JPH0198914A - Range finding device for camera - Google Patents

Abstract

PURPOSE:To obtain a sensor which is free from the influence of variation of reflected light, etc., with the distance of a subject by varying the reference voltage of a comparator which detects a photoelectric output according to a level difference when it is considered that there is a high-low level difference among photoelectric outputs from photodetectors arrayed in the direction of base line length. CONSTITUTION:The respective photocurrent signals from the photodetecting elements S1-S6 arrayed in the direction of the base line length are converted into voltage signals by respective initial-stage operational amplifiers. Those contain even photoelectric signals of DC components due to external light such as the sunshine, but only high-frequency components are inputted to following-stage operational amplifiers because of capacitors for cutting low-frequency components being connected. Here, the photoelectric outputs amplified there by a constant rate are supplied to comparators 17a-17f. Those comparators 17a-17f are applied with reference voltages Vr1-Vr6 corresponding to the level difference obtained by a voltage divider 18 and consequently the comparator 17a securely detects even the photoelectric output of the element S1 applied with feeble reflected light while the amplification factor of the operational amplifier is held constant.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an active type distance measuring device used in a camera.

[Conventional technology]

Active type distance measuring devices, which are often used in recent compact cameras, project a light beam for distance measurement toward the subject, and a light receiving sensor receives the reflected light from the subject. There is. The light-receiving sensor has multiple tiny light-receiving elements arranged in the baseline length direction, and it electrically identifies which of the light-receiving elements the reflected light from the subject is incident on, and measures the distance corresponding to the subject distance. I'm trying to get a signal.

In the distance measuring device described in Japanese Patent Publication No. 55-33005, a plurality of light receiving elements are arranged in the baseline length direction, a constant reference potential is applied to each light receiving element, and the photoelectric output obtained from the light receiving element is referenced. The potential is compared to detect which light receiving element the reflected light is incident on.

Furthermore, in the distance measuring device described in JP-A-54-119267, it is possible to not only identify which of the light-receiving elements arrayed as described above has received the reflected light from the subject, but also identify the two adjacent light-receiving elements. When reflected light is incident across one or three light receiving elements, it is devised so that a distance measurement signal corresponding to an intermediate subject distance when it is incident on each light receiving element can be detected.

Furthermore, in the distance measuring device described in Japanese Patent Application Laid-Open No. 56-29112, when photoelectric outputs appear from a plurality of light receiving elements,
By changing the reference voltage of the comparator connected to each of the light-receiving elements based on the maximum level of photoelectric output, generation of false signals due to crosstalk and the like is avoided.

[Problem that the invention seeks to solve]

However, in the distance measuring device disclosed in Japanese Patent Publication No. 55-33005, if the reference potential is determined according to the light receiving element on the far side that receives weak reflected light from a far object, When strong reflected light enters a photodetector, false signals are generated not only from the specific photodetector but also from adjacent photodetectors due to the effects of crosstalk.
The disadvantage is that it is easy to mismeasure the distance.

Furthermore, although the distance measuring device disclosed in JP-A-54-119267 is advantageous in that the distance that can be detected is greater than the number of light-receiving elements, there is a large level difference in the photoelectric output obtained from each light-receiving element. In order to detect weak photoelectric output separately from noise, the reference potential must be set low. As a result, as mentioned above, erroneous distance measurements due to crosstalk are likely to occur.

Furthermore, the distance measuring device disclosed in Japanese Patent Application Laid-Open No. 56-29112 has the drawback that the structure of the signal processing circuit used in connection with the light receiving sensor is complicated, resulting in high cost.

[Purpose of the invention]

The present invention has been made in order to solve the problems of the prior art as described above, and is not affected by changes in reflected light intensity or crosstalk caused by distance from a subject, and is also capable of signal processing. It is an object of the present invention to provide a distance measuring device for a camera without complicating the circuit.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a comparator for each light receiving element arranged along the base line length direction, and these comparators have different voltages depending on the reference voltage supply means. It is designed to provide a reference voltage of a certain level.

[Effect]

According to the above configuration, if the strength of the reflected light from the subject that enters the photodetector or the photoelectric output from the photodetector is partially amplified by the amplifier and then supplied to the comparator, the amplification factor of the amplifier is Even if there is a level difference in the photoelectric output from each light receiving element due to the magnitude of the photoelectric output, it is possible to reliably detect the presence or absence of the photoelectric output.

An embodiment of the present invention will be described below with reference to the drawings.

[Example] Distance measuring optical system using the light receiving sensor of the present invention 5= In FIG. 2 schematically showing the light projecting section 2, the discharge tube 3. A slit plate 4 that shapes the light from the discharge tube 3 into a slit shape. It consists of a light projecting lens 5. Further, the light receiving section 7 includes a light receiving lens 8. It is composed of a light receiving sensor 9. Each optical axis 5a of the light emitting lens 5 and the light receiving lens 8
, 8a are parallel to the optical axis 10a of the photographic lens 10 and separated by the base line length. As will be described in detail later, the light receiving sensor 9 is formed by arranging small horizontally long rectangular light receiving elements 31 to S6 in the longitudinal direction of the base line.

When a slit light is emitted from the light projection unit 2 toward the subject, a part of the light is reflected by the close subject 12.
The reflected light 12a passes through the light receiving lens 8 to the light receiving element S3.
incident on . Further, when a part of the slit light is reflected from the intermediate-distance subject 13 or the long-distance subject 14, the reflected lights 13a and 14a enter the light receiving elements S2 and 31, respectively. Therefore, among the light receiving sensors 9,
The distance to the object can be determined by detecting which light-receiving element the reflected light from the object is incident on. Note that when a slit light is used as the light beam for distance measurement in this way, the light beam for distance measurement will be irradiated even when the main subject is off the center of the shooting screen, so that it will be possible to This eliminates the need for troublesome operations such as aiming operations and reframing after distance measurement, but distance measurement can also be performed by projecting spot light instead of slit light.

Figure 3 shows the distance range from close range to infinity.
This shows the position where the photographing lens 10 can be set, and the photographing lens 10 is 0.855 m.

Ten positions are set with the optimum focusing positions being 0.935m, 1.05m...5.86m. Here, if the diameter of the permissible circle of confusion is set to 0.025 mm, even if the set position of the photographic lens 10 is 0.855 m, the distance range from 0.807 to 0°893 m will be the focusing range. can be considered.

When the set position of the photographic lens 10 is set in this way, the distance measurement areas R1 to R6 shared by the light receiving elements 31 to S6 are
is as shown in the table below.

As is clear from the above table, the ranging areas R1 to R5 partially overlap. Therefore, reflected light from objects located at a distance of, for example, 1.5 m from the overlapping objects enters both of the light receiving elements 32°S3, and the light receiving elements S2. A photoelectric output will be obtained from S3. Note that the light-receiving element S6 is used for short-range warning, and when a photoelectric output appears only in this light-receiving element S6, this is used as a warning signal.

=7- As shown in FIG. 4, the light receiving sensor 9 is used by being connected to a signal processing circuit 15. The signal processing circuit 15 is
For example, the circuit configuration is as shown in FIG. 1, and each photocurrent signal from the light receiving elements S1 to S6 is converted into a voltage signal by an operational amplifier in the first stage. This voltage signal also includes a DC component, that is, a photoelectric signal caused by external light such as sunlight, but since a capacitor for cutting low frequency components is connected to the output terminal of each operational amplifier in the first stage, it is possible to Only the high frequency components of the photoelectric signal are input to the operational amplifier. The photoelectric outputs each amplified at a constant amplification factor by the next-stage operational amplifier are supplied to signal input terminals of comparators 17a to 17f, respectively.

The reference voltage input terminals of the comparators 17a to 17f have reference voltages Vr, to Vr6 obtained by the voltage divider 18.
is applied. These reference voltages Vr, ~vr6 are lower on the light receiving element Sl side that receives reflected light from a distant object, and are lower on the light receiving element S side that receives reflected light from a nearer object.
The 6th side is high, that is, Vr, <Vr2<...<V
r6. As a result, while keeping the amplification factors of the first and second stage operational amplifiers constant,
Light-receiving element S that receives weak reflected light from a distant subject
Even with a photoelectric output of 1, the comparator 17a can reliably detect. Conversely, for the light receiving element S5 that receives strong reflected light from a close object, the comparator 17
Since the reference voltage VrS of e is set high, false detections due to noise and crosstalk are less likely to occur. When reflected light from a subject enters any of the light receiving elements 31 to S6, the corresponding comparators 17a to 1
A signal output "1" appears at the output end of 7f, and a signal output "0" appears when no reflected light is incident.

By the way, as described above, the light receiving elements 31 to S5 each receive reflected light from a subject within the ranging areas R1 to R5 having a certain width, and the comparator 1 responds to this.
It is necessary to obtain a photoelectric output that causes the output terminals of 7a to 17f to output a signal output of "1". Therefore, the widths D1 to D5 of the light receiving elements 31 to S5 in the baseline length direction are determined as shown in FIG. 5. In FIG. 5, the right end of the light receiving element S1 is the farthest position of the ranging area R1.
, 27 meters away from the subject. The detection level of the photoelectric output at this time is set as a level at which the second-stage operational amplifier output of the signal processing circuit 15 is two to three times larger than the noise level.

After determining the right end of the light-receiving element S1 in this way, move the subject to the nearest position of the distance measurement area R1, 2.19 m,
The left end of the light receiving element Sl is determined at a point where a photoelectric output equal to the initial detection level can be obtained, and thereby the width D1
Determine. For example, after determining the right end position of the light receiving element S1 and moving the test subject to a position of 4.27 m, the mask covering the front surface of the light receiving element S1 is opened in the baseline length direction, and the detection level is This corresponds to the amount of movement of the mask when the photoelectric output is obtained. Of course, instead of performing such a simulation, it is also possible to determine the width D1 by computer analysis.

After determining the width D1 of the light receiving element S1 in this manner, the right end of the next light receiving element S2 is brought close to the left end of the light receiving element S1, and the subject is placed at the farthest position of the ranging area R2, that is, at a position of 2.86 m. After measuring the detection level of the photoelectric output at that time, the subject is moved to the nearest position 1. in the distance measurement area R2.
46 m, and determine the closest end of the light receiving element S2 at the point where the photoelectric output at that time matches the measured detection level. As a result, the width D2 of the light receiving element S2 is determined, and the width D3 of each of the light receiving elements S3 to S5 is determined in the same manner.
~ Decide on D5. In addition, it is also possible to provide an appropriate gap at each boundary without bringing the light receiving elements 31 to S5 into close contact with each other.

Binarized signal outputs A1 to A6 appearing at the output terminals of the comparators 17a to 17f are supplied to an AF control circuit 20. FIG. 6 shows an example of the AF control circuit 20. This A Fi# control circuit 20 is activated, for example, by pressing the shutter button halfway. When the power supplies ■ and c are applied, a reset pulse is output from the reset pulse generation circuit 23 after waiting for the stabilization of the power supply VCC, and this resets the RS flip-flop circuit FFO that controls the opening and closing of the AND gate 24. Signal to terminal - "1"
” appears and the AND gate 24 is opened.

The microcomputer 22 in FIG. 4 outputs a clock pulse to the AF control circuit 20 after a delay of 100 m5ec after the shutter button half-press signal is input. This clock pulse is supplied to counter 25 through AND gate 24 .

A decoder 26 is connected to the counter 25.
6 controls the distance measurement sequence in accordance with the clock pulse count value of the counter 25. The decoder 26 includes D flip-flop circuits DFF1 to circuit F for latching signal outputs A1 to A6 from the signal processing circuit 15.
6 (hereinafter simply referred to as DFF 1 to DFF6) and the shift register 28. after that,
AF) outputs the trigger pulse to the strobe control circuit 29.

The strobe control circuit 29 is constructed as shown in FIG. 8, and the discharge tube 3 emits light when the AF trigger pulse is supplied to the terminal T5. After the AF trigger pulse is output, the counter 25 counts the clock pulses for a predetermined period of time until the strobe light from the discharge tube 3 reaches its peak. A read pulse with a time width is output from the decoder 26. This read pulse is input to one of the AND gates G1 to G6 connected to the clock terminals of DFFI to DFF6. therefore,
In this way, while the AND gates G1 to G6 are opened by the read pulse, if there is a signal value "1" among the signal outputs A1 to A6 from the signal processing circuit 15, the corresponding one among DFF1 to DFF6 is detected. will be set.

Among DFF1 to DFF6, a signal "1" appears at the Q terminal of the one set by the signal value "1" among the signal outputs A1 to A6, and this is input to the shift register 28.
It is stored in a predetermined bit location. Therefore, for example, the signal values of the signal output A I -A 6 are ro'', ro'',
rl”, ra”.

rl'' and r□'', the shift register 28 stores the distance measurement data of rololo. After outputting the read pulse, the decoder 26 outputs a shift pulse to the shift register 28.

As a result, the distance measurement data stored in the shift pulse 28 is sequentially transferred to the microcomputer 22.

After outputting a predetermined number of shift pulses to the shift register 28, the decoder 26 outputs a ranging completion signal. This ranging completion signal is supplied to the set terminal of the FFO via the inverter 29, thereby putting the FFO in the set state. As a result, the FFO (terminal output) becomes "0", the AND gate 24 is closed, and the distance measurement sequence is completed.

The microcomputer 22 compares the distance measurement data input from the AF control circuit 20 with the AF element table 0 to determine the set position of the photographic lens 10. AF child table 0
is constructed as shown in FIG. 7, and includes light receiving elements 81 to S6.
In addition to the light reception pattern, that is, the distance measurement data described above, the set position of the photographic lens 10 is determined in consideration of the subject brightness data (EV value) detected by the photometry circuit 31. This is to accommodate the fact that the maximum aperture of the program shutter changes depending on the EV value, and to make maximum use of the depth of field. In addition, the lens set positions represented by Nr, N2,..., N, in the AF child table 0 in Fig. 7 are 0,855m, shown in Fig. 3.
0.935m...

This corresponds to the lens set position where the optimum focusing position is 5.86 m.

When the lens set position is determined in this manner, the microcomputer 22 outputs a number of drive pulses corresponding to the lens set position to the motor drive circuit 32. As a result, the stepping morph 33 rotates by a predetermined amount, and the photographing lens 1
0 is moved to the determined lens set position.

The AF element table 0 also stores control data for a built-in strobe 35 that provides auxiliary illumination to a low-brightness subject, that is, light emission timing data for the built-in strobe 35, as shown enclosed by a broken line. And the lens set position is A
In the case determined by the data surrounded by the broken line in the AF element table 0, when the program shutter reaches the aperture diameter stored in the AF element table 0 due to the operation of the shutter drive circuit 36, the microcomputer 22 performs strobe control. A light emission trigger signal is output to the circuit 37, and the built-in strobe 35 is operated to emit light. Note that FIG. 8 shows an example of the strobe control circuit 29, where terminal T is a charging inhibit signal input terminal, terminal T2 is a charging start signal input terminal, and terminal T3 is an A terminal.
The charging completion signal output terminal of the F discharge tube 3 and the terminal T4 are the light emission trigger signal input terminals of the built-in strobe 35, and are connected to the microcomputer 22, respectively. Further, the terminal T5 is used as an input terminal for the AF trigger pulse output from the AF control circuit 20.

〔Effect of the invention〕

As explained above, according to the distance measuring device of the present invention, when a difference in high and low levels is expected in the photoelectric output output from each of the plurality of light receiving elements arranged in the baseline length direction, The reference voltage of a comparator that detects the presence or absence of photoelectric output is changed in accordance with the level difference.

Therefore, compared to the conventional technology that detects the presence or absence of each photoelectric output from a plurality of light-receiving elements using a comparator to which a constant reference voltage is applied, Furthermore, it is possible to obtain a good ranging function that is not affected by false signals due to crosstalk.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention. FIG. 2 is a schematic diagram of a distance measuring optical system using the present invention. FIG. 3 is an explanatory diagram showing the relationship between the set position of the photographic lens and the distance measurement area. FIG. 4 is a block diagram showing the circuit configuration of the distance measuring device. FIG. 5 is an explanatory diagram showing the outline of the configuration of the light receiving sensor and the correlation between photoelectric outputs. FIG. 6 is a circuit diagram showing an example of an AF control circuit. FIG. 7 is a conceptual diagram of an AF element table that determines the lens set position. FIG. 8 is a circuit diagram showing an example of a strobe control circuit. 2... Light projecting section 7... Light receiving section 9... Light receiving sensors 81 to S6... Light receiving elements R1 to R6... Ranging area 10... Photographing lens 15... Signal processing circuit 20... AP control Circuit 30...AF child table

Claims (2)

[Claims] (1) In a camera distance measuring device that receives light reflected by a subject out of the luminous flux projected from a light projecting means by a plurality of light receiving elements arranged in the baseline length direction, a distance measuring device provided for each of the plurality of light receiving elements. The device is equipped with a comparator into which each photoelectric output is input, and a reference voltage supply means for supplying reference voltages of different levels to these comparators, and detects the presence or absence of photoelectric output at different comparison levels for each light receiving element. A distance measuring device for a camera, characterized in that: (2) The reference voltage is set to be lower as it is supplied to a comparator provided corresponding to a light receiving element located at a farther distance. range device.