured is, for example, indoors, and it is considered that the object is not very far away. Therefore, for an object to be measured in such a location, it is better to focus on a ``specific finite distance'', such as the constant focus, than to adjust the focus to ``infinity''. This will increase the probability of getting a suitable photo.

Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings.

Embodiment FIG. 2 is a circuit diagram of a distance measuring device used in an autofocus camera as an embodiment of the present invention.
Light emitting diode 1 and photodiodes 5 to 8 correspond to the circuit shown in FIG. 1, respectively.
When the transistor 59 is turned on at a timing described later, the light-emitting diode 1 discharges the charge of the capacitor 60 that has been charged in advance through the light-emitting diode 1, and emits a single pulse of light. This pulsed light is condensed into a narrow beam by a projection lens and projected toward a distance measuring object, and the reflected light is received by photodiodes 5 to 8. The photodiode 9 is a photoelectric element that receives light from an object to be measured for ripple detection means introduced by the present invention. The amplifier circuits 10 to 14 are as shown in FIG. 3, a specific example of which will be described later, and detect relatively fast-changing AC components contained in the light incident on each photodiode. Convert to voltage signal and output. These amplifier circuits constitute a photoelectric conversion circuit together with a photodiode in the input section. Voltage comparison circuits 15 to 19 each compare the constant voltage level from the reference voltage source 20 with the output level of the amplification circuit, and output a "high" signal when the output level of the amplification circuit is higher. Memory circuit 21
~25 is as shown in FIG. 5 as an example of its configuration.
AND gate 94 and R-S flip-flop 95
are connected in series, and when the voltage levels of the two input terminals become "high" at the same time, each of them memorizes the "high" state and outputs it. Here, the memory circuits 21 to 24 store the output of the previous stage circuit for the reflected light of the light beam from the subject, that is, distance measurement information, and the memory circuit 25 stores the output when ripples are detected from the subject light as described later. , memorize the "high" state.

Next, NOR gate 26, AND gate 27, OR
The circuit consisting of the gates 28 and 29 constitutes a distance signal correction circuit, and the memory circuits 21 to 24 all output "low" (in this state, the measured distance value is "infinite").
), and at the same time, when the memory circuit 25 outputs "high" indicating the presence of ripples,
A signal corresponding to a specific distance range other than the "infinite distance" range, that is, a signal as if the outputs of the memory circuits 23 and 24 were "high" is output to the decoder 30.

The decoder 30 converts the distance signals applied to the input terminals 31 to 34 into signals suitable for the focus adjustment mechanism of the photographing lens 45.
A "high" signal is output from any one of the terminals .about.42. The signal relationship between the input and output of this decoder 30 is shown in FIG.

In FIG. 6, for example, input terminals 31, 32,
The signal states of 33 and 34 are respectively 0, 1, 1,
If it is 0, the output terminal 38 will be "high". In addition, all input terminals 31, 32, 33, and 34 are 0.
(“low”), the output terminal 42 becomes “high”.
This latter state corresponds to the "infinity" region. After the distance information is collected in the memory circuit groups 21 to 25, the photographing lens 45 is retracted by an appropriate driving means, for example, from the closest position to a position in the "infinity" region, and is linked to this operation. The brush 44 is sequentially slid over the contact piece output terminals 35 to 42 and the common terminal 43. When the brush 44 is located on the contact piece output terminal that outputs "high", the transistor 46 becomes non-conductive, the excitation of the electromagnet 47 is cut off, and the locking lever 48 is operated to close the photographing lens 4.
Lock the retraction operation in step 5. In this way, the photographing lens 45 is locked at a position according to the detected distance information and the focus is automatically adjusted.

Next, the input terminals 21a to 2 of the memory circuits 21 to 25
The circuit section that generates the pulse applied to 5a will be explained.

The switch 51 is closed in conjunction with the push of the shutter button SB, and the one shot 52 outputs a "low" voltage for a certain period of time after the switch 51 is closed. The time width of this output is the commercial power frequency
Ripple frequency of illumination light source corresponding to 50Hz 100Hz
The time is set to be longer than one period (1/100 second) of . The circuit shown as block 53 is a valley point detection circuit that detects the point in time when a voltage corresponding to the valley of the ripple is output when a ripple component is output from the amplifier circuit 14. Outputs a “high” pulse. In addition, the amplifier circuit 14
If the output does not include a ripple component, the valley point detection circuit 53 continuously outputs a "high" voltage. For example, as shown in FIG. 4, this valley point detection circuit 53 includes an operational amplifier 87, a constant current source 88 connected to the + side input terminal of the operational amplifier, and a transistor 89.
A capacitor 9 connected in parallel with the transistor
0, resistor 9 connected to the base of transistor 89
1. In FIG. 4, when a positive voltage that does not fluctuate over time is applied to the negative input terminal 92a, the operational amplifier 87
The voltage of the + side input terminal 92b is transferred to the − side input terminal 92a.
The conduction state of transistor 89 is controlled to maintain the voltage equal to the voltage of . In this case, if the circuit constants are appropriately determined, a voltage that can be used as a "high" logic signal is output from the output terminal 93. On the other hand, when a voltage containing ripple is applied to the input terminal 92a, due to the presence of the capacitor 90, the voltage at the input terminal 92b cannot fully follow the voltage fluctuation at the input terminal 92a, and changes as shown in FIG. The output terminal 93 of the operational amplifier 87 switches to low when the voltage across the terminals of the capacitor 90 is higher than the ripple voltage in the ripple valley region, and to high when it is low, and outputs the valley as the output of the valley point detection circuit 53. “High” for each point area
It will output a voltage of .

Now, returning to FIG. 2, the AND gate 54 is
Since a "high" signal is applied from the one shot 52 to the input terminal 54b after a certain time delay from the closing of the switch 51, it responds to the "high" signal applied from the input terminal 54c to the input terminal 54c after the delay of seconds. and outputs a “high” signal. When the flip-flop 55 is in the reset state,
When a "high" voltage is output from the AND gate 54, a "high" voltage is output in response. One shot 56 outputs a "high" voltage for a fixed period of time (for example, 0.5 milliseconds) in response to the reversal of the output of flip-flop 55 from "low" to "high". The "high" voltage from this one shot 56 becomes a storage command signal for the storage circuits 21 to 24, and further becomes a light emission command signal for causing the light emitting diode 1 to emit light.

On the other hand, a "high" voltage is applied to the input terminal 25a of the memory circuit 25 while the one shot 52 outputs a "low" voltage in response to the closing of the switch 51, and during this period, a "high" voltage is applied from the voltage comparison circuit 19. When a "high" voltage is output, the memory circuit 25 stores that a ripple has been detected and outputs a "high" voltage.

Next, the photoelectric conversion circuits forming the amplifier circuits 10 to 14 shown in FIG. 3 will be explained.

In FIG. 3, a circuit consisting of a constant current source 62 and transistors 63, 64, and 65 constitutes a constant voltage circuit for applying a constant voltage to the cathode of a photodiode 61 connected to the base of a transistor 64. The collector of the transistor 66 is connected to a photodiode 61 as a load and a constant current source 72, and further connected to the base of a transistor 69. The transistor 69 has its collector connected to a transistor 67 as a load, and its emitter connected to a constant current source 70, one end of a capacitor 71, and the base of a transistor 66. The transistor 69 functions as an amplification stage that amplifies the relatively high frequency alternating current component of the photocurrent outputted by the photodiode 61, and this function is performed by the transistor 66, which constitutes a negative feedback path to the base of the transistor 69, and the constant current source 70,
This depends on the high-frequency cutoff characteristics of the circuit provided by the capacitor 71. When the photodiode 61 receives light with a constant brightness that does not change over time, and outputs a constant photocurrent corresponding to the light. This photocurrent is combined with the constant current of the constant current source 72, and a part of it becomes the base current of the transistor 69, but most of it becomes the collector current of the transistor 66. In this case, the base current of the transistor 69 is equal to the constant current value of the constant current source 70 times 1/h _FE . However, h _FE is the DC current amplification factor of the transistor 69. Further, the base potential of the transistor 69 is equal to the sum of the base-emitter voltages of the transistors 66 and 69, and remains constant as long as the output current of the photodiode 61 is constant.
Here, suppose that pulsed light is incident on the photodiode 61 in addition to light of constant brightness, and the photocurrent generated by the photodiode 61 in response to this pulsed light temporarily increases. In this case, the transistor 66 is , whose base is biased at a constant level by the capacitor 71 acting as an AC bypass, and even if the photocurrent increases, only the current before the increase is accepted as collector current, so the collector potential of the transistor 66 increases,
The increased photocurrent now flows into the base of transistor 69. Transistor 69 amplifies this increased photocurrent flowing into its base,
Output as collector current. transistor 69
Normally, a constant current from the constant current source 70 is passed through the collector of the transistor 69, so when the photocurrent increases, the collector current of the transistor 69 increases in addition to the above constant current value. . The above is an explanation for the increase in photocurrent, but when the photocurrent decreases, the collector current of transistor 69 decreases by a similar operation. Note that the constant current source 72 is provided here for the purpose of maintaining the circuit including the transistors 66 and 69 in a normal operating state even when no light is incident on the photodiode 61. In this way, the circuit described above amplifies the variation in the photocurrent output from the photodiode 61 and outputs it as the collector current of the transistor 69. The following concerns the circuitry that converts this current signal into a voltage signal.

Transistors 67, 68, and 73 constitute a current mirror, and the collector current of transistor 73 is similar to the collector current of transistor 69. A series circuit of three diode-connected transistors 74, 75, and 76 and a transistor 77 are connected to the collector of the transistor 73, which acts as a load. The voltage appearing at the connection point 78 between these loads and the collector of the transistor 73 is applied to the inverting input terminal 82a of the operational amplifier 82, and is sent out via the terminal 86 as a converted output. Constant current source 79, two diode-connected transistors 80, 81
constitutes a constant voltage source for applying a constant voltage level to the non-inverting input terminal of the operational amplifier 82. The circuit consisting of transistors 83, 84, 77 and capacitor 85 functions as a negative feedback circuit having high-frequency cutoff characteristics to the inverting input terminal of operational amplifier 82. When the transistor 73 outputs a collector current that does not vary with time, its collector potential is changed to the non-inverting input terminal 82b of the operational amplifier 82 by the action of the operational amplifier 82 and the negative feedback circuit connected to this output. maintained at the level of The potential of this terminal 82b is equal to the sum of the base-emitter voltages of the two diode-connected transistors 80 and 81. If the collector current of the transistor 73 is constant, two such base-emitter voltages are applied to a series circuit of three diode-connected transistors 74, 75, and 76. Assume that the collector current of the transistor 73 in steady state is equal to a constant current generated by, for example, a constant current source 79, and
Assuming that the characteristics of transistors 4, 75, 76 and 80, 81 are equal to each other, the current flowing through the series circuit of the three transistors will be several hundredths or less of the collector current of transistor 73 in steady state. Become. This consists of three transistors 74, 75, 7
Transistors 80, 8 on each base-emitter of 6
This is due to the fact that a voltage corresponding to two-thirds of each base-emitter voltage of 1 is applied.

Now, to explain the case where the collector current of the transistor 73 suddenly increases in a pulsed manner,
Transistor 77 has its base biased at a constant voltage by the action of bypass capacitor 85, and, like transistor 66, exhibits a large resistance to an increase in the collector current of transistor 73. Therefore, the increased amount of current flows into the series circuit of transistors 74, 75, and 76, resulting in an increase in voltage proportional to the logarithm of the increased current between the terminals of the series circuit. appear. Conversely, when the collector current of transistor 73 suddenly decreases from its steady value, the resistance between the collector and emitter of transistor 77 apparently decreases, and the voltage level at connection point 78 decreases. As described above, from the output terminal 86,
If the incident light to the photodiode 61 does not change over time, a constant voltage (2V _BE ) is output regardless of its brightness, but if the incident light increases or decreases, the voltage increases or decreases accordingly. A signal is output as a photoelectric conversion output for the pulsed light incident on the photodiode 61.

Next, the overall operation of the circuit shown in FIG. 2 will be explained.

In FIG. 2, it is assumed that the circuit is supplied with power in advance from a power supply (not shown). When the shutter button SB is pressed to take a photograph, the switch 49 is closed and the electromagnet 47 is energized in the first step. At this time, a "high" voltage pulse is generated from the one shot 50 for a certain period of time, the flip-flop 55 and the flip-flops included in the memory circuits 21-25 are reset, and all outputs become "low". In the second step of pressing the shutter button, the switch 51 is closed and a "low" voltage is output from the one shot 52 for a certain period of time. During this time, the memory circuit 25
If it outputs a "high" voltage, this will be memorized. Here, as explained in the circuit of FIG. 3, when light including ripples is incident on the photodiode 9, the amplifier circuit 14 uses a constant voltage (2V _BE ) as a reference according to the ripples. Outputs voltage that fluctuates upward and downward. Therefore, the reference voltage source 20
The output voltage, that is, the determination level of the voltage comparison circuits 15 to 19, is set to a value higher than the above-mentioned constant voltage (2V _BE ) by a constant voltage (for example, 50 mV). In this way, if the peak of the ripple voltage output by the amplifier circuit 14 exceeds the above determination level,
Comparison circuit 19 outputs a "high" voltage. Since the time width of the "low" voltage output by the one shot 52 is set to be longer than the ripple period, the memory circuit 25 is always set when the comparator circuit 19 outputs a "high" voltage at each ripple peak. “High”
It will output a voltage of . When the switch 51 is closed and the one shot 52 outputs a "low" voltage and starts outputting a "high" voltage again,
Both input terminals 54a and 54b of the AND gate 54 are supplied with a "high" voltage. Therefore, if the light from the object to be measured contains ripples that can be detected, the AND gate 54 inputs the input terminal 54.
After the “high” voltage is applied to a and 54b, when the valley point detection circuit 53 actually detects the valley point region of the ripple and outputs the “high” voltage, the “high” voltage is detected. Output voltage. Flip-flop 55 is set in response to a ``high'' voltage from AND gate 54, and its output inverts from ``low'' to ``high'', and in response to this inversion of the output, one shot 56 becomes ``high''. Outputs a single pulse of voltage. This pulse turns on the transistor 59, excites the light emitting diode 1, and emits a light beam. Further, since the pulse of the one shot 56 is used as a storage command to the storage circuits 21 to 24, the distance measurement information is stored in synchronization with the projection of the light beam. In other words, when the shutter button is pressed and the switch 51 is closed,
First, the presence or absence of a ripple is detected while the one shot 52 is outputting a "low" level voltage, and then, if a ripple is present, a light beam is projected at the trough region of the ripple, and the light beam is Distance information is stored in storage circuits 21-24. Therefore, even if ripple components are output from the amplifier circuits 10 to 13 and their peaks are detected and a "high" voltage is output from the amplification circuits 15 to 18 for each ripple peak, this output is output from the memory circuit. The ripple component will not be mixed up with the light reflected by the light beam from the object to be measured. Thus, when the output voltage of the photoelectric conversion circuit corresponding to the reflected light from the object to be measured of the light beam emitted in the valley region of the ripple exceeds the discrimination level determined by the constant voltage source 20, the output of the voltage comparison circuit is It is stored in the memory circuit as information.

Here, if a "high" voltage is output from any one of the memory outputs of the memory circuits 21 to 24,
The output of NOR gate 26 is “low”, AND gate 27
Since the output of is also "low", no correction is applied to the ranging information. Conversely, when a ripple is detected and the outputs of the memory circuits 21 to 24 are all "low", the outputs of the NOR gate 26 and AND gate 27 are "high", and the outputs of the OR gates 28,
29 outputs a "high" voltage, and correction is added to the "infinite" distance measurement information. Thereafter, after the single pulse from the one shot 56 disappears, a focus adjustment operation of the lens 45 is started by a release means (not shown), and then exposure control is performed.

In the embodiment circuit diagram of FIG. 2, dedicated photoelectric conversion circuits 9 and 14 are used to detect ripples.
However, instead of this, the output of any one of the other four photoelectric conversion circuits for detecting distance information may be used.

As detailed above, according to the autofocus camera according to the present invention, even though it is located at a relatively close distance such as indoors, the reflected light beam is reflected due to the low reflectance. Among objects to be measured whose light cannot be detected and are determined to be "infinitely far away," especially those illuminated by an AC light source, If ripples included in the light of This increases the probability of obtaining an in-focus photograph of an object whose distance cannot be measured, further increasing the effectiveness of using this type of camera.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the principle configuration of a known distance measuring device, and FIG. 2 is a circuit diagram showing an embodiment of the present invention.
3 is a circuit diagram showing a specific example of the photoelectric conversion circuit in FIG. 2, FIG. 4 is a circuit diagram showing a specific example of the valley point detection circuit in FIG. FIG. 6 is a circuit diagram showing a specific example of the memory circuit. FIG. 6 is a diagram showing the relationship between the input and output of the decoder in FIG. 2, and FIG. 7 is a diagram showing the operating state of the circuit in FIG. 4. 1...Light emitting diode, 5-8...Photodiode, 10-14...Amplification circuit, 15-19...
Voltage comparison circuit, 21-24... Memory circuit, 30...
... Decoder, 45 ... Lens, 51 ... Switch, 53 ... Valley point detection circuit.

Claims (1)

[Scope of Claims] 1. A light beam projection means having a light projection lens and projecting a light beam toward the object to be measured through the light projection lens; a position detecting means arranged at a position where the light beam is reflected from the object to be measured, and a distance determining means for determining the distance to the object to be measured based on the output of the position detecting means. means, lens position setting means for setting the photographing lens at a position based on the output of the distance determining means, ripple detection means for detecting whether or not the light from the object to be measured contains ripples; a non-detection identification means for identifying a state in which the reflected light of the light beam from the object to be measured is not detected by the position detection means; 1. An autofocus camera comprising: a correction signal generating means for generating a correction signal for setting a photographing lens at a specific finite distance position when an autofocus camera is detected.