JPH0521207B2 - - Google Patents

Description

[Detailed description of the invention]

Technical Field The present invention is directed to receiving an image of a subject through a photographing lens,
The present invention relates to an automatic focus adjustment device for a camera that automatically drives a photographing lens to a focus position based on a detection result of a focus detection device that detects the in-focus state. Prior Art A subject image from a photographic lens is received by a focus detection element array consisting of a large number of light receiving elements, and the output signal from this element array is processed to calculate the amount of defocus, that is, the amount of deviation of the image position from the film exposure surface ( For example, a device for detecting distance (distance)
No. 159,259 or US Pat. No. 4,185,191. However, when the focus detection device described above performs focus detection multiple times on the same subject at a fixed distance, the subject may change position in a plane perpendicular to the distance detection direction, or camera shake may occur when holding the camera. When the camera undergoes minute vibrations, the detection results do not necessarily match, and are distributed with slight variations around a certain value as the center value. In other words, there is a drawback that accurate focus detection information cannot be obtained with just one detection operation. This variation is caused by non-uniformity in the characteristics and arrangement of each element in the focused point detection element row, which consists of a large number of light receiving elements.
In addition to problems caused by instability of the processing circuit, when measuring the illuminance distribution on the detection element surface (corresponding to the subject luminance distribution), the focus detection element may be affected by the arrangement pitch of the detection element group arranged in a row. The spatial frequency characteristics of the subject are determined, and correct measurements cannot be made for frequency components higher than the spatial frequency determined by Nyquist's sampling theorem, or the brightness distribution of the subject may be affected by the dead zone that exists between the elements. This is due to the fact that the brightness is measured discontinuously, and even if there is a change in brightness in the dead band, it cannot be detected. Therefore, if the subject changes position in a plane perpendicular to the distance direction, the pattern of the subject image projected onto the focus detection element surface will change, and the relative sampling position of the subject image in the focus detection element array will also change. As a result, the detection results due to the above factors of the detection element may not match, and if the same measurement is repeated many times, the detection results will be distributed with some variation around a certain value. . Therefore, even if the focus of the photographing lens is adjusted based on the amount of defocus obtained in one detection operation, the accuracy of the adjustment is not guaranteed. Therefore, by detecting the in-focus state multiple times, we obtain data on multiple amounts of defocus and calculate their average value.
An apparatus that adjusts the focus of a photographic lens based on this average value has been proposed in Japanese Patent Laid-Open No. 78811/1983. However, in this proposal, the focus adjustment device is configured in such a way that the photographing lens is stopped and the detection operation is repeated, and the driving of the photographic lens is started after the average value is obtained, so the focus can be adjusted quickly. Nakatsuta. Therefore, the applicant of this application filed a patent application in 1983.
- In No. 157921, focus detection is repeatedly performed while moving the taking lens toward the in-focus position, and at that time, the amount of movement of the taking lens is detected using an encoder, and while the taking lens is moving, focus detection is repeatedly performed. The data for each differential focus amount collected is corrected by the amount of movement of the photographic lens, and each data is converted into data that can be considered to have been collected using a certain position as a reference position, and the average is calculated from the converted data. We proposed a focusing device that calculates the value. In this proposal, the average value is calculated by giving each data the same weight. By the way, it is said that the defocus signal detected by the above-mentioned focus detection device is more reliable as a signal when the photographic lens is slightly out of focus position than when it is far away from the in-focus position. I can point out the facts. Considering this fact, treating data collected at positions farther or closer to the in-focus position with the same weight will weaken the value of highly reliable data. . In addition, when using a system that measures the amount of defocus and moves the lens by an amount corresponding to that amount to perform focusing, the measured amount of defocus ε is multiplied by a certain conversion factor K to determine the focus. Calculate the rotation amount n of the motor required to reach the maximum temperature (n=
K·ε) A process is taken in which the motor is rotated by the determined rotation amount n to focus. In the case of regular fixed-focus lenses, once the lens is determined, the conversion factor K is also determined uniquely for that lens, but in the case of zoom lenses, even if the lens is determined, the conversion factor K is It is not determined uniquely, but changes depending on the zoom ratio, etc. While such a zoom lens is attached and an automatic focus adjustment operation is performed, shooting operations that change the zoom ratio may be performed at the same time.In this case, the conversion factor _K1 obtained before changing the zoom ratio is Motor rotation amount n ₁
If we average the motor rotation amount n ₂ obtained using the conversion factor K ₂ after changing the zoom ratio with equal weight, the result will be swayed by the past information of incorrect K ₁ , and the lens position will be changed. This results in unfavorable results for control. Purpose This invention was made in order to eliminate the above-mentioned drawback, and proposes a focus adjustment device with high focus adjustment accuracy. Summary The present invention repeatedly performs focus detection operations while moving the photographic lens toward the in-focus position, and corrects the amount of movement of the photographic lens for each detected defocus signal. Convert it to a signal that can be treated as the same as that taken from a certain position as a reference position, and calculate the average value of these signals,
In the camera's automatic focus adjustment device, which adjusts the focus of the photographic lens based on this average value, the defocus signal collected at a later timing in the chronological order is more accurate than the defocus signal collected at an earlier timing in the chronological order. In order to make effective use of the reliability of the defocus signal, we assign a large weight to the signal and perform statistical processing such as averaging, and put a larger weight on the signal collected when the photographing lens is closer to the in-focus position. It is characterized by what it did. Embodiment In FIG. 1, a single-lens reflex camera 2 in which a focus adjustment device according to the present invention is incorporated includes an optical system such as a photographic lens 4, a half mirror 6, and a pentaprism 8. Behind the half mirror 6, a submirror 10 is installed. The object light that has passed through the photographic lens, the half mirror, and the sub mirror is guided to the light receiving section 14 of the small point detection device 12. The photographing lens 4 has a built-in power transmission mechanism 20 configured with gears and the like that receives the driving force from the motor 16 and drives the lens group 18 back and forth along the optical axis.
The focus detection device 12 includes a CCD (charge coupled device) 14 as a light receiving section and a data processing circuit 2 that processes the output signal of the CCD and outputs a defocus signal.
Contains 2. The defocus signal includes information on the amount of shift from the in-focus position to the image position formed by the photographing lens and the direction of the shift. The configuration of the focus detection device 12 itself is well known as described above, and is not directly related to the present invention, so a detailed explanation thereof will be omitted. What is necessary for understanding the present invention is that the focus detection device 12 starts integrating the CCD when an integration start signal is applied from the outside,
When the integration is completed, an integration end signal is output to the outside, and then, after a predetermined data processing time has elapsed, a defocus signal is output, thereby repeating the detection cycle. The encoder 24 consists of a disk made of a repeating pattern of transparent and opaque parts fixed to the rotating shaft of the motor 16, for example, and a photocoupler arranged to sandwich the disk. (eg, P=12) pulses are generated. Once the configurations of the power transmission mechanism 20 and the encoder 24 are specified, the relationship between the number n of pulses from the encoder and the amount of movement l of the lens group 18 is determined. Note that power for operating the photocoupler is supplied to the photocoupler only when the motor is rotating. The central processing circuit 26 is detailed in FIG.
A drive control signal for the motor 16 is generated using the number of pulses and the like as input information, and outputted to the governor 36 as a motor drive circuit. The central processing circuit 26 is
It can also be closed to perform focusing operations.
The input information sources are the AF switch 28 and the RE switch 30, which is closed when the camera is in the shooting state. When the AF switch 28 is closed, focusing operation is started as described later, and the RE switch 3 is closed.
When 0 is closed, the focusing operation is interrupted. The governor 36 serving as a motor drive circuit receives a control signal from the central processing circuit 26 and controls power supply and braking to the motor 16. The motor 16 is rotated clockwise or counterclockwise in response to the control signal,
At this time, power is supplied continuously or intermittently. In the case of continuous power supply, the motor 16 rotates at high speed,
In the case of intermittent power supply, it rotates at low speed. Furthermore, if both ends are short-circuited, the motor will be in a state where sudden braking is applied. In the focus adjustment device according to the present invention, since a predetermined amount of time is required for integration into the CCD and processing of data, in order to perform the focusing operation in a short time, while moving the photographing lens toward the focusing position, The defocus signal detection operation is repeated. Therefore, the average value of the latest defocus signal and the previously detected defocus signals that are periodically output from the data processing circuit is taken, and the photographing lens is controlled using the average value. When averaging multiple defocus signals, the defocus signals output before the averaging process are corrected by an amount corresponding to the distance traveled by the photographing lens from the time of output to the time of the averaging process. and is converted into a defocus signal corresponding to the defocus amount at the position of the photographing lens at the time of averaging processing. For a plurality of defocus signals whose movement distances have been corrected in this manner, signals that are newer in time series are weighted more heavily, and an average value is determined.
This average value is set, for example, in a subtraction counter,
Thereafter, it is subtracted by pulses from the encoder.
In this way, the contents of this counter are corrected moment by moment to a value corresponding to the position of the photographing lens. The corrected contents of the subtraction counter are provided as final judgment data for motor control. 2nd below
The present invention will be explained in detail with reference to the drawings. In FIG. 2, the lens movement amount detection circuit 40 connected to the output of the encoder 24 detects the encoder 2 during the period from the start of the CCD integration to the end of the integration.
The number of pulses P ₁ output from the encoder 24 and the number P _{2 of output pulses from the encoder 24 during one detection cycle period from the start of integration until the output of the defocus signal are detected, and the number of pulses P 1 output from the encoder 24 is detected, and the number of pulses P 2} output from the encoder 24 is detected. The number of pulses P ₃ (=P ₂ -1/2P ₁ ) generated between the point in the middle of and the end of the detection cycle is determined, and the numbers P ₂ and P ₃ of pulses are output as output signals. In the detection circuit 40, the counter 42 is reset at the start of integration, and the encoder 2 is immediately
Count pulses from 4. The latch circuit 44 is
The count value _P1 of the counter 42 at the end of the integration is latched. The latch circuit 46 latches the count value _P2 of the counter 42 at the end of the detection cycle, that is, at the time when the defocus signal is output from the focus detection device 12 and taken into the latch circuit 52.
The multiplication circuit 48 multiplies the contents of the latch circuit 44 by 1/2 to obtain the number of pulses 1/ _2P1 . The subtraction circuit 50 is
The number of pulses is obtained by subtracting the number of pulses 1/2P ₁ from the number of pulses P ₂ .
Find P ₃ . Note that control signals necessary for the above calculation and control operations are provided from the system control circuit 58. The same applies to the following circuits. An output terminal 54 of the latch circuit 52 that takes in the defocus signal outputs a signal indicating the amount of defocus, and an output terminal 56 outputs a signal indicating the direction of defocus. The output terminal 54 is actually composed of, for example, a 16-bit signal terminal, and the output terminal 56 is composed of a 1-bit signal terminal. The multiplication circuit 60 multiplies the defocus signal given from the output terminal 54 by a constant coefficient α, and as a result, the defocus signal is transmitted to the encoder 2.
It is converted into a signal equivalent to the amount of lens movement indicated by the number of pulses of 4. Thus, from now on, the amount of defocus will be expressed on the basis of the number of pulses. The subtraction circuit 62 calculates the number of pulses from the number of pulses corresponding to the amount of defocus outputted from the multiplication circuit 60.
P ₃ is subtracted, and the lens movement amount corresponding to the number of pulses P ₃ is corrected. Such correction is performed for the following reasons. From a time perspective, the focus detection operation of the focus detection device 12 can be divided into a CCD integral photometry time and a subsequent signal processing time for obtaining a defocus signal. The integral light time varies depending on the brightness of the subject, but is, for example, 20 msec. Also, the signal processing time is approximately constant, for example 60
It is about m seconds. If the photographing lens is changing its position moment by moment during the integral side light, for convenience, the lens position at the time when half the integral time has elapsed will be regarded as the position of the integral side light. In this way, the focus detection device 12
The defocus signal output from the lens indicates the amount of defocus of this integral side light at the lens position, and the photographing lens has already moved by 70 msec in the above example from this position to the time when the defocus signal is output. Therefore, by subtracting the number of pulses P ₃ corresponding to this movement from the number of pulses corresponding to the defocus signal output from the multiplication circuit 60, the defocus signal at the photographing lens position at the time the defocus signal is output can be obtained. . Thus,
At the final point of the focus detection cycle, the subtraction circuit 62 obtains a defocus signal corresponding to the amount of defocus at the photographic lens position at that time. This corrected defocus signal is input to the next stage averaging processing circuit 64. However, the defocus signal from the second detection cycle onwards after the start of the focusing operation is taken into the averaging processing circuit 64. This is because the first detection cycle is normally performed with the photographic lens stopped, and only when it is determined that the lens is out of focus based on the obtained defocus signal, can the photographic lens be directed to the in-focus position. This is because the first movement is started, and the second detection cycle is started in parallel. Now, in the averaging processing circuit 64, the latch circuit 66 immediately takes in the distance-corrected defocus signal when it is output from the subtraction circuit 62.
The latch circuit 68 is a circuit that corrects the moving distance of the photographic lens as described above on the average value of the defocus signal, which will be described later, in a detection cycle earlier than the detection cycle in which the defocus signal taken into the latch circuit 66 was obtained. take in. The arithmetic circuit 70 is
The data of the latch circuits 66 and 68 are input and the calculation shown by the following equation is performed. _o = ay _o + (a-1) _o-1 ...(1) Here, y _o and _o-1 are the latch circuit 66,
This is the content of the signal latched at 68. Also, a
is a constant of 1<a<0, and is set to 0.5, for example. A latch circuit 72 latches the calculation result of the calculation circuit 70. The arithmetic circuit 74 passes the defocus signal of the first detection cycle applied via the multiplication circuit 60, and passes the signal from the latch circuit 72 in subsequent detection cycles. Latch circuit 76 latches the signal selected by selection circuit 74. Subtraction circuit 78 subtracts the contents of latch circuit 46 of lens movement amount detection circuit 40 from the contents of latch circuit 76 . In other words, the subtraction circuit 7
8 is to subtract the amount of movement of the photographing lens (corresponding to P2) over the detection cycle period during which the defocus signal _{y o} latched in the latch circuit ₆₆ was obtained from the previously averaged defocus signal y _o-1. As a result, the defocus signal is corrected to correspond to the amount of defocus at the photographing lens position at the time of the averaging process. The operation of the averaging processing circuit 64 will now be explained in order from the first detection cycle. The defocus signal y ₁ from the first detection cycle is inputted via the selection circuit 74 to the latch circuit 76 and a down counter 80 to be described later. When the defocus signal input to the counter 80 is determined to be out of focus by a determination circuit 82, which will be described later, driving of the photographing lens is started, and at the same time, a second detection cycle is started. It is assumed that the second defocus signal is then output after the required time. Then, the latch circuit 66 receives the number of pulses P ₃
The latch circuit 68 receives the second defocus signal _y2 whose distance has been corrected by the amount indicated by P2, and the first defocus signal _y11 whose distance has been corrected by the amount of movement indicated by the number of pulses _P2 . be included. Therefore, if the constant a in equation (1) is set to 1/2, the arithmetic circuit 70 outputs a signal ₂ expressed as ₂ = 1/2y ₂ + 1/2 ₁ (1)...(2) and the selection circuit 74
The signal is input to the latch circuit 76 and the down counter 80 via the latch circuit 76 and the down counter 80. However, ₁ (1) is the latch circuit 76
This means that the differential focus signal ₁ , which was latched in , has passed through the subtraction circuit 78 once and distance correction has been performed. The same applies hereafter. Similarly, when the third defocus signal _y3 is output from the subtraction circuit 62, an average value ₃ expressed by the following equation is obtained. ₃ = 1/2y ₃ + 1/2 ₂ (1) = 1
/2y ₃ +1/2 ² y ₂ (1)+1/2 ² y ₁ (2)...(3) When the fourth defocus signal y ₄ is obtained, ₄ = 1/2y ₄ +1/2 ₃ (1 ) = 1/2 ³ y ₂ (2) 1/2 ³ y ₁ (3) ... (4) An average value ₄ is calculated. Generally, when the nth defocus signal y _o is obtained, _o = 1/2 _{y o} + 1/2 ² y _o-1 (1) + 1/2 ³ y _o-2 (2) +...+1/2 ^n-1 An average value _o expressed as y ₂ (n-1)+1/2 ^n-1 y ₁ (n) (5) is calculated. As can be seen from equation (5), the latest data y _o is given the greatest weight, and the weight becomes lighter as you go back in time. As described above, in the averaging processing circuit 64,
The nth differential focus signal _{y o} which is the latest data
Once obtained, a defocus signal _o is calculated by averaging the n-1 pieces of past data. However, y _o indicates the output of the subtraction circuit 62 except for the first one. Note that the focus detection device 12
The data processing time from when the defocus signal is output to when the averaged signal is output is so short that it can be kept within the pulse interval output by the encoder 24. . Immediately after outputting the defocus signal, the focus detection device 12 is instructed to use the next integral side light and shifts to the next detection cycle. Now, when the defocus signal _o from the averaging processing circuit 64 is applied, the judgment circuit 82 generates the following signal according to the signal level. first,
The differential focus signal _o is set in the down counter 80, and thereafter the next differential focus signal _o+1
is subtracted by pulses from the encoder 24 until it is set. By doing this, the contents of the down counter 80 are corrected moment by moment to the defocus value _o ' at the current position of the photographing lens. This defocus signal _o ' is sequentially applied to two comparison circuits 84 and 86. Comparison circuit 84
compares the defocus signal _o ′ with a preset reference value d ₁ , that is, a value corresponding to the half-width of the near focus zone, which is set wider than the in-focus zone, and determines whether the defocus signal _o ′ is in near focus. If the zone value d is larger than d ₁ , a voltage signal of "high" level ("1") is output, and if it is smaller, a voltage signal of "low level" level ("0") is output. On the other hand, the comparison circuit 86 compares the defocus signal _o ' with a reference value _d2 corresponding to the half-width of the in-focus zone set in advance, and if the signal _o ' is larger than the in-focus zone value _d2 , it is set to a "high" level. outputs a voltage signal of , or a “low” level voltage signal if it is small. The output of the comparison circuit 86 is the AND gate 8
8 and 94 are connected to inputs 90 and 96, respectively.
The other input 98 of AND gate 94 is connected directly to the output 56 of latch circuit 52, and the other input 92 of AND gate 88 is connected to output 56 of latch circuit 52 through NOT circuit 100. It is assumed that the output 56 of the latch circuit 52 outputs, for example, a "high" voltage signal when the photographic lens is in front of the in-focus position, and a "low" voltage signal when it is behind. In this way, voltage signals as shown in Table 1 are output from each output terminal 101, 102, 103, 104 of the comparison circuits 84, 86 and AND gates 88, 94 according to the defocus signal _o ' and the direction signal. . In response to this output, the governor 36 drives and controls the motor 16 as shown in the rightmost column of Table 1. However, it is assumed that the photographing lens whose motor rotates clockwise is driven in the retracting direction.

【table】

Claims (1)

[Claims] 1. A focus detection device that receives the subject light that has passed through the photographic lens and repeatedly outputs two types of signals indicating the difference between the intended focal position and the imaging position and the direction of the imaging position with respect to the intended focal position, and the photographing lens. a correction means for correcting a plurality of signals indicating the difference repeatedly output from the focus detection device during the process of moving the lens toward a planned focal position into a difference signal corresponding to the current position of the photographing lens being driven; An averaging processing circuit that gives the largest weight to the newest signal among the plurality of corrected signals and calculates the average value of the plurality of signals, and a signal indicating the averaged difference from the averaging processing circuit. and a control device for controlling a photographing lens to a predetermined focus position based on a signal indicating a direction from the focus detection device.