JPS6256911A - Automatic focus detecting device - Google Patents

Abstract

PURPOSE:To decrease manufacturing processes, to reduce the cost and to improve focus detection precision by providing a switching means which outputs a sum signal and a difference signal on a time-division basis and narrowing down a focusing blind sector. CONSTITUTION:The sum signal (A+B) and difference signal (A-B) between the outputs of photodetection parts 5a and 5b are integrated by a single integration circuit 21 on a time-division basis to simplify the manufacturing processes relatively. Further, when the integration time T1 that the sum signal (A+B) requires to reach a specific value VX is shorter than a specific integration time TK, the integration time (limit integration time) T2 for the integration of the difference signal (A-B) is set double. Consequently, the width of the focusing blind sector becomes a half as large as usual and the focus detection precision is improved twice.

Description

Detailed Description of the Invention (Field of Application of the Invention) The present invention relates to an automatic focus detection device used in a video camera, etc., particularly an active type automatic focus detection device that projects light onto a subject and receives the reflected light to detect focus. This invention relates to improvements to automatic focus detection devices.

(Background of the Invention) FIGS. 6 to 8 show an example of a conventional automatic focus detection device of this type. In FIG. , reflected from three surfaces of the subject,
The light enters the light receiving element 5 via the light receiving lens 4. As can be seen from FIG. 7, the light-receiving surface of the light-receiving element 5 is divided into two light-receiving parts 5a and 5b.
The focus is detected based on each output signal, and as shown by the solid line in Figure 6, the object 3 is
The reflected light from the horn forms a spot light S at the center of the light receiving parts 5a and 5b.
(See Figure 7), the received light f + L ti at the light receiving sections 5a and 5b will be approximately equal as shown in Figure 7 (a), and if the subject is located far away like 3', , as shown in FIG. 7(b), the amount of light received by the light receiving section 5a is large;
The amount of light received by the light receiving section 5b decreases, and when the subject is located close like 3'', the amount of light received at the light receiving section 5b is large as shown in Fig. 7(c), and the amount of light received is The amount of light received by the light receiving part 5a decreases.In other words, as shown in FIG.
When the amount of light received by and 5b is almost equal, it is in focus, Fig. 7(b)
In cases like this, it is determined that the front side is in focus, and in cases such as that shown in FIG. (see Figure 6) to perform focus detection.

Next, the specific operation at the time of focus detection will be explained using FIG. The light receiving element 5 is configured to move via a cam or the like in conjunction with the movement of the photographing lens 6, that is, in conjunction with the rotation of the drive motor 7, and the light receiving elements 5a and 5b forming the light receiving element 5 At the latter stage, sensor amplifiers 8a and 8 are installed, respectively.
b, bypass filters 9a, 9b for removing DC components, synchronous detection circuits 10a, 10b, and integration circuits 11a, llb
is connected. The microcomputer 12 is the drive circuit 1
3 to the light emitting element 1 and the synchronous detection circuit 10a, 1
A pulse signal is output to 0b, and the light emitting element l emits pulse light according to this pulse signal, and the synchronous detection circuit 10a,
10b is a sensor amplifier 8 only during the period when the light emitting element l emits light.
Signals A and B input from a and 8b are input to integration circuits 11a and 11f.
Supply to lb.

Signals A and B photoelectrically converted by the light receiving sections 5a and 5b of the light receiving element 5 and outputted from the sensor amplifiers 8a and 8b are passed through bypass filters 9a and 9b and a synchronous detection circuit 10, respectively.
input to the integrating circuits 11a and llb via a and 10b,
The integrating circuit 11a.

After being integrated for a predetermined time by 11b, they are output to the next-stage addition circuit 14 and subtraction circuit 15, and rA+BJ
, rA-BJ is performed, and a predetermined threshold value VX, ±
A/D conversion circuit 16 consisting of a comparator with vy
．． Sent to 17. In the A/D conversion circuit J16, the integral value of the sum signal (A + B) and the threshold value Vz: are the same, and in the A/D conversion circuit 17, the integral value of the difference signal (A-B) and the threshold value ±vy are respectively The comparison results are sent to the microcomputer 12. As a result, microcomputer 1
2 determines whether the camera is in focus or out of focus (front focus, rear focus), that is, when the sum signal (A+B) reaches the threshold Vx, the difference signal (A-B) has not yet exceeded the threshold ±vy. It is determined that the focus is reached when a signal indicating
) has already exceeded the darkness value ±vy, it is determined that the focus is out of focus, and the focus detection signal N is immediately output to the drive motor 7 to move the photographing lens 6 and light receiving element 5 to a predetermined position. move in the direction. Thereafter, when the reflected light from the object is approximately equally incident on the light receiving sections 5a and 5b, the movement of the photographing lens 6 is stopped, that is, the output of the focus detection signal N is stopped.

In the device as described above, two integration circuits 14. are used to integrate the sum signal (A+B) and the difference signal (A-B).
15, it was necessary to adjust and equalize variations in the drift characteristics of each of the integrating circuits 14 and 15.

(Object of the Invention) An object of the present invention is to provide an automatic focus detection device that can solve the above-mentioned problems, reduce manufacturing steps, reduce costs, and improve focus detection accuracy.

(Features of the Invention) In order to achieve the L2 objective, the present invention includes a switching means for outputting a sum signal and a difference signal in a time-division manner, and a switching means that integrates the sum signal until it reaches a predetermined level, and then integrates the two difference signals. In-focus is determined when the integration level of the difference signal does not exceed the focus dead zone threshold within the integration limit time of the difference signal determined corresponding to the integration time of the sum signal and the integration means for integrating the sum signal. and calculation means for changing the focus dead zone threshold according to the magnitude of the integration time, so that a single integration means integrates the sum signal and the difference signal, and also integrates the sum signal. If the time is short, the integration limit time of the difference signal is set to a longer time than usual, or the focus dead zone threshold is set to a small value.

It is characterized by narrowing the out-of-focus zone.

(Embodiments of the Invention) Hereinafter, the present invention will be described in detail based on illustrated embodiments.

FIG. 1 is a block diagram showing one embodiment of the present invention. The same parts as in FIG. 6 are denoted by the same symbols. 18 is the sum signal (A+B
), 19 is a synchronous detection circuit 10a, l
A subtraction circuit 20 generates a difference signal (A-B) from the signal input from Ob, and 20 receives the sum signal (A+B) or receives the difference signal (A-B) according to a signal from a microcomputer, which will be described later. Switching circuit for selecting whether to attach or not, 21
22 is an integration circuit that integrates the sum signal (A+B) and difference signal (A-B) in a time-division manner, and 22 is an A/D conversion circuit consisting of three converters/ In the figure), 23 indicates the light emitting element l of approximately 10KH2.
The microcomputer generates a driving signal with pulses and controls the synchronous detection circuits 10a and 10b using this pulse signal. The integration time of the second mode is set depending on the length of the integration time in the first mode and the switching control between the first mode to select and the second mode to select the subtraction circuit 19 side. By changing the width of the dead zone, resetting the integrating circuit 21 at the end of distance measurement, and focusing by the signal from the A/D converting circuit,
It determines whether the lens is out of focus and controls the driving of the photographing lens 6.

FIG. 2 is a circuit diagram showing the inside of the A/D conversion circuit 22. As shown in FIG. 22a, 22b, and 22c are comparators, and the inverting input terminal of the comparator 22a has a threshold value Vx, the inverting input terminal of the comparator 22b has a threshold value (Vx+Vy), and the non-inverting input terminal of the comparator 22C (7) has a threshold value (Vx- Vy
) are applied respectively. 22d is switched according to a signal from the microcomputer 23, and the integration circuit 21
This is a changeover switch that outputs the integral output from the comparator 22a to either the inverting input end of the comparator 22a, or the non-inverting input end of the comparator 22b and the inverting input end of the comparator 22c.

Next, the operation will be explained using FIGS. 3 to 5. In the first mode, the switching circuit 20 connects the A/D conversion circuit 2 to the output side of the adder circuit 18, that is, the side that receives and receives the sum signal (A+B).
Since the changeover switches 22d of No. 2 have been switched to the state shown in FIG. Integration is performed for a time T until the applied threshold value Vx is reached (see Figure 3.4). When the integrated output reaches the threshold value Vx, the comparator 22a in the A/D conversion circuit 22 outputs a high level signal. When the signal is input, the microcomputer 23 switches the switching circuit 20 to the output side of the subtraction circuit 19, that is, to the side that accepts or accepts the difference signal (A-B).
d to the opposite side from that in FIG. 2, respectively, to shift to the second mode.

Incidentally, in such an active type automatic focus detection device, the farther the subject distance is or the lower the subject reflectance is, the worse the S/N ratio of the light reception signals at the light receiving sections 5a and 5b becomes. That is, the longer the integration time T1 until the sum signal (A + 8) reaches the threshold value Vx, the worse the S/N ratio becomes.
A stable focus detection signal N cannot be obtained. Therefore, even if the S,/N ratio is in such a poor state, a blind j1''f is provided so that the photographing lens 6 does not move erroneously at the in-focus position. This is the threshold value ±vy level shown in Figure 4. However, this threshold value ±vy level was set taking into consideration the situation when the S/N ratio is poor, so it is difficult to photograph a subject with a good S/N lt. In contrast, the advantage of being able to narrow the dead zone is wasted.Therefore, the microcomputer 2
3, it is determined whether the integration time T1 in the first mode obtained from the signal from the comparator 22a is shorter than the predetermined integration time Tk, and the next difference signal (A − B ,
) Set the integration time flit T 2 0 For example, if the integration time T1 in the first mode is longer than the predetermined integration time Tk, the integration time (integration limit time) in the second mode is set as shown in Figure 3. Set T2 to a time equal to the integration time T1 (CTi = T+ )L; conversely, if it is shorter, set the integration time T,
Is it more insensitive than when it is long? As shown in FIG. 4, the integration time is set to twice the integration time T1 (T2 =
2T, ) (see Figure 5).

In the second mode, the predetermined T2 time difference signal (A-B) set by the microcomputer 23 as described above is integrated. As a result, the light receiving section 5
If the outputs of a and 5b are equal, as shown by the solid line a in Figure 3.4, there is a slight difference between the outputs of the light receiving sections 5a and 5b, but there is a range that can be considered as in-focus, that is, a non-focus range that can be considered as in-focus. If the level difference is within the threshold value ±vy set corresponding to the focusing amount, the result will be as shown by the solid line in FIGS. 3 and 4. In both cases, the microcomputer 23 determines that the lens is in focus, the focus detection signal N is not output, and the photographic lens 6 is not driven.

On the other hand, when out of focus, the difference signal (A-8) is generated before 12 hours have elapsed.
The integral value of is the threshold (vx + Vy) or the threshold (Vx - Vy)
(see the third and fourth solid lines c), the output of the comparator 22b51c22c in the A/D conversion circuit 22 is inverted from a low level to a pi level signal, and this signal is input to the microcomputer 23. Therefore, the microcomputer 23 determines that the focus is out of focus, outputs a focus detection signal N to the drive motor 7, and moves the photographing lens 6 and light receiving element 5 in a predetermined direction. Incidentally, the moving direction at this time is determined by the output of the light receiving section 5a and 5, as is well known.
It is determined by comparing the magnitude of the output of b. After that, the same operation is repeated continuously, and the difference of 100 outputs from the A/D conversion circuit 22 between the light receiving sections 5a and 5b is the threshold value ±
When a signal indicating that the distance is within vy is output from the A/D conversion circuit 22, it is determined by the microcomputer 23 that the focusing sphere has been reached, and the photographing lens 6
The movement of the focus detection signal N is stopped, that is, the output of the focus detection signal N is stopped.

According to this embodiment, since the configuration is such that the sum signal (A+B) and difference signal (A-B) of the respective outputs of the light receiving sections 5a and 5b are integrated in a time-division manner by a single integrating circuit 21, The conventional work of adjusting drift characteristics can be eliminated, and the manufacturing process can be made relatively easy. Also,
If the integration time T1 until the sum signal (A+B) reaches the predetermined threshold value Vx is shorter than the predetermined integration time Tk, the integration time (integration limit time) T2 for integrating the difference signal (A-B)
Since it is set to twice the time, the width of the focusing dead zone becomes 1/2 of the normal width, and the focus detection accuracy can be doubled.

(Correspondence between the invention and the embodiments) In this embodiment, the light projecting element 1 is the light projecting means of the present invention,
The light receiving element 5 serves as a light receiving means, the adding circuit 18 and the subtracting circuit 1
9 is an addition means and a subtraction means, a switching circuit 20 is a switching means, an integrating circuit 21 is a dividing means 2, an A/Di switching circuit 22,
The microcomputer 23 corresponds to a calculation means, the darkness value Vx corresponds to a predetermined level, and the darkness value ±vy corresponds to a focusing dead zone threshold.

(Modification) In this embodiment, the sum signal (A + B) is set to a predetermined threshold value Vx
If the integration time T until reaching the predetermined integration time Tk is shorter than the predetermined integration time Tk, the integration time T for integrating the difference signal (A-B)
2 is set to twice the time, but the difference signal (A-
It is also possible to change the 1λ1 value ±vy to 1/2 without changing the integration time in B). Furthermore, the integration time T2 of the difference signal (A-B) may be set to an arbitrary time depending on the magnitude of the integration time T1 of the sum signal (A+B).

(Effects of the Invention) As described above, according to the present invention, there is provided a switching means for outputting a sum signal and a difference signal in a time-division manner, and a switching means for outputting a sum signal and a difference signal in a time-division manner, and a switching means that integrates a sum signal until it reaches a predetermined level, and then integrates a sum signal and a difference signal. an integrating means for integrating the signal, and determining that the focus is on when the integration level of the difference signal does not exceed the focus dead zone threshold within the integration limit time of the difference signal determined by [7] corresponding to the integration time of the sum signal; and oil quality means for changing the focusing dead zone threshold according to the magnitude of the integration time of the sum signal, and thereby the sum signal and the difference signal are integrated by a single integrating means, and the above-mentioned When the integration time of the sum signal is short, the integration limit time of the difference signal is set to a longer time than usual, or the focus dead zone threshold is set to a small value to narrow the focus dead zone. The number of manufacturing steps can be reduced, costs can be reduced, and focus detection accuracy can be improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing the configuration within the same <A/Z conversion circuit, and FIG. 3 is a diagram explaining the integration state of two types of signals. , FIG. 4 is a diagram explaining the integration state of two types of signals, FIG. 5 is a flowchart, and FIG. 6 shows a part of the distance measuring optical system arranged in a general automatic focus detection device. 7 are diagrams for explaining the incident state of spot light, and FIG. 8 is a block diagram of a conventional automatic focus detection device. 1... Light emitting element, 5a, 5b... Light receiving element, 18... Addition circuit, 19... Subtraction circuit, 20... Switching circuit, 21...
Integrating circuit, 22...A/D conversion circuit, 23...
...Microcomputer, A. B...Signal. Patent applicant Minoru Nakamura, representative of Canon Co., Ltd. Figure 6

Claims (1)

[Claims] 1. A light projecting means that emits light toward the object to be measured, and a means that receives the reflected light from the object to be measured and simultaneously and separately sends two types of signals that change relatively depending on the distance of the object to be measured. two light receiving means for outputting to the light receiving means, an adding means and a subtracting means for simultaneously and separately generating a sum signal and a difference signal of two types of signals inputted from the light receiving means, and a time-sharing method for generating the sum signal and the difference signal. a switching means for outputting; an integrating means for integrating the sum signal until it reaches a predetermined level; and then integrating the difference signal; , arithmetic means for determining focus when the integral level of the difference signal does not exceed a focus dead zone threshold, and changing the focus dead zone threshold depending on the magnitude of the integration time of the sum signal. Automatic focus detection device.