JPS61246712A - Automatic focus adjuster - Google Patents

Abstract

PURPOSE:To detect a reflected light level from an object under a high S/N ratio and to improve focusing accuracy by selectively outputting a larger output out of outputs of two photodetecting elements to control the gain of an adjusting circuit. CONSTITUTION:When a light beam projected from a light projecting means 11 is reflected by an object 10 and made incident on photodetecting parts 12a, 12b of a photodetecting means 12, an automatic focus adjusting signal is detected from the adjusting circuit 13 by an output signal based on a difference between incident light values. Said signal is used for power supply etc. to a lens driving motor for driving a photographing lens to a focusing position. When a larger output out of the output signals of the photodetecting parts 12a, 12b is detected by a priority detecting circuit 14 and led into a gain adjusting circuit 15, the gain of the circuit 13 is adjusted by the output of the circuit 15. Even when the object 10 is located on a far position and the incident light of the reflected beams is low, only the larger output signal out of the outputs of the photodetecting parts 12a, 12b is selected and the gain is adjusted on the basis of the output signal having a high S/N ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an automatic focus adjustment device, and more particularly, to an automatic focus adjustment device used in optical devices such as film cameras and TV cameras.

[Conventional technology]

One type of automatic focusing device employs a method called an active method. This active method is
Of the light emitted from the camera to the subject, it receives the light that is reflected back from the subject and measures the distance. In this case, the principle of triangulation is generally used as the distance measuring means.

FIG. 2 is a principle diagram showing an example of the configuration of an optical system of an active automatic focusing device using the principle of triangulation.

When a beam of light such as infrared light emitted from the light emitting element 1 is irradiated by the focusing lens 2 toward the subject 3 in parallel to the optical axis direction of the photographing lens 5, the reflected light from the subject 3 is reflected from the photographing lens 5. a two-part light receiving element 4a installed off the optical axis;
4b.

The difference between the outputs of the two divided light receiving elements 4a and 4b is detected, for example, by a differential amplifier, and the direction and amount of movement of the photographing lens 5 are determined by the difference output, and the scum drive motor is driven in the forward and reverse directions. Rotate. Due to the rotation of this motor, the lens barrel of the photographing lens 5 moves in the optical axis direction while rotating around the optical axis. The two-split light receiving elements 4a and 4b are the photographing lens 5.
The inclination angle θ is changed in conjunction with the movement of the light receiving elements 4a and 4b, and the light receiving elements 4a and 4b rotate in a direction in which the difference output becomes zero.

Then, when the differential output between the light receiving elements 4a and 4b becomes zero, the photographing lens 5 becomes in focus. In the focused state, there is a difference between the tilt angle θ of the light receiving elements 4a and 4b, the distance between the optical axis of the photographic lens 5 and the two-part light receiving elements 4a and 4b, and the distance S from the photographic lens 5 to the subject 3. for.

The formula θ=tan7'' (S/D) is satisfied. Also, the above two light receiving elements 4a,
When the difference output of 4b is obtained, not only the focal joint venture but also
It is also possible to determine the directionality of the out-of-focus state when out of focus, that is, the state of front focus and back focus.

[Problem that the invention seeks to solve]

By the way, in general, in the automatic focus adjustment device as described above, the light receiving element 4 is adjusted depending on whether the subject is far or near, or when the reflectance differs depending on the subject.
A and 4b have the disadvantage that the output fluctuates significantly due to fluctuations in the amount of incident light, and as a result, the operation of the automatic focus adjustment device becomes extremely unstable. Therefore, the outputs of the two light receiving elements 4a and 4b are added, and the sum of the outputs of the two light receiving elements 4a and 4b is
An automatic focus adjustment device has also been proposed (Japanese Patent Publication No. 13012/1983) in which the gain of an adjustment circuit, which is a control system, of a lens drive motor is controlled by the output of the lens drive motor. If the output level of one of the photodetectors decreases in the focused state, the output level of the photodetector added above will also decrease, resulting in dark current deterioration. Even if the adjustment circuit is controlled, there are problems such as extremely low focusing accuracy. The present invention has been made in view of these problems, and it selectively outputs the larger output of the two light-receiving elements 4a and 4b, and uses the same output for driving multiple lenses. The purpose is to control the gain in the adjustment circuit that is the control system of the motor.

[Means for solving problems]

As shown in FIG. 1, this automatic focus adjustment device includes a light projection unit 11 that projects a light beam toward a subject 10, and two light receiving units 12a and 12 that receive the reflected beam from the subject 10.
A light receiving means 12 that receives light by b, and this light receiving section 12a
, an adjustment circuit 13 that obtains an automatic focus adjustment signal based on the difference in the amount of light incident on 12b, and the two light receiving sections 12a, 12.
a priority detection circuit 14 that selectively outputs the larger of both outputs upon receiving the output of b; and this priority detection circuit 14.
The gain adjustment circuit 15 adjusts the gain in the adjustment circuit 13 according to the output of the gain adjustment circuit 15.

[Effect]

In this automatic focus adjustment device, when the light beam projected by the light projection means 11 is reflected by the subject 1o and enters the two light receiving sections 12a and 12b of the light receiving means 12, the two light receiving sections 12a and 12b are divided based on the difference in the amount of incident light. An automatic focus adjustment signal is detected from the adjustment circuit 13 based on the output signal of. This automatic focus adjustment signal is used, for example, to supply power to a lens drive motor that drives the photographic lens to the in-focus position. Then, among the output signals of the two light receiving sections 12a and 12b, the larger output signal is detected by the priority detection circuit 14, and when this detection signal is guided to the gain adjustment circuit 15,
The gain in the gain adjustment circuit 13 is adjusted by the output of the gain adjustment circuit 15. However, even if the subject 1o is far away or the reflectance of the subject 100 is low, and the amount of incident light of the reflected beam is weak, the priority detection circuit 14 still detects one of the outputs of the two light receiving sections 12a and 12b. Only the larger output signal is selected, and gain adjustment is performed based on the good output signal of this chisel, thereby performing stable automatic focusing operation.

〔Example〕

Hereinafter, the present invention will be further explained based on Examples.

FIG. 3 is an electrical circuit diagram of an automatic grading device showing one embodiment of the present invention. The infrared light emitting diode 24, which is the light projection means 11, emits infrared light intermittently to save power consumption while receiving the oscillation pulse output of a constant frequency from the oscillator (hereinafter referred to as OSC) 21. It has become.

The two light-receiving elements 25a and 25b, which are the two light-receiving parts 12a and 12b of the light-receiving means 12, are connected between the input terminals of the front-stage amplifiers 26 and 27 and the ground, respectively, and are connected between the input terminals of the front-stage amplifiers 26 and 27, respectively, and the ground, so that the light emitted from the light-emitting diode 24 and reflected by the photographic object is detected. When receiving infrared light, each photocurrent Ia.

Amplified output signals corresponding to IbK are output from the front stage amplifiers 26 and 27, respectively. The outputs of the preamplifiers 26 and 27 are led to a differential output detector 29.
A signal corresponding to the output difference between the two front-stage amplifiers 26 and 27 is guided to the synchronous detector 3o. The synchronous detector 30 samples and holds the output of the differential output detector 29 using a constant frequency pulse generated by the OSC 21, and uses it as an automatic focusing signal. Therefore.

The relationship between the photocurrent Ia and the photocurrent Ib of the light receiving element 25a is as follows.

When Ia>Ib, the output level of the synchronous detector 3o is positive, and when Ia (Ib), the output level of the synchronous detector 3o is positive.
The output level of 0 is not negative, and when Ia=Ib, the output level of the synchronous detector 3o becomes equal to O1, that is, the ground level.

The output of the synchronous detector 30 is led to a current amplifier 32 through a gain switching circuit 31, where the current is amplified. Since a lens drive motor 33 for driving a photographing lens is connected between the output terminal of the current amplifier 32 and the ground, when the output level of the synchronous detector 30 is N positive, the photocurrent is 1. When the output level of the synchronous detector 30 is negative, the motor 33 rotates in the direction of increasing the photocurrent Ia and decreasing the photocurrent Ib. rotates in the opposite direction. When the output level of the synchronous detector 3o is 0, the potentials between both terminals of the motor 33 become equal, and the motor 33 stops rotating.

At this time, the photocurrent Ia=Ib.

In the gain switching circuit 31-, the electronic switch 34
The contact 34a is connected to the output end of the synchronous detector 30, and the contact 34a is connected to the connection point between voltage dividing resistors 35 and 36 connected in series between the output end of the synchronous detector 30 and ground. The movable contact piece of the electronic switch 34 is connected to the contact 34a side or the contact 34b side based on the output of a priority detection circuit 38, which will be described later. When the electronic switch 34 is connected to the contact 34a side, the output of the synchronous detector 30 is guided to the current amplifier 32 without attenuation, and the electronic switch 34 is connected to the contact 34a side.
4b side, the output of the synchronous detector 30 is divided by the resistance ratio of the resistors 35 and 36 and is led to the current amplifier 32 at an attenuated level.

Further, the outputs of the pre-stage amplifiers 26 and 27 are led to a priority detection circuit 38. This priority detection circuit 38 includes capacitors 39 and 39 at the output terminals of the pre-stage amplifiers 26 and 27, respectively.
NPN') transistors 41 and 42 are connected through the transistors 41 and 40, respectively, and the connection point of the voltage dividing resistor 43 and 44 connected in series between the application terminal of the power supply voltage Vcc and the ground is connected to the terminal of the transistors 41 and 42. It is connected to the connection point between resistors 45 and 46 connected in series between both bases, and has its emitter grounded via a common resistor 47 to the collector source voltage +Vcc application terminal of the transistors 41 and 42. ing. The emitters of the transistors 41 and 42 are connected as output terminals of the priority detection circuit 38 to the input terminal of a band pass filter (hereinafter referred to as BPF) 48.

In this priority detection circuit 38, the front stage amplifier 26°27
The influence of DC voltage variations on the surface output is removed by capacitors 39 and 40, and only the modulation component of the surface output is guided to transistors 41 and 42 (7), respectively. Resistors 43-4 are connected to the transistors 41 and 42.
6 provides a bias voltage.

When the light is in an out-of-focus state, the photocurrents 1a and Ib of the light receiving elements 25a and 25b become unbalanced. for example,
If I a > I b, the capacitor 39
, 40 to the transistors 41, 42, the outputs SA, SR of the preamplifiers 26, 27 have modulation component voltages EA, EB (EA>EB), respectively, based on the voltage Eb, as shown in FIG. Therefore, current flows through the pace-emitter of transistor 41 and resistor 47 due to this larger modulation component voltage EA. The reference voltage Eb during non-emission in intermittent light emission is determined by the resistors 43 and 44, and the resistor 45
, 46 are applied to the bases of the transistors 41 and 42 (D), and the pace potentials of the transistors 41 and 42 are the same.At this time, regarding the modulation component voltage EB, a reverse voltage is applied between the base and the emitter of the transistor 42. As a result, no current flows to the emitter of the transistor 42. As a result, the output Sc of the priority detection circuit 38 is output to the emitter side of the transistors 41 and 42.
As shown in FIG. 4, the signal SA of the larger modulation component voltage EA is preferentially detected. Similarly, when Ia (Ib), the signal SB of the modulation component voltage EB is detected from the priority detection circuit 38. Also, when Ia=Ib, either the signal SA or SR is Detected.

In this way, in the priority detection circuit 38, the smaller output among the outputs of the two light receiving elements 25a and 25b is cut off, and only the larger output is selectively detected. The influence of the dark current of the light receiving elements 25a and 25b is suppressed as low as possible, and therefore the output Sc of the priority detection circuit 38 is S/
N good signals will be obtained.

The signal Sc preferentially detected by the priority detection circuit 38 is then shaped into a substantially sinusoidal waveform by passing through the B P
It is sampled and held at the timing of a constant frequency pulse output from C21. The DC voltage output from this synchronous detector 49 is then applied to the gain switching circuit 31.
and one input terminal of a comparator 50 forming a circuit corresponding to the gain adjustment circuit 15. Therefore, in this comparator 5o, the level of the one input terminal and the power supply voltage +VCC of the other terminal are input. A comparison is made with the level of the input terminal connected to the connection point of resistors 51 and 52 connected in series between the terminal and ground. The comparator 5o is the synchronous detector 49
When the output level exceeds the reference level determined by the voltage division ratio between the resistors 51 and 52, a high level output is generated, and when it falls below the reference level, a low level output is generated. The electronic switch 34 of the gain switching circuit 31 is controlled to switch according to the output level of the comparator 50, and the electronic switch 34 is connected to the contact 34b side when the output of the comparator 50 is at a high level. and comparator 5
When the output of 0 is at a low level, the contact 34b side is connected.

t9. When the amount of light incident on the light receiving elements 25a and 25b increases, such as when the subject is nearby or when the reflectance of the subject is high, the shimiko switch 34 is connected to the contact 34bi according to the output of the comparator 50. As a result, the output of the synchronous detector 30 is guided to the current amplifier 32 at a value attenuated by the resistors 35 and 36, so that at this time, the lens drive control operation of the motor 33 described above is performed with low sensitivity. Also.

Conversely, when the amount of light incident on the light receiving elements 25a and 25b decreases, such as when the subject is far away or when the reflectance of the subject is low, the output of the comparator 50 causes the shim switch 34 to switch to the contact 34a side. Connect to synchronous detector 3
Since the zero output is directly guided to the current amplifier 32 without attenuation, the lens drive control operation of the motor 33 is performed with high sensitivity at this time. By providing the priority detection circuit 38, as already mentioned, the light receiving element 25a.

Even if the amount of light incident on the light receiving element 25b decreases, only the larger one of the two light receiving elements 25a and 25b is detected by the priority detection circuit 38, so this detection output is used to control the comparator 5o. The gain switching circuit 31 is designed to operate reliably so that the gain switching circuit 31 stably performs the gain switching operation for the automatic focus adjustment signal.

Further, the output of the synchronous detector 49 is transmitted to the LED drive circuit 23.
For example, if the subject is close,
When the amount of incident light increases due to a high reflectance of the subject and the DC output voltage of the synchronous detector 49 becomes high, the
The ED drive circuit 23 is controlled to reduce the amount of light emitted from the light emitting diode 240, and conversely, if the object is far away or the reflectance of the object is low, the amount of incident light decreases and the DC output voltage of the synchronous detector 49 decreases. When the value becomes low, the LED drive circuit 2 increases the amount of light emitted from the light emitting diode 24.
3 is controlled.

In place of the priority detection circuit 38, a priority detection circuit 54 configured as shown in FIG. 5 can be used. This priority detection circuit 54 has a contact terminal 55 of an electronic switch 55.
The input terminals of a, 55b and the comparator 56 are connected to the output terminals of the pre-stage amplifiers 26 and 27, respectively, and the comparator 5
The output terminal of 6 is connected to the drain side of FET (field effect transistor) 57. The gate of this FET57 is connected to the output terminal of OS C21 via a resistor 58,
A sampling hold capacitor 59 is connected between the source side of the FET 57 and ground. One end of this capacitor 59 connected to the source side of the FET 57 is connected to the control end of the electronic switch 55.
The movable contact piece B serves as the output end of this priority detection circuit 54.
Connected to PF48.

In the automatic focus adjustment device having this priority detection circuit 54, when out of focus, the amount of light incident on the light receiving elements 25a and 25b becomes unbalanced, and for example, the photocurrent Ia,
When Ib becomes the relationship Ia>xb, the preamplifier 26.
27(7) The output signals St and S2 also have a relationship of Sl>S2, and therefore, as shown in FIG. 6, the output s3 of the comparator 56 is in phase with the signal S1.82 and becomes "1" @ O
The signal changes to +1+. The output signal S3 of the comparator 56 is sampled by turning on the FET 57 at the output S4 of the OS C21. The output S4 of the OS C21 is the output signal S1. Since it is synchronized with the modulation waveform of S2, when the signal S3 is sampled by the FET 57, a 1" signal is held in the capacitor 59. Therefore, at this time, the movable contact piece of the electronic switch 55 is It is connected to the contact terminal 55a side, and the output signal s1 of the preamplifier 26 is guided to the BPF 48 as the output signal s5 of the priority detection circuit 54.

The photocurrent I a (I b becomes
When the output signal 5tySz of is in the relationship Sl < 82.

As shown in FIG. 6, the output signal of the comparator 56 is a signal Sa' which is the inverted phase of the signal S3.
9, the electronic switch 55 switches the connection to the contact terminal 55b side, and therefore the front stage amplifier 2
7 output signal S2 is detected with priority.

The output signal S5 of circuit 54 is directed to B P F 48 .

[Effects of the Invention] As described above, according to the present invention, there is a priority detection circuit that selectively detects the larger output of the two light receiving sections, so that the photocurrent with respect to the dark current is It is possible to detect the level of reflected light from the subject when the S/N ratio is large and the S/N is good. Therefore, if the output of this priority detection circuit is used to control the adjustment circuit that obtains the automatic focus adjustment signal. This has excellent effects such as greatly improving the focusing accuracy of automatic focus adjustment operations.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the basic circuit configuration of an automatic focus adjustment device of the present invention. FIG. 2 is a principle configuration diagram showing an example of an optical system in which an automatic focus adjustment device of the present invention is adopted; FIG. 3 is an electric circuit diagram of an automatic focus adjustment device according to an embodiment of the present invention; FIG. 5 is an electric circuit diagram showing another example of the priority detection circuit used in the present invention. FIG. FIG. 6 is a time chart showing waveforms of input and output signals of the priority detection circuit of FIG. 5. FIG. 1 ......--Light emitting element (light projection means) 3.1
0...Subject 4a14b, 25a, 25b@@, 2-split light receiving element (2 light receiving sections) 5...ell...Photographing lens 11...Light projection Means 12... Light receiving means 12&, 12b axis... Two light receiving sections 13... Adjustment circuit 14, 38, 54... Priority detection circuit 15...・・・・・・Gain adjustment circuit h1 Figure η2 factor 4 ward horse 5 ward, f54 Procedure amendment (voluntary) October 1985
May 11th 1, Incident Display 1985 Patent Application No. 8795
No. 0 No. 2, Title of the invention Automatic focus adjustment device 3, Name of the person making the correction (037) Olympus Optical Industry Co., Ltd. 4, Agent 5, "Detailed description of the invention" column of the specification subject to amendment and drawings 6. Contents of correction (1) Add "by light receiving lens 6" after "on r4a and 4b in the fourth line from the bottom of page 2 of the specification". (2) Delete the words after "photographing lens 5" in the second line of the same page and before "optical axis direction" in the third line, and substitute "ha". (3) “Tilt angle θ fluctuates” written in the 5th line of the same page,
Corrected to "The position in the left and right direction indicated by arrow X has changed." (4) At the end of the 6th line on the same page, replace "rotate." with "move."
Changed to (5) Add "incident light to" after "4b" in the 9th line of the same page. (6) The 11th item after “Inclination angle θ and,” in the 9th line of the same page.
Delete the part before "D" in the line and substitute "baseline length". (7) Among the drawings attached to the application, Figure 2 has been amended as shown in the attached sheet.

Claims (1)

[Scope of Claims] A light projecting means for projecting a light beam; a light receiving means having two light receiving sections for receiving a reflected beam of the light beam from a subject; an adjustment circuit that obtains an automatic focus adjustment signal based on the difference in light intensity; a priority detection circuit that receives the outputs of the two light receiving sections and selectively outputs the larger of the two outputs; An automatic focus adjustment device comprising: a gain adjustment circuit for adjusting the gain in the adjustment circuit according to the output.