JPH058575Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a distance measuring device for an autofocus camera.

[Prior Art] Conventionally, as this type of distance measuring device, a triangular distance measuring device is used, in which light emitted from a light emitting element is projected toward a distance measurement target, and the reflected light is received by two adjacently arranged light receiving elements. A distance measuring device based on this method is known.

FIG. 3 shows a light receiving circuit portion of a distance measuring device used in a conventional autofocus camera. The circuit in the figure includes light receiving elements S1, S2 such as photodiodes,
Optical signal detection resistors R1 and R2 connected in series to the light receiving elements S1 and S2, respectively, and the light receiving elements S1 and S2.
DC voltage is applied to each series circuit of 2 and resistors R1 and R2.
A battery (not shown) that supplies Vcc, capacitors C1 and C2 whose one ends are connected to the connection points between light receiving elements S1 and S2 and resistors R1 and R2, and input terminals connected to the other ends of these capacitors C1 and C2. The circuit includes amplifiers A1 and A2, logarithmic compression diodes D1 and D2 connected in the forward direction between the output terminals of the amplifiers A1 and A2 and the negative terminal of the battery, a differential amplifier A3, and comparators CP1 to CP4. .

Next, the operation of the circuit shown in FIG. 3 will be explained. During distance measurement, a light emitting element (not shown) is driven in a pulsed manner.
Emit single or multiple pulsed light. This light is irradiated onto an object (not shown) and reflected by the object. The reflected light from the object enters the light receiving elements S1 and S2 through a lens (not shown), and the resistance value of each light receiving element S1 and S2 changes, and a pulse signal corresponding to the distance of the object is generated between the terminals of the resistors R1 and R2. V _P1 ,
V _P2 occurs. These pulse signals V _P1 and V _P2 are separated from the DC voltage components V _D1 and V _D2 caused by external light from the subject etc. by capacitors C1 and C2.
After being amplified by amplifiers A1 and A2 and logarithmically compressed by diodes D1 and D2, it is input to differential amplifier A3. As a result, the differential amplifier A
3 is the ratio of the above two pulse signal voltages V _P2 /V _P1 ,
That is, it outputs a voltage V _A according to the distance to the subject. Comparators CP1 to CP4 compare this output voltage V _A with different reference voltages V _S1 to V _S4 , respectively. The outputs of the comparators CP1 to CP4 are supplied to a lens drive circuit (not shown). In the lens drive circuit, these comparators CP1~
It performs logical calculations on the output of the CP4, drives the photographing lens according to the results of the calculations, and executes automatic focusing (AF).

[Problems to be solved by the invention] By the way, in the above configuration, in order to improve the accuracy of AF, increase the light emitting power and increase the distance signal light from the subject.Increase the photoelectric conversion efficiency of the light receiving elements S1 and S2. Countermeasures can be taken to reduce the overall noise component, especially on the input side. However, there are theoretical limits to , and there are physical limits to .

As an alternative to the above, the resistance values of R1 and R2 are often increased to make the distance signal light appear larger. However, this method also has its limitations. In other words, the two light-receiving elements S1 and S2 that perform triangulation generate a current _ID due to external light and _IP1 and _IP2 due to the subject distance signal light, and voltages V1 = ( _ID + _IP1 ) and V2 = ( _ID + _IP2 ) are generated between the terminals of the signal detection resistors R1 and R2, respectively.

However, since the maximum current flowing through this resistor R1 is Vcc/R1, the amount of external light is I _D1 = R1
If it becomes more than that, the voltage between the terminals of resistor R1 is V1=
It is saturated at Vcc, and even if the signal light I _P1 tries to flow, the voltage V1 does not change, and the signal light I _P1 is no longer detected. This also applies to the other light receiving element S2 and resistor R2. In other words, in such a distance measuring device, the resistance R1 is
There are conflicting conditions: it is better to be small in order to increase external light resistance (dynamic range), and it is better to be large in order to increase signal light detection ability (S/N ratio). For this reason, in conventional distance measuring devices, when trying to improve the signal light detection ability, the tolerance to external light decreases, and when the brightness of external light is high, distance measurement becomes impossible and the autofocus function does not function, making it difficult to take pictures. There was an inconvenience that the photos were sometimes out of focus.

SUMMARY OF THE INVENTION In view of the above-mentioned problems with the conventional type, an object of the present invention is to improve the signal light detection ability of a distance measuring device for an autofocus camera without impairing external light resistance.

[Means for Solving the Problems] In order to achieve the above object, the present invention projects light emitted from a light emitting element toward a distance measurement target, receives the reflected light by a light receiving element, and the light receiving element In an autofocus camera distance measuring device that converts the current of It is characterized by switching values.

[Operations and effects of the invention] According to the above configuration, the resistance value is increased in normal times to improve the signal light detection ability (distance measurement sensitivity), and the resistance value is increased when the aperture is small (small aperture diameter, large aperture value). By lowering the value, resistance to external light is ensured. Note that when using a small aperture, the distance measurement accuracy decreases by lowering the distance measurement sensitivity, but since the depth of focus of the camera lens is deep, some distance measurement errors are not a problem. Also. Since it is common to use a small aperture when the brightness of outside light is high, there is no problem with the resistance to outside light when the brightness of outside light is high.

[Example] Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the circuit configuration of an autofocus (AF)/autoexposure (AE) camera according to an embodiment of the present invention. Note that parts in FIG. 1 that are common or corresponding to those in FIG. 3 are denoted by the same reference numerals.

The distance measuring circuit AF in Figure 1 is different from the one in Figure 3.
Divide the resistor R1 of the light receiving part 1 into resistors R _1A and R _1B ,
A transistor is connected to both terminals of one resistor R _1B.
Connect the collector and emitter of TR1, and connect the automatic exposure circuit AE to the base of this transistor TR1.
The aperture value signal Vf generated by the aperture value signal Vf is applied. Furthermore, a series circuit of resistor Rg2 and the collector-emitter of transistor TR2 is connected in parallel with feedback resistor Rg1 that determines the amplification factor of amplifier A1, and the aperture value signal Vf is applied to the base of transistor TR2 in the same way as transistor TR1. I try to do that. The light receiving section 2 is similarly configured.

The automatic exposure circuit AE includes a light receiving element S3 and an amplifier A.
4. A logarithmic compression diode D3 for making the amplifier A4 a logarithmic compression type amplifier, a voltage source V _ISO that generates a reference voltage as film sensitivity information, a transistor TR3, a second release switch SW, a time capacitor Ct, a comparator CP5, It includes a CP6, a solenoid L, a reference voltage source V _AF for high brightness discrimination, a reference voltage source V _AE for low brightness discrimination, a reference voltage switching switch RY, a controller CNT, and the like.

Next, the operation of the circuit shown in FIG. 1 will be explained.

First, the operation of the automatic exposure circuit AE will be explained. Note that this circuit AE starts opening at a predetermined speed when the second release switch SW is pressed (second release) and starts closing when a time corresponding to the external light brightness has elapsed, so the opening time and opening degree (aperture diameter ) is used to control a so-called program shutter in which both change.

When external light is incident, the light receiving element S3 generates a signal corresponding to the brightness of the external light. A logarithmic compression amplifier consisting of amplifier A4 and diode D3 amplifies this signal. The voltage source V _ISO controls the compression rate in the logarithmic compression amplifier by biasing the external light brightness signal output from the light receiving element S3 according to the film sensitivity information. The output of amplifier A4 is fed to the base of transistor TR3, which is set to operate in the active region. As a result, a current obtained by logarithmically expanding the base voltage, that is, a current proportional to the external light brightness detected by the light receiving element S3 flows through the collector of the transistor TR3.

When the first release switch (not shown) of this camera is pressed, a power supply voltage is applied to the capacitor Ct, and when the second release switch SW is subsequently pressed and turned off (opened), this transistor is turned off.
The collector current of TR3 flows and is charged. Further, by pressing the second release switch, an aperture blade drive mechanism (not shown) operates, and the shutter (aperture blade) begins to open. On the other hand, with the above charging, the voltage between the terminals of the capacitor Ct increases, and the input voltage to the comparator CP5 decreases. and,
When this input voltage becomes lower than a predetermined reference voltage V _R , the solenoid L is driven by the comparator CP5 to operate an aperture blade release mechanism (not shown), and the aperture blades are returned to the shutter closed position by a return spring (not shown). . As described above, the shutter is driven open for a period of time corresponding to the brightness of outside light.
Since this change in opening driving speed is constant regardless of the shutter opening time, the shutter opens to an opening degree (aperture diameter) corresponding to the brightness of external light.

Controller CNT is CPU (Central Processing Unit)
etc., and controls the overall operation of this camera. In other words, when the first release switch is pressed, the reference voltage switching switch is first pressed.
RY is switched to the high brightness discrimination side V _AF and the output of the comparator CP6 is inspected to determine whether the controlled aperture value (output voltage of amplifier A3) is larger or smaller than the first set value V _AF . Next, switch RY is switched to the low brightness discrimination side V _AE , the output of comparator CP6 is checked, and the above-mentioned controlled aperture value is the second set value.
Determine whether it is greater or less than V _AE . continue,
As a result of the above-mentioned high brightness discrimination, the controlled aperture value is the above-mentioned first
If the aperture value is larger than the set aperture value V _AF , an H level small aperture detection signal Vf is output. Furthermore, as a result of the above brightness determination, if the controlled aperture value is smaller than the second set aperture value V _AE , the shutter open time will be longer and there is a risk of camera shake, so a low brightness warning signal will be output to prevent camera shake. do. And distance measuring circuit AF
A distance measurement start command signal is sent to prepare for the second release. Note that the operations after the second release are the same as those of the conventional one.

Next, the action of the distance measuring circuit AF is shown in Fig. 2, which shows the voltage V between the terminals of the optical signal detection resistor R1 with respect to the brightness of external light.
This will be explained with reference to the input/output characteristic diagram shown in 1. In this distance measuring circuit, the transistor TR1 is turned off while the brightness of external light incident on the light receiving element S1 is low and the aperture value is small. Therefore, the light receiving element S1
Resistance value R1 (=R _1A +
R _1C ) increases, and the input/output characteristics switch to the side with higher signal light detection ability (solid line in FIG. 2). On the other hand, when the brightness of external light incident on the light receiving element S1 is high and the aperture value is larger than the first set value, the transistor TR1 is turned on by the aperture value detection signal Vf=“H” from the controller CNT, and the resistor _R1C is turned on. short circuit. Therefore, the resistance value R1 (=R _1A ) for detecting the current of the light-receiving element S1 becomes low, and the input/output characteristics are switched to the side with higher resistance to external light (the broken line in FIG. 2). In other words, it is possible to set the signal light detection ability at a normal (large aperture) high, and to ensure external light resistance when a small aperture is used, that is, high brightness.

In addition, in this distance measuring circuit, transistor TR2
The amplification factor of the amplifier A1 is switched by. In other words, the transistor TR2 is turned on by the aperture value detection signal Vf=“H” at the time of the small aperture, the resistor Rg2 is connected in parallel to the feedback resistor Rg1 of the amplifier A1, and the photodetection resistor R1 is made small, so that light is detected. The gain of the amplifier A1 is increased by an amount corresponding to the decrease in capability (gain) to compensate for the decrease in ranging sensitivity.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of the main parts of an autofocus camera according to an embodiment of the present invention, and Fig. 2 shows the input/output characteristics of the distance measuring circuit in Fig. ₁ . FIG. 3, which is a diagram expressed in terms of the terminal voltage V1, is a circuit diagram of a conventional distance measuring circuit. S1, S2, S3... Light receiving element, R1, R2,
R _1A , R _1B ...Resistance for optical signal detection, TR1, TR2
...Transistor, A1, A2, A3...Amplifier, Rg1, Rg2...Feedback resistor, D1, D2, D
3... Logarithmic compression diode, A3... Differential amplifier, CP1 to CP6... Comparator, CNT...
Controller, Vf...Aperture value detection signal.

Claims (1)

[Claims for Utility Model Registration] 1. A light-emitting element that projects pulsed light toward a distance measurement object, a light-receiving element that receives reflected light from the distance-measuring object, and a first light-emitting element connected in series to the light-receiving element. a DC power supply that applies a voltage to the series circuit of the light receiving element and the resistor, an amplifier that amplifies the pulse voltage generated in the first resistor by the reflected light, and a distance to the subject based on the output of the amplifier. an aperture value detection circuit for detecting a set aperture value of a camera lens; and means for switching the resistance value of the first resistor in accordance with the aperture value. Focus camera ranging device. 2. The resistance value switching means includes a switching element that is turned on and off based on the output of the aperture value detection circuit, and a switching element that is turned on and off based on the output of the aperture value detection circuit;
Utility model registration claim 1 comprising a resistor and a second resistor connected in series or in parallel.
Distance measuring device described in section. 3. A utility model registration according to claim 2, which is attached to a camera together with an automatic exposure device, and the aperture value detection circuit detects the aperture value based on an aperture control signal generated by the automatic exposure device. distance measuring device. 4. The distance measuring device according to claim 3, wherein the gain of the amplifier is switched in conjunction with switching the resistance value by turning on and off the switching element.