JP3090150B2 - Active distance measurement method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-beam type active distance measuring method for projecting distance measuring light to a plurality of positions in a photographing screen and receiving the reflected light to measure the distance. .

[0002]

2. Description of the Related Art Active compact distance measuring devices are used in recent compact cameras. An active-type distance measuring device emits near-infrared light toward a subject and reflects reflected light from the subject using a semiconductor position detector (PSD: Position: PSD).
Light is received by a light-receiving element such as a Sensitive Detector. The incident position of the reflected light on the light receiving element changes according to the subject distance, and the signal from the light receiving element changes accordingly, so that the subject distance can be electrically measured. In such a distance measuring device, the light projecting unit for projecting the distance measuring light is a light source such as a near-infrared light emitting diode and a light projecting device for efficiently directing the distance measuring light from the light source toward the subject side. The light receiving unit includes a light receiving lens for efficiently collecting the reflected light from the subject on the light receiving element, in addition to the light receiving element.

The PSD which is frequently used as the light receiving element is 2
There are two output terminals, and a current corresponding to the position and intensity of the incident light is generated from each output terminal. Then, a signal depending only on the incident position of light can be obtained by obtaining the current of these two channels or the ratio of the voltage proportional to these. When such a PSD is used as the light receiving element of the distance measuring device, the intensity of the reflected light from the subject changes depending on the subject distance.
One output signal may be too large or too small. In such a case, the measurement accuracy cannot be stably maintained even if the ratio of the two output signals is taken. Therefore, in order to keep the levels of the two signals from the PSD within an appropriate range, a gain control amplifier is connected to each channel, feedback is provided to the gain control amplifier, and the gain is automatically adjusted so that the distance measurement accuracy based on the subject distance is obtained. I try to eliminate the variation.

Some of the above-mentioned active distance measuring devices include:
There is a multi-beam type in which distance measuring light is projected not only at a central portion in a shooting screen but also at a plurality of peripheral portions thereof, and a subject distance is measured at the plurality of distance measuring points. According to this, even when the main subject is displaced from the center of the photographing screen, it is possible to project the distance measuring light to this and obtain the distance signal. After obtaining the distance signal for each distance measuring point in this way, for example, by performing processing such as selecting the one corresponding to the closest subject distance and performing focusing, a simple operation with a high probability is performed. A photograph in which the main subject is in focus can be taken.

When the above-described multi-beam type active distance measuring apparatus is employed, a plurality of distance signals can be obtained from within the photographing screen, and in some cases, focusing is performed using distance signals obtained from the peripheral portion of the photographing screen. Therefore, it is necessary to detect a distance signal as accurate as possible from each ranging point. For this reason, various measures have been taken, such as projecting distance measurement light a plurality of times at each distance measurement point to obtain a plurality of measurement data, and calculating a distance signal from an average value of the measurement data. Also, if the measurement data is detected many times from a plurality of ranging points, the time required for ranging becomes longer, so the measurement data is read from the ranging point in the center of the shooting screen where the probability of the existence of the main subject is high. As for the number of times, a method of reducing the number of times measurement data is read may be used for a distance measuring point set in a peripheral portion of a shooting screen.

[0006]

By the way, a projection light used for projecting distance measuring light to a plurality of distance measuring points set in a photographing screen and collecting these reflected lights on a light receiving element. Both the lens and the light receiving lens are commonly used for each distance measuring point due to the demand for compact and low cost cameras. For this reason, efficient light projection and light reception can be performed at the distance measurement point at the center of the shooting screen, while distance measurement light from the light source or the distance measurement point at the periphery of the shooting screen can be obtained. The reflected light from the lens is obliquely incident on the lens. Therefore, the signal amount of the measurement data detected from the distance measuring points in the peripheral portion of the photographing screen becomes small because the peripheral light amount of the light projecting lens or the light receiving lens decreases.
For this reason, if the signal amount becomes too small, the gain of the gain control amplifier described above is automatically adjusted to the larger one, and even if the subject distance is the same, measurement data is obtained from ranging points around the shooting screen. In many cases, the gain is larger when obtaining the measurement data from the ranging point at the center of the shooting screen.

However, when the gain of the gain control amplifier increases, the noise component included in the measurement data also increases, and the reliability of the measurement data decreases. Moreover, in order to shorten the distance measurement time, if the number of times of distance measurement at the periphery of the shooting screen was reduced from that at the time of distance measurement at the center of the shooting screen and the average was taken, the periphery of the shooting screen was originally measured. The measured data at the time tends to vary. Therefore, if the gain when measuring the distance to the periphery of the shooting screen tends to be set to be larger than the gain when measuring the distance to the center of the shooting screen, the measurement from the center of the shooting screen where the probability of the existence of the main subject is high is high. The influence of the measurement data from the periphery of the photographing screen on which the noise component is more likely to be superimposed than the data is strengthened, which is a major cause of erroneous distance measurement.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and a multi-beam type active distance measuring device in which erroneous distance measurement is prevented from being caused by a distance signal obtained from a peripheral portion of a photographing screen, which is likely to vary. The aim is to provide a method.

[0009]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a ratio of output signals obtained from a pair of output terminals.
A light-receiving element whose incident position of light can be identified by
Output signals from each pair of output terminals
With a gain control amplifier that amplifies individually
Each distance measurement set at the center and periphery of the shooting screen
The distance measurement light is projected several times to each point, and the reflected light
The light is received by the light receiving element through a light receiving lens, and the gain
Output signal obtained through the control amplifier
The gain is adjusted so that it approaches
After performing the gain determination process to determine the
The distance is measured for each ranging point with the gain
Based on a pair of output signals from the control amplifier
To obtain a distance signal corresponding to the subject distance for each ranging point
In the gain determination process, the center of the shooting screen
Than the maximum gain that can be set for
Maximum gain that can be set for ranging points around the shadow screen
The value is kept low .

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1 schematically showing the structure of a distance measuring apparatus according to the present invention, a light projecting section 2 comprises a light source section 3 and a light projecting lens 4, and an optical axis 4a of the light projecting lens 4 is photographed. It is substantially parallel to the optical axis 5a of the lens 5. The light source unit 3 includes three LEDs (light emitting diodes) 3 each emitting near-infrared light.
a, 3b and 3c. These LEDs 3a, 3b,
3c are arranged horizontally, the central LED 3a is located on the optical axis 4a, and the LEDs 3b and 3c are located on the left and right sides, respectively. Beam-like ranging light is sequentially directed toward three places in the photographing screen. Emits light.

The light receiving section 7 comprises a light receiving lens 8 and a PSD 9, and the optical axis 8a of the light receiving lens 8 is
It is almost parallel to a. The PSD 9 outputs a signal corresponding to the amount of incident light and the incident position to each of the output terminals 9a and 9b.
Output from As is apparent from FIG. 1, the reflected light from the subject is incident on the terminal 9b side of the PSD 9 as the near subject is closer, but the ratio of the sum and difference of the ratio of the output signals from the output terminals 9a and 9b is higher. A signal corresponding to the incident position can be obtained without depending on the amount of incident light. Note that PSD 9 has no discriminating action in the horizontal direction, and if the incident height in the vertical direction is the same,
Output terminals 9a, 9b even if the incident position in the horizontal direction is different
Will be equivalent.

LEDs 3a to 3c are auto focus ICs
Light emission is controlled via a LED driver 11 by a signal from the LED driver 12. The autofocus IC 12 executes a predetermined distance measuring sequence according to a command from the microcomputer 14 and operates the LED driver 11 and amplifies and samples and holds each signal from the output terminals 9a and 9b of the PSD 9. The data is processed and output to the microcomputer 14. The microcomputer 14 performs a calculation based on the output signals of the first and second channels obtained as described above, and calculates a distance signal having a correlation with the subject distance. Then, the set position of the photographing lens 5 is determined according to the distance signal calculated by the microcomputer 14.

A general-purpose microcomputer is used as the microcomputer 14, and also receives photometric data detected by the photometric circuit 51 and digitally converted by the A / D converter 52.
The microcomputer 14 calculates the optimum exposure condition based on the photometric data, drives the stepping motor 54 via the exposure control circuit 53, and opens and closes the program shutter 55 at an aperture value and a shutter speed satisfying the optimum exposure condition. After photographing, the film feed motor 57 is driven by the film transfer circuit 56 to feed the film one frame. Before the program shutter 55 is opened and closed, the stepping motor 60 is driven by the lens moving circuit 58 at a rotation angle corresponding to the distance signal, and the photographing lens 5 is controlled to extend to the in-focus position.

The autofocus IC 12 and the microcomputer 14 are constructed as shown in FIG. The autofocus IC 12 is a one-chip IC, and includes a logic circuit 15, a gain controller 16, a preamplifier 17a for converting signal currents of the first and second channels output from output terminals 9a and 9b of the PSD 9 into voltages. 17b, gain control amplifier 18
a and 18b, sample and hold circuits 20a and 20b, buffer amplifiers 21a and 21b, and the like.

Gain control amplifiers 18a, 18b
Is provided in consideration that when the subject distance is long, the amount of reflected light incident on the PSD 9 decreases and the absolute value of the signal current from the output terminals 9a and 9b decreases. An appropriate amplification factor is given by a gain control process described later. Sample and hold circuit 20a,
20b receives the sampling pulse from the logic circuit 15, samples and holds the signals amplified by the gain control amplifiers 18a and 18b, and outputs these signals to the microcomputer 14 via the buffer amplifiers 21a and 21b. The logic circuit 15 basically comprises a serial-in / parallel-out shift register, and the gain controller 16 reads out gain control data set at a predetermined bit position of the shift register, and based on the read data, a gain control amplifier 18a. , 18b.

The microcomputer 14 has a CPU 2
4, a serial port 25, an A / D converter 26,
ROM 2 storing a program for executing a distance measuring sequence
7 and a RAM 28 for temporarily storing data and various flags obtained when the distance measurement sequence is executed. The serial port 25 converts a command from the CPU 24 into a serial data pulse (AFSD) and
5 and a serial data transfer pulse (AFSCK), serial data latch and LED3.
a to 3c control pulses (AF
LCK). Also, the A / D converter 26
The analog signal supplied from the auto focus IC 12 is converted into an 8-bit digital value (representing 0 to 255 in decimal) corresponding to the signal voltage level.

FIG. 3 conceptually shows an 8-bit serial-in / parallel-out shift register 30 used in the logic circuit 15. The gain control data (GAIN) is stored in the five bits D0 to D4.
LED light emission data (LED) is written in 2 bits of ~ D6,
In addition, LED light emission / reset switching data (SET) is set in one bit of D7. The 5-bit gain control data can represent gain levels from “0” level to “31” level. Also, 2
The bit LED emission data is “0”, “1”, “2”,
It can represent 4 states of “3”, and when “0”, L
Turn off all of ED3a ~ 3c, LED when "1"
Only 3a lights up, and when "2" and "3", LE respectively
D3b and LED3c are turned on.

FIG. 4 is a flow chart showing the basic procedure of the distance measuring sequence. The processing for detecting the offset value of the amplifier system of the autofocus IC 12 includes the LEDs 3a to 3c.
The output signal obtained by turning on in sequence is obtained through the gain control amplifier, and the gain determination process is performed to determine the gain of the gain control amplifier to the optimum value according to the signal level. The processing of taking in and performing a distance measurement operation based on the measurement data is sequentially executed.

The operation of the above configuration will be described below. When the distance measurement sequence is started by a half-press signal of the shutter button, first, the offset value detection processing shown in FIG. 5 is executed. When the offset value detection process is performed, “01000000” (binary number) is set in each bit position of “D0 to D7” of the shift register 30. Thereby, “GAIN = 8”, “LED =
0 "and" SET = 0 "are set. This command data is set at the time point P1 shown in the timing chart of FIG.
K sends eight pulses and is latched when the control pulse AFLCK goes low. The transfer of the serial data pulse is sequentially transferred to the shift register 30 at the rise of the transfer pulse AFSCK.
After the transfer of the command data, "COUNT = 8" is set in a predetermined register in the CPU 24.

Among the command data set in the shift register 30, the data of “GAIN = 8” is transmitted to the gain control amplifier 18 through the gain controller 16.
a, 18b and supplied to the gain control amplifier 18
The gains of a and 18b are each set to “8”. In addition,
“GAIN = 31” corresponds to the maximum gain, and “GAIN = 0” corresponds to the minimum gain.

After transferring the serial data, the output signals from the first and second channels are sampled and held, and
The digital values AFD1 and AFD2 obtained by the / D conversion are read into the microcomputer 14 as 8-bit binary data. As shown in the flowchart of FIG. 7, the procedure of the reading process is as follows.
It is set to low level during one period. When the serial data pulse AFSD changes during this period, the LEDs 3a to 3c and the sample and hold circuits 20a and 20a
Control such as b is performed. First, the time point of P2 when the AFSD becomes low level is used for the lighting timing of the LEDs 3a to 3c. However, at the time of the offset value detection processing, since the command is “LED = 0”, none of the LEDs 3a to 3c is turned on.

When ΔT2 elapses from the time point of P2, AFSD
Becomes high level, and at this timing, the sample-and-hold circuits 20a and 20b
a and 18b are held. Note that these output signals are output to the gain control amplifier 18.
a and 18b are the values amplified by the initial setting “GAIN8”. After a lapse of ΔT3, AF
SD becomes a low level and is used as a light emission stop signal of the LEDs 3a to 3c, and returns to a high level after ΔT4. AFLCK goes high again after the elapse of the low level period of ΔT1, and one cycle is completed after the elapse of the high level period ΔT5.

When a time ΔT6 has elapsed from the time point P3 when the AFSD becomes low level, the sample hold circuit 20
The output signals held by the A / D converters 26a and 20b are converted by an A / D converter 26 through buffer amplifiers 21a and 21b.
These are converted into digital values of bits, and these are converted as measurement data AFD1 and AFD2 of the first and second channels by the CPU.
24, and stored in a predetermined address position in the RAM 28.

The above-described processing for taking in the measurement data AFD1 and AFD2 is repeated eight times. Then, these eight measurement data are averaged for each channel, and the average value is determined as offset values OF1 and OF2. Since this offset value detection process is executed with the LEDs 3a to 3c turned off, the average value of these values is PS
This means a value due to noise due to ambient light incident on D9, noise generated by amplifiers after the preamplifiers 17a and 17b, and a signal processing system.

After the detection of the offset value, the gain determination processing shown in the flowcharts of FIGS. 8 and 9 is performed. When the gain determination process is started, the “GSNG flag” set in the RAM 28 is reset to an initial state, and “GCOUNT” is set to an initial value “0”.
Thereafter, the serial data representing the new command is transferred from the serial port 25 to the logic circuit 15, and “0100001” is stored in each bit position of the shift register 30.
The binary data of "1" is set. As a result, the gains of the gain control amplifiers 18a and 18b are set to the initial value “8”, and “LED = 1” and “SET =
Each command of "1" is set, and only the LED 3a is turned on.

As shown in FIG. 8, when the gain determination process is performed with the command setting of “LED = 1”, the maximum value “GMAX” of the settable gain becomes “31”,
When “LED = 2” or “LED = 3”, “G
MAX = 28 ". That is, for the distance measurement point P1 set at the center of the photographing screen 40 illustrated in FIG.
With respect to the maximum value of the gain when measuring the distance by lighting of the ED 3a, the distance measuring points P2 and P
The maximum value of the gain when measuring the distance of 3 is kept low.
The reason is that the reflected light from the distance measuring points P2 and P3 in the peripheral portion is originally obliquely incident on the light receiving lens 8 and the amount of light tends to decrease, and the gain is set too high to compensate for this. This is because the noise is also amplified and the measurement data tends to vary. Therefore, by lowering the maximum value of the gain when measuring the distance measuring points P2 and P3 in the peripheral portion of the photographing screen as described above,
The effect of noise on the obtained measurement data can be kept almost the same between when the distance is measured at the center of the shooting screen and when the distance is measured at the periphery of the shooting screen, and the distance measurement conditions are maintained uniformly. be able to.

After the command is set, the reading process of the measurement data AFD1 and AFD2 is executed in the same manner as the offset value detecting process. In this case, as is clear from the time chart of FIG.
It is lit during the period of "3". Therefore, in the state of FIG.
The distance measurement light from the ED 3a is applied to the main subject S1, and the reflected light enters the PSD 9 through the light receiving lens 8.
At this time, the signals output from the two terminals 9a and 9b of the PSD 9 include information on the intensity of light incident on the PSD 9 and the incident position. Moreover, each LED 3a-3
The lighting cycle of c is determined to be 1 msec.

When these signals are converted into digital data and then taken in as measurement data AFD1 and AFD2, it is determined whether or not any of them has reached "F0" in hexadecimal ("240" in decimal). Is done. If any of them is equal to or more than “F0”, it is determined that the level is too high and almost overflows (saturates). The fact that one of the measurement data has reached the saturated state means that the amount of light incident on the PSD 9 is extremely large and the measurement data lacks reliability. This is a case where the reflected light is too strong even at the minimum gain of “GAIN = 8” at a close position. Therefore, when it is confirmed that the gain value at this time is the initial value (minimum value) “8”, “AFRESULT ← 127” (“AFRESUL
T ”, which will be described later).
A distance signal is obtained for moving the camera to a close distance at which shooting is possible, and the distance measurement by the LED 3a ends at this point.

When it is detected that an overflow condition has occurred and the gain value at this time is "9" or more, the GSNG flag is set after confirming that the overflow has not occurred immediately before. Then, after a time delay of 2 msec, reading of the measurement data AFD1 and AFD2 is executed again with the same gain value. And
Similarly, when an overflow is recognized, the gain value is determined by subtracting “1” from the gain value at that time, the gain determination process is stopped, and the process directly proceeds to the distance measurement sequence. Thus, it is possible to prevent the gain determination processing from being lengthened due to the repeated overflow.

The measurement data AFD is again measured with the same gain.
1, when taking in AFD2, 2 msec
A time delay of c is performed. For example, if the timing of the intermittent lighting by the fluorescent lamp coincides with the reading timing of the measurement data AFD1 and AFD2, an overflow occurs in the outputs of the gain control amplifiers 18a and 18b, and thereafter, the gain control amplifiers 18a and 18a for about 2 msec. The gain of 18b becomes unstable.
Therefore, at least during that time, the measurement data AFD1,
Since it is more advantageous to wait for reading of the AFD 2 to obtain accurate measurement data, the delay processing of 2 msec is performed as described above. Of course, the delay time may be appropriately set in the range of about 1 to 5 msec according to the noise control characteristics of the gain control amplifiers 18a and 18b.

It is also possible to set the minimum value of the above gain to "8" or less.
Can be determined as appropriate according to the amount of light. It should be noted that an overflow is recognized in one of the measurement data ADF1 and AFD2, and a state in which the gain value is not “8” does not occur at the beginning of the gain determination process, but occurs in an iterative routine described later.

If no overflow is observed in the measurement data AFD1 and AFD2 when the gain is at the initial value "8", the addition measurement data AFADD and the subtraction measurement data AFDIF shown in FIG.
Is calculated. In this processing, the offset values OF1 and OF2 are subtracted from the measurement data AFD1 and AFD2 to remove noise components. With respect to the addition measurement data AFADD calculated in this way, it is determined whether or not the value is greater than or equal to decimal “136”. When this value is “136” or more, the additional measurement data A
It is determined that the values of FD1 and AFD2 are at a level appropriate for the subsequent execution of the distance measurement calculation. Then, the gain of the gain control amplifiers 18a and 18b is determined by the “GAI” at that time.
N ”(initial value“ 8 ”) and subsequently LE
The distance measurement processing by D3a is executed. In addition,
When the result of the offset value subtraction processing becomes a negative value or when the value of the subtraction measurement data AFDIF becomes a negative value, these values may be set to “0” to simplify the subsequent calculation. it can.

On the other hand, if the value of the additional measurement data AFADD is less than "136", the level of the additional distance measurement data AFADD is too low in consideration of performing the subsequent distance measurement calculation, that is, the initial gain. “8” means that the level of the measurement data AFD1 and AFD2 is low. At this time, the measurement data AFD1, A
To increase the absolute value of FD2, “N” is added to the value of “GAIN”. The value of "N" added in this way is
The values are set as shown in the following table according to the size of the added measurement data AFADD at that time.

[0034]

[Table 1]

In the process of changing the value of “GAIN”, the command is set again.
Only the data at the bit positions of "0" to "D4" change, and the data at the other bit positions remain unchanged. Then, the gain controller 16 controls the gain control amplifiers 18a and 18b according to the new value of “GAIN”.
Is adjusted, and “GCOUNT” representing the frequency of the gain determination processing is increased by “1”, and the same processing is repeated. During the repetition processing, an overflow may occur when “GAIN> 8”. However, when the “GSNG flag” is in the set state, the gain is determined by “GAIN ← GAIN−1” and the distance measurement processing is executed.

According to the above, when the measured data AFD1 and AFD2 overflow when the gain control amplifiers 18a and 18b have the initial gain of "8", the distance signal is immediately determined to a value corresponding to the close distance. Even if no overflow occurs, the additional measurement data AFAD
When D is at an appropriate level, the distance measurement processing is executed with the gains of the gain control amplifiers 18a and 18b set to the initial gain "8". Thus, "GCOUN
When the value of "T" is not more than "1", that is, when the gain of the gain controls 18a and 18b is small, the influence of noise is small. Therefore, it is advantageous to determine the gain earlier and perform the distance measurement process.

When “GCOUNT ≧ 2” is established during the repetition routine of the gain determination and the gain value is set to a high value, as shown in FIG. 9, “GCOUNT =
6 ”, the measurement data AFD1 and AFD2 are detected. These measurement data are“ SUM1 ”and“ SU ”.
M2 ". And "GCO
When “UNT = 6” is reached, the accumulated “SUM1”,
Measurement data AFD of each channel from "SUM2"
The average value is calculated after subtracting the maximum value of AFD1 and AFD2, and is replaced with “AFD1” and “AFD2”, respectively.

The measurement data AFD1, A thus obtained
As for FD2, as shown in FIG. 10, after offset correction processing, addition measurement data AFADD and subtraction measurement data AFDIF are calculated. Then, “AFADD ≧
If “136” is satisfied, the flow shifts to distance measurement processing.
“AFADD ≧ 136” is not satisfied, and the gain of the gain control amplifiers 18a and 18b is set to the maximum value “3”.
1 ”(however, when the LED 3a is turned on), it means that the subject is located at a long distance where reflected light hardly enters the PSD 9, so the photographing lens 5 is set to infinity. Distance signal "AFRE
SULT = 0 ”is obtained, and the distance measurement by the LED 3a ends at this time.

At the time of the gain determination processing while turning on the LEDs 3b and 3c, the value of "GMAX" is set to a low value of "28". Therefore, when the additional measurement data AFADD of a predetermined level or more cannot be obtained, the AF points of the peripheral distance measuring points P2 and P3 shown in FIG. 13 are set to "AFRESULT" earlier than the central distance measuring point P1. As "= 0", a distance signal corresponding to infinity is determined. The reason is that, regarding the distance measurement points P2 and P3 set in the peripheral portion of the photographing screen 40, even if the gain is increased to some extent, “AFADD ≧ 1”
If “36” is not satisfied, it is highly probable that the main subject is not located there and is at infinity, and the gain value at that time is set to “GAIN =
This is because it does not make much sense to increase the number to "31". In addition, the reflected light from the peripheral portion of the photographing screen enters the light receiving lens 8 as obliquely incident light, and the signal level is reduced due to the influence of the decrease in the peripheral light amount of the light receiving lens 8, and the gain tends to be naturally set to be high. But the gain value is
When the value is increased to "IN = 31", the noise is also amplified and the possibility that even signals unrelated to the main subject are read as measurement data from the main subject increases. In particular, when the measurement data for the distance measurement calculation is acquired a plurality of times for each of the distance measurement points after the gain determination processing, the number of times of reading the measurement data from the distance measurement points P2 and P2 in the peripheral portion of the shooting screen is increased. When the distance signal is set to be smaller than the distance point P1 (details will be described later), the distance signal obtained by averaging the measurement data from the peripheral portion has more variation than the distance signal obtained at the central portion. Considering that it is easy to come out, when determining the gain for the LEDs 3b and 3c as described above, “GMAX” is set low and “GAIN> GM
Determining the distance signal early by "AX" is effective not only for shortening the distance measurement time but also for preventing erroneous distance measurement.

Gain control amplifiers 18a, 18b
When setting the gain of the measurement data AFD high,
By fetching a plurality of AFDs 1 and AFD2 and determining the gain in consideration of their average value, the gain can be set almost without being affected by noise. When calculating the average value from the integrated values SUM1 and SUM2 of the measurement data AFD1 and AFD2, the maximum value of the AFD1 and AFD2 is subtracted. Therefore, even if the measurement data AFD1 and AFD2 are captured under the illumination of a fluorescent lamp and a periodic noise component is superimposed on the measurement data AFD1 and AFD2, such abnormal data should be removed when calculating the average value. This is very effective in setting an appropriate gain.

When the value of "GAIN" is determined by the above processing, the gain control amplifiers 18a and 18b
LED3a continues with the gain set to that value.
Is performed. FIG. 11 and FIG. 12 show this distance measurement processing procedure. In the distance measurement process by the LED 3a, the LED 3a is turned on 64 times at a time interval of 1 msec, and the AFD1 and the AFD2 are read each time. And every AFD1, A
At the time of reading the FD2, it is determined whether any of them overflows or whether the value is less than “15” and is insufficient as the absolute value of the measurement data,
When applicable, "OVC" indicates that the distance measurement is inappropriate.
COUNT ”is incremented by“ 1 ”.

As shown in FIG. 11, "LED = 1", that is, at the time of distance measurement by the LED 3a, 64 light projections and reading of the measurement data AFD1 and AFD2 are performed, and the number of repetitions is "LED = 2, 3". , Ie LED3
The number of repetitions by b and 3c is determined to be 32 times. As a result, the distance measurement points P2 and P
On the other hand, at the distance measuring point P1 at the center of the shooting screen where the main subject is likely to be located, double measurement data can be captured, which is advantageous in maintaining stable accuracy and relatively low in importance. The distance measurement time at the peripheral portion of the screen can be reduced. Also, “OVCOUNT” represents the upper limit of “OVCOUNT”.
VMAX ”is also“ 16 ”,
At the time of distance measurement by the LEDs 3b and 3c, "8" is determined.

During the distance measurement by the LED 3a, "OVCOU" is displayed.
When "NT" is less than "16", the gain value is kept as it is for confirmation, and after a delay time of 2 msec, the measurement data AFD1 and AFD2 are read again. Accordingly, even if reading of the measurement data AFD1 and AFD2 coincides with the lighting timing of the fluorescent lamp and overflow occurs in the measurement data, correct measurement data can be obtained in the next reading. "OVCOUNT" changes to "O
When “VMAX = 16” is reached, it is determined that the gain value determined in the gain determination processing is inappropriate, and “OFLAG”
Is set to “1”, “GAIN” is reset to “1” lower, and the distance measurement process is restarted from the beginning. In addition, in order to prevent the distance measurement process from being repeated many times, once "O
After “VFLAG” is set to “1”, “OV
When "COUNT" reaches "16", the value of "AFRESULT" is determined as "M" corresponding to the value of "GAIN" at that time. At the time of this determination, the following table is referred to.

[0044]

[Table 2]

As described above, when the value of "OVERCOUNT" is less than "16", the distance measurement is continued with the same gain. However, since the maximum value and the minimum value in the measurement data AFD1 and AFD2 are removed and a plurality of measurement data are averaged in the subsequent processing, abnormal data due to about two overflows is included in the measurement data. However, the influence hardly appears in the distance measurement calculation.

In this way, 64 measurement data AFD
In the process of taking in AFD1 and AFD2, AFD1 and ADF2 are summed up as "SUM1" and "SUM2", respectively, after identifying the minimum value and the maximum value among them. Then, after subtracting the maximum value and the minimum value of each of AFD1 and AFD2 from these total values "SUM1" and "SUM2", the average value is calculated. Although the maximum value and the minimum value are subtracted in order to improve the reliability of the average value, the subtraction may be omitted.

The average value obtained for each channel is newly updated as the averaged measurement data AFD1 and AFD2. After the offset value is corrected according to the processing of FIG. 10, the addition measurement data ADADD and the subtraction measurement data AFD are obtained.
Converted to IF. Then, “12” is added to the value of these ratios.
8 ”to calculate a distance signal“ AFRESULT ”,
The distance measurement process using the LED 3a ends.

Subsequently, the gain determination processing-distance measurement processing while the LED 3b is turned on, and the gain determination processing-distance measurement processing while the LED 3c is turned on are repeated.
The value of the distance signal “AFRESULT” for each of 3b and 3c is obtained. Since the measurement data AFD1 and AFD2 are read 32 times by turning on the LEDs 3b and 3c, the reading of the measurement data is completed in a shorter time than when the LED 3a is turned on. The 32 measurement data AFD1 and AFD2 thus read are averaged after the subtraction of the maximum value and the minimum value by the processing shown in FIG.
By the processing shown in FIG. 10, the added measurement data AFADD,
Subtraction measurement data AFDIF is determined. Then, from these values, the distance signal “A” for each of the LEDs 3b and 3c
FRESULT ”is calculated.

The value of the distance signal “AFRESULT” is L
The value corresponds to the subject distance obtained for each distance measurement in the EDs 3a to 3c. If the distance signal from the LED 3a is "AFRESULTa", the distance signal from the LED 3b is "AFRESULTb", and the distance signal from the LED 3b is "AFRESULTc", FIG. 1 or FIG.
In the subject arrangement shown in (1), "AFRESULTa" indicates a value corresponding to the distance to the main subject S1, "AFRESULTb" indicates a value corresponding to the distance to the background subject S2, and "AFRESULTc" indicates that the ranging light is not reflected. To “0” (see FIG. 8). In such a case, the microcomputer 14 checks whether “AFRESULTa” is a value corresponding to the subject distance from the closest distance to 5 m in accordance with the program stored in the ROM 27, and if this is the case, “AFRESULTa”.
Ta ”is determined as the optimal distance signal, and if not applicable,“ AFRESULTa ”,“ AFRESULT ”
b) and AFRESULTc, the distance signal corresponding to the closest subject distance is determined as the optimum distance signal, and the distance measurement sequence is completed.

After the optimum distance signal is determined in this way,
The stepping motor 60 is driven via the lens moving circuit 58, and the photographing lens 5 is moved to a focus position corresponding to the distance signal. “AFRESULTa”,
As the algorithm for determining the optimal distance signal from “AFRESULTb” and “AFRESULTc”, various other algorithms can be selected.

The embodiment has been described in which three LEDs 3a, 3b, and 3c are used to sequentially measure distances at three locations in a photographing screen. In the present invention, light is projected to the center of the photographing screen. L projected on the periphery of the shooting screen in addition to the LEDs
The present invention can also be applied to a case where three or more EDs are used, or a case where the distance measuring light is projected and measurement data is read once or at the same plural times for each distance measuring point. In addition, the present invention can be applied to a system in which an LED or a light projecting lens is movable, and one of the light emitting devices emits distance measuring light from one LED to a plurality of distance measuring points while moving either of them. is there. Further, in practicing the present invention, it is possible to omit the offset value detection processing or partially change the distance measurement processing procedure, and to use a light receiving element other than the PSD, such as a CCD image sensor, for example. Alternatively, various controls may be performed by a logic circuit other than the microcomputer.

[0052]

As described above in detail, according to the distance measuring method of the present invention, each of the distance measuring methods set at the central portion and the peripheral portion in the photographing screen.
The distance measurement light is projected at the distance measurement points, and a distance signal is obtained for each distance measurement point.
Before performing distance processing, a pair of output terminals of the light receiving element
Gay to amplify the resulting output signals with equal gain
Control amplifier to adjust the gain of the control amplifier for each AF point.
In decision processing is performed. And this gain decision processing
Can be set for the distance measurement point in the center of the shooting screen.
Of the focus point around the shooting screen
So that the maximum gain that can be set
Output signal when measuring the distance around the screen is noisy.
Is amplified too much with the
This is very effective in preventing erroneous multi-beam ranging from being performed.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a distance measuring device used in a distance measuring method of the present invention.

FIG. 2 is a block diagram illustrating a configuration of an autofocus IC.

FIG. 3 is a conceptual diagram of a shift register used in a logic circuit.

FIG. 4 is a flowchart showing an entire ranging sequence.

FIG. 5 is a flowchart illustrating a processing procedure of offset value detection.

FIG. 6 is a time chart for explaining reading timing of measurement data.

FIG. 7 is a flowchart showing a procedure for reading measurement data.

FIG. 8 is a flowchart showing a part of a processing procedure for determining a gain.

FIG. 9 is a flowchart illustrating a part of a processing procedure for determining a gain.

FIG. 10 is a flowchart illustrating a calculation processing procedure of addition measurement data and subtraction measurement data.

FIG. 11 is a flowchart illustrating a part of a distance measurement processing procedure.

FIG. 12 is a flowchart illustrating a part of a distance measurement processing procedure.

FIG. 13 is an explanatory diagram illustrating an example of a shooting screen.

[Explanation of symbols]

 2 Emitter 7 Light receiver 9 PSD 12 Autofocus IC 14 Microcomputer 15 Logic circuit 16 Gain controller 18, 18b Gain control amplifier

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shigenken Goto 1-324 Uetake-cho, Omiya City, Saitama Prefecture Inside Fuji Photo Optical Co., Ltd. (72) Tatsuo Saito 1-324 Uetake-cho, Omiya City, Saitama Prefecture (56) References JP-A-1-288715 (JP, A) JP-A-63-266434 (JP, A)

Claims (1)

(57) [Claims] 1. An output signal obtained from a pair of output terminals.
A light receiving element capable of identifying a light incident position by a ratio,
Output signals from each of a pair of output terminals are equal to each other
Gain control amplifier that amplifies individually with gain
Used, received by the light receiving element through the central portion and each of the distance measuring point of each set to the peripheral portion and projecting distance measuring light by a plurality of times receiving lens the reflected light of the imaging screen, the gain
The output signal obtained through the control amplifier is
Adjust the gain so that it approaches the bell.
After performing the gain determination process to determine the
The distance is measured for each ranging point with the gain
In the active distance measuring method in which a distance signal corresponding to a subject distance is obtained for each distance measuring point based on a pair of output signals obtained from a control amplifier, a distance measurement in a center portion of a shooting screen is performed in the gain determination processing. To a point
Than the maximum gain that can be set
An active distance measuring method, wherein a maximum value of a gain that can be set for a distance measuring point of a section is reduced.