JPH07174963A - Range-finding device for camera - Google Patents

Abstract

PURPOSE:To rapidly perform the operation from starting light projection to the focusing of a photographing lens by deciding the gain of an amplifier circuit by performing preliminary light emission in the case of amplifying an optical signal from a subject, easily obtaining a subject distance from the decided gain, and focusing the photographing lens without starting normal light emission. CONSTITUTION:When a range-finding routine is started, the power sources of all the circuits are turned on, first. Next, a CPU 80 clears the contents of a storage device (RAM) 81 capable of reading/writing, and decides the optimum gains of the amplifier circuits 40 and 50. The gain is decided by the preliminary light emission. In the case of deciding that the subject is at a position within a certain distance while performing operation for deciding the gain, it is judged as being the closest without performing range-finding because a closest flag in the RAM 81 is set. Since values S1 and S2 are decided while performing the operation for deciding the gain, a lens barrel 86 is driven based on the moving amount of the photographing lens stored at the address of a ROM 82 univocally decided from the values.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distance measuring device such as a camera, and more particularly to an active type distance measuring device for a camera.

[0002]

2. Description of the Related Art Conventionally, various active distance measuring devices have been proposed, but when amplifying an optical signal from a subject in these distance measuring devices, first, the light is projected several times to gain the gain of an amplifier circuit. (Hereinafter, this is referred to as preliminary light emission), and thereafter, the light projecting circuit is operated for a predetermined number of times or time (hereinafter, this is referred to as main light emission),
The distance to the subject was calculated from the output result, and the taking lens was focused.

[0003]

However, in the distance measuring device as described above, the optimum gain of the amplifier circuit constituting the light receiving circuit is first determined by the preliminary light emission, and the subject distance is calculated by the main light emission. It takes a very long time from the start of light to the focusing of the taking lens, which in turn causes a missed photo opportunity.

[0004]

In order to solve the above problems, in the distance measuring apparatus for a camera according to the present invention, a light projecting means for irradiating a subject with light, and the light projected from the light projecting means is reflected by the subject. A light receiving means for receiving light and converting it into two currents;
A first current-voltage conversion circuit that converts one output current of the light-receiving means into a voltage; a second current-voltage conversion circuit that converts the other output current of the light-receiving means into a voltage; the first or second Selecting means for selecting the output of the current-voltage conversion circuit, an amplifier circuit for amplifying the output signal selected by the selecting means, and an integrating circuit for integrating the output signal of the amplifier circuit,
Based on a comparison unit that compares the output signal of the integration circuit with a predetermined signal, a gain adjustment selection unit that adjusts the gain of the amplification circuit based on the comparison result of the comparison unit, and an adjustment result of the gain adjustment unit. And a calculation means for obtaining a distance signal to the subject.

[0005]

When the optical signal from the subject is amplified, preliminary light emission is performed to determine the gain of the amplifier circuit, and the subject distance is easily obtained from the gain to focus the photographing lens without entering the main light emission.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of an embodiment of the present invention will be described with reference to FIG. The light projecting circuit 10 is a near infrared light projecting element (hereinafter, IRED).
A driving circuit for driving a transistor 14, a base resistor 12, a collector resistor 13 and an IRED 14. Arithmetic circuit (hereinafter referred to as CPU)
When the light projection signal is output from 80, the IRED 14 emits light. The emitted light passes through the light projecting lens 1, a part thereof is reflected by a subject (not shown), and a part of the reflected light passes through the light receiving lens 2 and is incident on a semiconductor position detecting element (hereinafter referred to as PSD) 3. In the present invention, the IRED 14 is pulse-driven.

Current-voltage conversion circuits 20 (far side) and 30
(Near side) constitutes a light receiving circuit together with PSD3. When an optical signal is incident on the PSD 3, the PSD 3 generates a current according to its intensity and incident position in the current-voltage conversion circuit 20.
And output to 30. The current-voltage conversion circuit 20 has an amplifier 21.
Is a circuit configured to output a voltage proportional to an input current, the current-voltage conversion circuit 30 includes an amplifier 31 and a feedback resistor 32, and has the same configuration as the current-voltage conversion circuit 20. A voltage corresponding to the current is output and guided to the switch 4.

The switch 4 has a role of transmitting the output of one of the current-voltage conversion circuits 20 and 30 to a circuit in the subsequent stage, and its state is controlled by the CPU 80. When the distance measurement on the long distance side is performed, the current-voltage conversion circuit 20 is turned on, and when the distance measurement on the short distance side is performed, the current-voltage conversion circuit 30 side is turned on.

The amplifier circuits 40 and 50 are gain switchable amplifier circuits. Since these circuits have exactly the same configuration, the amplifier circuit 40 will be described as an example. Amplifier circuit 4
A coupling capacitor 5 is connected before 0, and the DC component of the input signal is cut off here. The amplifier circuit 40 is a circuit configured of an amplifier 41 and three feedback resistors, and amplifies an input signal with a certain gain. There are two switches 46 and 47 in the circuit, and these switches can be turned on / off by the CPU 80.
Since the switch 46 turns on / off the feedback resistor 43 and the switch 47 turns on / off the feedback resistor 43 and the feedback resistor 44, respectively, the gain of the amplifier 41 changes stepwise depending on the states of these switches, and the gain depending on the changed gain. It is amplified and output to the amplifier circuit 50. The amplifier circuit 50 also operates in exactly the same manner, and the CPU 80 operates the switches 56 and 57 to set an appropriate gain, and the signal output from the amplifier circuit 40 is amplified accordingly. The output signal of the amplifier circuit 50 is output to the integrating circuit 60 in the subsequent stage via the switch 7.

The integrating circuit 60 includes an amplifier 61 and an input resistor 6
2, integrating capacitor 63, switch 64, voltage follower 6
5 is a circuit configured to integrate the input voltage with time. Prior to the integration operation, the switch 64 is turned on to discharge the electric charge remaining in the integration capacitor 63. When fully discharged, the switch 64 turns off. When the integration operation is started by turning on the switch 7, the time integration value of the input signal is stored in the integration capacitor 63 as electric charge. The value of the voltage between the terminals of the integrating capacitor 63 at this time is output to the comparator 71. When the integration operation is completed, the switch 7 is turned off.

The level determination circuit 70 is a circuit configured by a comparator 71 and a reference power source 72 for determining the level of the input voltage. The comparator 71 compares the value of the input voltage with the voltage V1 of the reference power source 72, and outputs the “H” level to the CPU 80 if the input voltage is higher, and outputs the “L” level to the CPU 80 if the input voltage is lower.

Next, the operation of the circuit according to the embodiment of the present invention will be described. When this distance measuring routine is entered, first, the power supplies of all the circuits in FIG. 1 are turned on. Next, the CPU 80 clears the contents of a readable / writable storage device (hereinafter referred to as RAM) 81 and determines the optimum gains of the amplification circuit 40 and the amplification circuit 50. If it is determined in this gain determination operation that the subject is at a position less than a certain distance, the close-up flag in the RAM 81 is set, and in that case, it is determined that the close-up is performed without performing distance measurement. Among the above gain determination operations,
Since the values S1 and S2 are determined, the lens barrel 86 is driven based on the photographing lens drive amount stored in the address of the ROM 82 that is uniquely determined from these values. Finally, the power of the distance measuring circuit is turned off, and this routine is exited.

Next, the gain determining operation of the amplifier circuit 40 and the amplifier circuit 50 for the current-voltage conversion circuit 20 will be described with reference to FIGS. 2 and 3. First, the CPU 80 turns on the switch 4 to the current-voltage conversion circuit 20 side. Switch 6
4 is turned on to discharge the electric charge accumulated in the integrating capacitor 63 (FIG. 2a). After discharging the electric charge sufficiently, the switch 64 is turned off, and the value N1 of the counter 83 is cleared to 0 by the count reset signal CR (FIG. 2).
b). Then, the CPU 80 operates the light projecting circuit 10 to start light projecting. In order to secure the rise time of each amplifier due to the start of light emission and reduce the influence of power supply fluctuation, after the time T1 after light emission has passed (FIG. 2c), the integrating circuit is operated only for the time T2. After that, projection and integration are stopped (Fig. 2d), and the device waits for the time T3 (Fig. 2d).
e), 1 is added to the counter by the count-up signal CU.

After repeating this operation for a predetermined number of times Ng (for example, 10 times) as shown in FIG.
The voltage between the terminals of the integrating capacitor 63, that is, the integrated voltage Vi
Is compared with the voltage V1 of the reference power source 72 by the comparator 71 and the result is converted into a digital signal and output to the CPU 80. When the output of the comparator 71 is H level (FIG. 2f), the CPU 80 turns on the switch 46. In the same manner, the integration operation and the comparison operation are repeated in the same manner, and the comparator 7
If the output of 1 is H level, switch 56, switch 47,
The switches 57 are turned on in this order. Even if all the switches are turned on, if the output of the comparator 71 is at H level, the near flag is set. As described above, the optimum gains of the amplification circuit 40 and the amplification circuit 50 for the current-voltage conversion circuit 20 are determined.

The above is the operation of the circuit in this embodiment. The above operation is shown in a flow chart in FIGS.
become that way. First, the main routine will be described with reference to FIG. When this distance measuring routine is entered, the CPU 80 turns on the power supply of the entire distance measuring circuit (# 001) and clears the contents of the RAM 81 (# 002). Next, the optimum gain determination operation in the current-voltage conversion circuit 20 is performed to determine the value S1 that is uniquely determined by the gain and save it in the RAM 81 (#
003), and further, the optimum gain determination operation in the current-voltage conversion circuit 30 is performed, and the value S2 uniquely determined by the gain is obtained.
Is stored in the RAM 81 (# 004). Next, the state of the closest flag is confirmed (# 005), and if it is set, the closest distance (for example, 0.
5m) (# 006) and jump to # 008. Here, DV is an area of a fixed length reserved in the RAM 81. If the near flag is not set, RA
R to be referred to from the value S1 and the value S2 in M81
The address of the OM 82 is generated (# 007), the drive amount of the lens barrel 86 stored at that address is read out, and the DV is read.
(# 008), the motor 85 is controlled based on DV to drive the lens barrel 86 to the in-focus position (# 00).
9). Finally, the power supply of the distance measuring circuit is turned off (# 010), and the routine is exited to start the exposure operation.

Next, the operation within each subroutine will be described. First, the subroutine for determining the value S1 will be described with reference to FIG. The value S1 is 1-byte data held at an appropriate address in the RAM 81. When entering the subroutine for determining the gain of the amplifier circuit in the subsequent stage, the CPU 80 turns on the switch 4 to the current-voltage conversion circuit 20 side (# 101),
The value S1 is cleared to 0 (# 102), the switch 64 is turned on to discharge the charge accumulated in the integrating capacitor 63 (# 103), and the value N1 of the counter 83 is cleared to 0 (# 104).

Subsequently, the CPU 80 operates the light projecting circuit 10 (# 105) and waits for the time T1 (# 10).
6), the switch 7 is turned on to perform the integral operation (# 1
07), wait for time T2. During this time, electric charge is stored in the integrating capacitor 63 (# 108). Then, the operation of the light projecting circuit 10 is stopped to end the light projecting operation, and the switch 7
Is turned off to complete the integration operation (# 109), wait for time T3 (# 110), and add 1 to the counter 83 (# 1).
11). If the value N1 of the counter 83 is less than the predetermined number of times Ng, the process jumps to # 105 (# 11
2). If the value N1 is equal to or more than the number of times Ng, the integrated voltage Vi is output to the comparator 71, which compares the voltage with the voltage V1 of the reference power supply 72, and as a result, the voltage Vo.
Is output to the CPU 80 (# 113). The CPU 80 determines the level of the voltage Vo (# 114), and if it is at the H level, returns to the main routine.

When the voltage Vo is at L level, the CPU 8
For 0, add 1 to the value S1 (# 115), check whether the value S1 is equal to 1 (# 116), and if they are equal, turn on the switch 46 to reduce the gain of the amplifier 41 (# 117). ), Jump to # 103. Next, it is confirmed whether or not it is equal to 2 (# 118), and if they are equal, the switch 56 is turned on to further reduce the gain of the amplifier 51 (# 119), and the process jumps to # 103. Next, it is confirmed whether or not it is equal to 3 (# 120), and if they are equal, the switch 47 is turned on to further reduce the gain of the amplifier 41 (# 121), and the process jumps to # 103. Then 4
(# 122), and if they are equal, the switch 57 is turned on to further reduce the gain of the amplifier 51 (# 123), and the process jumps to # 103. Value S
If the value of 1 is neither 0 nor 3, the close flag in the RAM 81 is set (# 124), the process exits this subroutine and returns to the main routine.

Next, FIG. 7 shows a subroutine for determining the value S2. The operation is almost the same as the case of determining the value S1, and C
The PU 80 turns on the switch 4 to the side of the current-voltage conversion circuit 20, and determines an appropriate gain while adding 1 to the value S2 which is 1 byte of data held at an appropriate address in the RAM 81. When exiting this routine, either the value S2 that is uniquely determined by the gain is determined, or the near-field flag in the RAM 81 is set.

In this embodiment, a PSD having two electrodes is used as a light receiving element, but a PSD having an intermediate electrode or the like is used.
It goes without saying that a light receiving element composed of one or more electrodes, especially an element such as a split photodiode (SPD) may be used.

Further, in the present embodiment, the two current-voltage conversion circuits share one amplification circuit by the switch, but each current-voltage conversion circuit is connected with a separate amplification circuit which is equivalent to the circuit. The gain of the amplifier circuit may be switched separately, and the distance signal may be generated from the two gains thus obtained.

Further, in the present embodiment, the level of the output signal of the integrating circuit is judged by the comparator, but another comparing means such as an analog / digital converter may be used.

Further, a switch for changing over the distance measuring mode is separately provided, and by operating the switch, the distance measuring operation as described in this embodiment and the distance measuring operation for obtaining a normal object distance are selected. You may make it possible to use it.

[0024]

According to the structure of the present invention, when amplifying an optical signal from a subject, preliminary light emission is performed to determine the gain of the amplifier circuit, and the subject distance is easily obtained from the gain to realize main light emission. Since the photographic lens is focused without entering, the process from the start of light projection to the focusing of the photographic lens can be performed extremely quickly, which is advantageous for a photo opportunity. Further, the number of times the light emitting element is driven is reduced, and the power consumption can be reduced.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is an operation diagram illustrating an integration operation according to the embodiment of this invention.

FIG. 3 is an amplifier circuit 40 and an amplifier circuit 50 according to an embodiment of the present invention.
6 is an operation diagram illustrating a method of determining the gain of FIG.

FIG. 4 is a table on a ROM 82 for obtaining a distance from values S1 and S2 according to the embodiment of the present invention.

FIG. 5 is a flowchart showing the operation of the embodiment of the present invention.

FIG. 6 is a flowchart showing a subroutine of a part for determining a value S1 in the flowchart of FIG.

FIG. 7 is a flowchart showing a subroutine of a part for determining a value S2 in the flowchart of FIG.

[Explanation of symbols]

 10 Light emitting circuit 3 PSD (light receiving element) 20 Current-voltage conversion circuit (far distance side) 30 Current-voltage conversion circuit (short distance side) 4 Switch 40 Amplification circuit 50 Amplification circuit 60 Integration circuit 70 Level determination circuit 80 CPU (calculation means) )

Claims (1)

[Claims] 1. A light projecting means for irradiating a subject with light, and a light projecting means for receiving light reflected by the subject.
A light receiving means for converting into one current, and a first current-voltage conversion circuit for converting one output current of the light receiving means into a voltage,
A second current-voltage conversion circuit for converting the other output current of the light-receiving means into a voltage, selection means for selecting an output of the first or second current-voltage conversion circuit, and an output signal selected by the selection means. An amplifying circuit for amplifying the output signal of the amplifying circuit, a integrating circuit for integrating the output signal of the amplifying circuit, comparing means for comparing the output signal of the integrating circuit with a predetermined signal, and A distance measuring device for a camera, comprising: a gain adjustment selecting means for adjusting a gain; and a computing means for obtaining a distance signal to a subject based on an adjustment result of the gain adjusting means.