JPS61137119A - Automatic focus detecting device - Google Patents

Abstract

PURPOSE:To control a driving system for automatic focus detection by detecting synchronously outputs of two photodetector areas with a signal which does not synchronize with a pulse-modulated signal, and detecting only external light components inputted to the two photodetector areas on the basis of the synchronous detection outputs. CONSTITUTION:Pulse-modulated projection spot light is projected by a projecting element 31 on an object and its reflected light is photodetected by the two areas 35A and 35B, whose outputs are detected synchronously by the 2nd synchronous detecting circuits 61a and 61b with a signal which does not synchronize with the pulse-modulated signal, i.e. asynchronously with the 1st synchronous detecting circuits 42a and 42b. Only external light components are extracted as their output signals and inputted to a comparator 64 to calculate their difference, which is inputted to a succeeding stage comparator 65 to judge whether the difference is larger than a constant level VC or not; when the difference is larger than VC, it is inputted to a control circuit 51 to control the driving of a motor 36 for driving an image formation optical system. Consequently, stable operation is performed even against an object with large contrast.

Description

Detailed Description of the Invention <Industrial Application Field> The present invention is an active method having a drive motor that automatically detects the focus of an imaging optical system and moves the imaging optical system to a focused state. This invention relates to an improvement of an automatic focus detection device.

<Prior Art> Conventionally, as an automatic focus detection device for an imaging optical system, as shown in FIG. Project a projected light spot image, and transmit the reflected light to an infrared transmission filter 3.
, photosensitive areas 5A, 5 divided into two through the light receiving lens 4.
The light is received by the light receiving element 5 having the B, and the output signal is used to detect the distance to the object OB by the automatic focus detection circuit (hereinafter referred to as rAF circuit J), or to use the imaging optical system. Some systems detect the focus adjustment state, control the driving of the imaging optical system drive motor 6, and set the imaging optical system at the in-focus position.

In the figure, the light receiving element 5 moves in conjunction with the imaging optical system. That is, as can be easily understood from FIG. Assume that it is formed exactly between 5A and 5B. This state is shown in Figure 4 (a
), the photosensitive area 5A for the viewfinder field of view F.
, 5B are arranged one above the other, and a projected spot image P is formed in the middle part thereof.

Therefore, considering a state where the object OB is at a position S2 further away, the projected light spot image P reflected from the object OB is at a position closer to the photosensitive area 5A of the light receiving element 5, that is, as shown in FIG. ) is formed at the position Pa shown in ). Also,
Assuming that the object OB is at a nearby position S3, the projected light spot image P reflected from the object OB is at a position closer to the photosensitive area 5B of the light receiving element 5, that is, pb shown in FIG. 4(b). It is formed at the position of Therefore, when the object OB is at position S1, if the focal position of the imaging optical system is on the planned focal plane M (in-focus state), then the object OB is at position S1.
Even if an out-of-focus state occurs due to the two-way lens S3, by comparing the light receiving outputs of the photosensitive regions 5A and 5B of the light receiving element 5, the focal position of the imaging optical system can be determined on which side from the expected focal plane M. You can tell if it is out of alignment. Applying this principle, when the imaging optical system is out of focus, the light receiving element 5
The imaging optical system is moved along the optical axis in the direction of the in-focus position, depending on the magnitude of the output of the photosensitive areas 5A, 5B, manually or by a motor 6 or the like. Then, as the imaging optical system moves, the light receiving direction of the light receiving element 5 is changed, and when the projected light spot image P is formed exactly in the middle between the photosensitive areas 5A and 5B of the light receiving element 5, the light receiving direction is changed. If the focal position of the imaging optical system is placed on the planned focal plane M, the photosensitive area 5A
Focus detection of the imaging optical system can be performed by detecting that the difference in the received light outputs between the light and the light receiving outputs 5B and 5B has become zero. As a result, if the difference between the outputs of the photosensitive areas 5A and 5B of the light receiving element 5 is zero, it is in focus, and the output of the photosensitive area 5B is equal to the output of the photosensitive area 5A.
If the output is larger than the output of
If the output is larger than that of the photosensitive area 5B, the lens is rear focused (the focus position of the imaging optical system is on the rear side of the expected focal plane M). Therefore, if the imaging optical system is moved manually or by the motor 6, depending on the magnitude of the outputs of the photosensitive areas 5A and 5B, the front bin can be moved backwards, and the rear focus can be moved forward.
The imaging optical system can be brought into focus.

Therefore, FIG. 5 shows the configuration of the conventional AF circuit 7, and FIG. 6 shows an operating signal waveform diagram of the circuit.The focus detection function is performed on the photosensitive area of the light receiving element 5 as described above. Optical information received by 5A and 5B and photoelectrically converted is sufficiently amplified by amplifiers 11a and 11b. And the amplifier 11a.

11b has a frequency characteristic that has sufficient amplification for the modulation frequency of the projected infrared light that becomes the projected light spot image, and minimizes the amplification for the frequency of modulated light from unnecessary sunlight or commercial power. It is desirable to have an amplifier circuit with The output of this amplifier is applied to synchronous detection circuits 12a and 12b for synchronous detection. At this time, the synchronization signal has the same frequency as the light emission drive signal of the light projecting element 1, and maintains a constant phase relationship. The outputs of the synchronous detection circuits 12a and 12b are sent to an integrating circuit 13.
a and 13b, and increases moment by moment at an increasing rate proportional to the signal strength of the target signal. Integral voltage VA obtained independently from the integrating circuits 13a and 13b through the above signal processing.

VB is processed and determined by an arithmetic circuit, which will be explained below, and converted into several bits of digital information.

That is, the integrated voltages VA, VB are, on the one hand, subtractor 1
4 produces a difference signal VA Vl], and on the other hand, an adder 15 produces a sum signal VA + Ve. difference signal V
AVB is added to the absolute value circuit 16 and i VA-
Get Val. This value IVA-VBI is compared with a comparison value VD in a comparator 17, and the magnitude relationship thereof is output. On the other hand, the sum signal VA +Vn is compared with comparison values VL and V, respectively, in comparators 18 and 19, and the magnitude relationship between them is output. Also, the comparator 20 calculates the integrated voltage VA
, Vn are compared in magnitude.

The four digital information obtained from the above, ie, the outputs of comparators 17.18 and 19.20, are applied to the control circuit 21 to determine the operation of the entire system. Further, a synchronizing signal from a synchronizing signal forming circuit 22 connected to the control circuit 21 is applied to the synchronized detection circuits 12a and 12b, and is also applied to the light emitting drive circuit 23 to drive the light emitting element 1.
The motor drive circuit 24 controls the rotation direction and rotation speed of the imaging optical system drive motor 6 based on the signal from the control circuit 21. Control.

In the waveform diagram of FIG. 6, the synchronization signal 5YNC is also used to drive the current of the light emitting element 1 as described above, and the light emission output IR
ED can be obtained. On the other hand, the photosensitive areas 5A and 5 of the light receiving element 5
Output signal 5PC-A obtained from B.

5PC-B has a form in which the reflected light components a and b of the projected infrared light and the external light component C of sunlight or artificial light are superimposed.

Such signals 5PC-A and 5PC-B are supplied to the amplifier 11a.
.

The signal AMP- is amplified by the synchronous signal 5YNC and synchronously detected by the synchronous detection circuits 12a and 12b using the synchronous signal 5YNC.
A.

AMI) -B is obtained. CLR at the same time as it starts emitting light
When the signal is released, the signals AMP-A and AMP-B are integrated by the integrating circuits 13a and 13b, and the output signal Int
-A.

Int-B is obtained.

In FIG. 6, the so-called external light component C such as sunlight or artificial light is a signal 5PC-A.

As shown in the waveform 5PC-B, it is assumed that the same amount of light is output to the photosensitive areas 5A and 5B.

In this way, the output signals NT-A, Int-B, that is, the integral outputs VA, Vn are obtained, and IVAVBI and VA+VB are obtained as described above, and focus detection is performed using these values and the outputs of the comparators 17 and 18419.20. , that is, the method for determining focus, front focus, and rear focus is the seventh method.
This will be explained with a diagram.

As shown in Fig. 7(a), a given product − with +Vn
If VB l <VD, it is determined that the state is "in focus". In other words, in-focus is achieved when both VA and VB have sufficiently large outputs and the difference between them is VA-Vn.

Next, Figure 7 (b) Nioite, l VA Vn l
A certain predetermined integration time T. Find Vh + VB at time t when it reaches level VD within
If +Vn<VH, it is assumed that there is a relatively small out-of-focus state, and at the same time, VA and VB are determined by the comparator 20, and if VA>Ve or VA<VB, the drive motor 6 is brought closer at a low speed. Further, Fig. 7 (C) Nioite, IVA Vol.
If VA + VB < VL at the time of -Vn, it is assumed that the focus is significantly out of focus and the drive motor 6
drive at higher speed.

<Problems to be Solved by the Invention> By the way, as in the above-mentioned conventional device, the photosensitive areas 5A, 5
In a system that determines the focus state based on the magnitude of the output of B, if the subject itself has different reflectances (emission wavelengths of the light projecting element) in areas F, , F2, as shown in Figure 4 (C). If the contrast is different, it happens that the boundary of area F, , F2 and the sensitive area 5 A, ,
5B, even if the spot image P evenly straddles both the photosensitive areas 5A and 5B and is in focus, the area F,
, due to the difference in reflectance of F2, the photosensitive areas 5A and 5B
This results in a difference in the output of the camera, which may result in what is called a malfunction, which is considered to be out of focus.

The present invention eliminates the drawbacks of the conventional example described above, and provides an active automatic method that is free from the influence of external light components and does not cause malfunctions in focus judgment even if the subject has a difference in reflectance in that area. An object of the present invention is to provide a focus detection device.

〈Failure to solve the problem〉 The present invention will be explained using FIG. 1 corresponding to an embodiment.

A pulse-modulated spot light from the light projecting element 31 is projected onto the subject, and the reflected light from the subject is received by the two areas 35A and 35B of the light receiving element 350, and the outputs of the two light receiving element areas are converted into the pulse modulated signal. In the automatic focus detection device, the first synchronous detection circuits 42a and 42b perform synchronous detection using a signal synchronized with the first synchronous detection circuit, and the control circuit 51 detects the in-focus state or out-of-focus state based on the first detection output. The outputs of the two light-receiving element regions 35A and 35B are synchronously detected by second synchronous detection circuits 61a and 61b using signals that are not synchronized with the pulse modulation signal, and the two light-receiving elements are detected based on the second detection outputs. The external light component of the output of the area is detected as an output signal, and the output signal is sent to the comparator 6.
The signal is inputted to the control circuit 51 via the 4°65 signal to control the drive system for focus detection.

Effect> The light reflected by the subject of the pulse-modulated projected spot light projected from the light-emitting element 31 is received by the two regions 35A, 35B of the light-receiving element 35, and its output is not synchronized with the pulse-modulated signal. The signals, that is, the first synchronous detection circuits 42a and 42b are synchronously detected by the second synchronous detection circuits 61a and 61b, respectively, at asynchronous timing. Then, the output signal consists of the external light component and the reflected infrared light component, which are the outputs of the two light-receiving element regions.
Only the external light component is extracted, and the two output signals are input to the comparator 64 to find the difference, and the difference signal is input to the next stage comparator 65 and is constant and larger than the bell c. If it is larger than Vo, it is input to the control circuit 51 to control the driving of the imaging optical system driving motor 36.

<Embodiment> FIG. 1 is a block circuit diagram of an embodiment of an automatic focus detection device according to the present invention, and FIG. 2 is a diagram of its operating signal waveform.

In FIG. 1, two areas 35A and 35B of the light receiving element 35 receive the reflected light of the near-infrared spot light from the light projecting element 31 projected onto the subject, and photoelectrically convert the light. There is. Respective areas 35A, 35
The output of B is amplified by amplifiers 41a and 41b, and the output of each amplifier 41a and 41b is amplified by the light projecting element 31.
A signal 5YN synchronized with the pulse-modulated light emission drive signal of
At C, synchronous detection is performed by first synchronous detection circuits 42a and 42b, and the outputs of the first synchronous detection circuits 42a and 42b are integrated by first integration circuits 43a and 43b to obtain outputs VA and Vn, respectively, On the other hand, this is applied to the subtracter 44 and the absolute value circuit 46.
On the other hand, the adder 45 calculates VA +VB. This value 1VA Vn l is compared with the comparison level VD in the comparator 47, and VA +VB
are comparison levels VL in comparators 48 and 49, respectively.

-11 ~ (1) H is compared, and the magnitude relationship between VA and VB is compared by a comparator 5C, and the outputs of these comparators 47, 48, 49, and 50 are input to the control circuit 51 and focused.

A determination is made as to whether the lens is out of focus, and a signal from the control circuit 51 based on the determination controls the rotational direction and rotational speed of the imaging optical system drive motor 36 via the motor drive circuit 54. Further, a synchronizing signal 5YNC from a synchronizing signal forming circuit 52 connected to the control circuit 51 is inputted to the synchronous detection circuits 42a and 42b and also inputted to the light emitting element light emission driving circuit 53 to cause the light emitting element 31 to emit light. Controlled by pulse modulation. The above configuration is similar to the conventional example described above.

Further, second synchronous detection circuits 61a and 61b are connected to the output sides of the amplifiers 41a and 41b, respectively,
The second synchronous detection circuits 61a and 61b receive the signal PI-8YNC from the phase inversion (or shift) circuit 63 connected to the synchronous signal forming circuit 52, and synchronize the first synchronous detection circuits 41a and 41b. What is timing?18
The timing is shifted by 0°, that is, the light emitting element 31 in FIG.
The pulse-modulated light emission output ■RED is synchronously detected at an asynchronous timing. Furthermore, the output sides of the second synchronous detection circuits 61a and 61b are connected to second integration circuits 62a and 62b, respectively, and the output sides of the second integration circuits 62a and 62b are connected to a comparator 64.
The output side of the comparator 64 is connected to the constant voltage V of the next stage.
The output of the comparator 65 is input to the control circuit 51.

Therefore, in the waveform diagram of FIG. 2, the output signal 5PC-A from the two regions 35A and 35B of the light receiving element 35.

The waveform of 5PC-B is the same as that of the conventional example shown in Fig. 6, but the level of the output signal 5PC-A is the superposition of the external light component c1 and the reflected infrared light component a, and the output The level of the signal 5PC-B is the superposition of the external light component c2 and the reflected infrared light component, and unlike in FIG. 6, cl:'I:c
This is a case where the external light components are different in the regions 35A and 35B.

These output signals 5PC-A and 5PC-B are amplified by amplifiers 41a and 41b, respectively, and are detected by the first synchronous detection circuits 42a and 42 using the waveform of the synchronous signal 5YNC.
1) synchronously detects the signals AMP-A, AMP-B.
are obtained, and their amplitudes are c, +a, and c2-1, respectively.
-b.

Here, the output signals 5PC-A and 5PC-B are a signal whose phase is inverted from that of the synchronizing signal 5YNC, that is, P■-8.
The second synchronous detection circuit 61a, 611 uses the YNC waveform.
), the output signals A, MP-A,
.

The waveforms A and MP-B' have amplitude levels in which only the external light component CI + c is extracted.

These output signals AMP-A';AMP-B' are inputted to the second integration circuits 62a and 62b, and further to the comparator 6.
4, the difference is determined by the comparator 65 in the next stage, and the difference is determined to be constant. Decide whether it is larger or smaller.

As a result of that judgment, v. If larger, area 35A
It is determined that there is a large difference between the external light components incident on the area 35B and the area 35B, that is, the object has a large contrast difference, and its output is input to the control circuit 51, and the imaging optical system driving motor 36 is stopped. , or control a drive circuit for automatic focus detection, such as lighting a warning lamp.

<Effects of the Invention> As explained above, the present invention eliminates the influence of external light components incident on the light receiving element together with reflected infrared light, and operates stably even for subjects with large contrast differences. There is an effect that it can be used as an automatic focus detection device.

[Brief explanation of drawings]

FIG. 1 is a block circuit diagram of an embodiment of an automatic focus detection device according to the present invention, FIG. 2 is an operation signal waveform diagram thereof, FIG. 3 is a schematic configuration diagram of a conventional automatic focus detection device, and FIG. a)
(b) (C) is an explanatory diagram of the light receiving state of the light receiving element, the fifth
The figure is a block circuit diagram of the automatic focus detection circuit, FIG. 6 is an operation signal waveform diagram thereof, and FIGS. 7(a), (b), and (C) are operation characteristic diagrams of the focus determination method. 31. Light emitting element, 35... Light receiving element, 35A, 35
B... Light-receiving element area divided into two, 36... Imaging optical system drive motor, 41a, 41b-Amplifier, 42a
, 42b-first synchronous detection circuit, 43a, 43
b: first integration circuit, 44: subtracter, 45: adder, 46: absolute value circuit, 47.48, 49.50: comparator, 51 control circuit, 52: synchronization signal forming circuit, 53・
Light emitting element light emission drive circuit, 54...Motor drive circuit, 6
1a. 61b... second synchronous detection circuit, 62a, 62b...
...Second integration circuit, 63...Phase inversion circuit, 64.6
5... Comparator Figure 4 (a) (b) (c) ぃ/

Claims (1)

[Claims] 1 Project a pulse-modulated spot light from a light projecting element onto a subject, receive reflected light from the subject by two areas of a light receiving element, and synchronize the outputs of the two light receiving element areas with the pulse modulation signal. In an automatic focus detection device that performs first synchronous detection based on the detected signal and detects in-focus and out-of-focus states based on the first detection output, the outputs of the two light receiving element areas are used as the pulse modulation signal. Performing second synchronous detection using unsynchronized signals, and controlling the drive system for automatic focus detection by detecting only external light components input to the two light receiving element areas based on the second detection output. An automatic focus detection device featuring: