JPH02207229A - Automatic focus adjusting device - Google Patents

Abstract

PURPOSE:To adjust the focus accurately following up a subject in quick motion by deciding whether a correction is made with a found correction quantity or not by using not only the variation quantity of the moving speed of a subject image, but also its variation rate. CONSTITUTION:The automatic focus adjusting device consists of, for example, an in-camera control circuit PRS, a line sensor device SNS, a motor LMTR, an encoder circuit ENCF, a lens communication buffer circuit LCM, etc. Then the variation rate and variation quantity of the moving speed of the subject image plane position are used by a decision means to decide whether the correction value found by a correcting means is added to the quantity of defocusing detected by a focus detecting means or not. When this decision is made, the variation rate of the moving speed of the subject image plane is used first and when it is judged that the correction value is improper, the variation quantity of the speed of the subject image is used for the decision making. Consequently, the focus can be adjusted accurately following up even the subject in quick motion.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Application of the Invention) The present invention relates to an improvement in an automatic focus adjustment device used in a camera.

(Background of the Invention) Conventionally, many automatic focusing systems for reflex cameras attempt to focus on a subject by repeating the cycle of "focus detection (sensor signal input, focus detection calculation), and lens drive." It is something to do. The amount of lens drive in each cycle is based on the amount of defocus at the time point when focus detection is performed in that cycle, and this is expected to eliminate the amount of defocus at the time of focus detection when lens drive is completed.

Naturally, focus detection and lens drive require a considerable amount of time, but in the case of a stationary subject, the amount of defocus will not change unless the lens is driven, so lens drive is The amount of defocus to be canceled at the time of completion is equal to the amount of defocus at the time of focus detection, and correct focus adjustment is performed.

However, in the case of subjects with large movements, focus detection,
The amount of defocus changes during lens driving, and the defocus amount to be eliminated and the detected defocus amount may be significantly different, resulting in a problem that the subject is out of focus when the lens driving ends.

As an automatic focus adjustment device aimed at solving the above problems,
JP-A-62-125311, JP-A-62-13951
Publication No. 2, Publication No. 62-139511, Publication No. 62-26
No. 9936 and the like are disclosed.

The gist of the automatic focus adjustment method in the device disclosed in the publication is that the lens is driven by predicting the defocus change caused by the movement of the subject, taking into account the detected defocus change in each cycle and the time interval of each cycle. This method is expected to correct the above problem from the viewpoint of focusing accuracy at the end of driving the lens.

On the other hand, when performing the above correction, there is no problem if the focus detection result is for the original subject, or if a different subject is mistakenly measured or the subject is removed from the focusing point. For example, if a correction is applied using the correction amount obtained from the detection result obtained as is, the lens will be driven in a direction completely different from that of the original subject.

As an automatic focus adjustment device aimed at solving the above problems,
The applicant of the present application has proposed Japanese Patent Application No. 62-328233.

The gist of the proposed device is to calculate the amount of correction obtained by focusing on the amount of change in the moving speed of the object image plane position, the coefficient of the approximation function, the amount of lens drive, the amount of detected defocus, etc. obtained in the process of calculating the amount of correction described above. The decision is made as to whether or not an amendment should be made, and from the standpoint of not making incorrect amendments,
This device is expected to improve the above problems.

However, when performing automatic focus adjustment using the method described above, for example, in determining whether or not to perform correction based on the obtained correction value, only the amount of change in the moving speed of the subject image plane position is considered. , the following problems may occur.

In other words, even if you are tracking the subject correctly, if the subject approaches the photographer, the speed of change in the subject image plane position itself will be large, and the amount of change will also be large. Correction will be stopped due to the judgment, resulting in an out-of-focus shot. In other words, by making the determination, the original performance of the correction method described above is degraded.

FIG. 8 is a diagram for explaining the conventional lens drive amount correction method, in which the horizontal axis represents time t and the vertical axis represents the image plane position d of the subject.

The trajectory f (t) indicated by a solid line means the image plane position of the subject, and the trajectory f2 (t) indicated by a broken line means the image plane position of the lens.

To explain in more detail, f (t) is when the focusing optical system of the photographic lens is at the position where the focal point is focused at infinity.
Time t of the subject approaching the camera in the optical axis direction
ρ(1) means the image plane position of the same subject at the focusing optical system position at time t. The interval [ti, ti' is the focus detection operation, [ti
'ti+1] corresponds to the lens driving operation.

Therefore, f (t) and β (1) at the same time t
The difference in the vertical axis d direction is the so-called defocus amount.

DFi is the detected defocus amount at time ti,
DLi represents the lens drive amount of the image plane position replacement calculation executed from the focus detection result at time ti-1, and TMi represents the time interval of the focus adjustment operation.

In the conventional example shown in the figure, the assumption for performing the correction calculation is that the image plane position of the object changes according to a quadratic function. That is, at time t3, the current and past three image plane positions (tt, fl), (t2.f2
), (t3°f3), it is assumed that the image plane position f4 at time t4 can be predicted.

However, what the camera can actually detect is the image plane position f
,,f2. Defocus amount DPI, DF instead of f3
2. DF3 and image plane movement amount converted lens drive amount DLI,
It is DL2. The time t4 is just a value in the future, and in reality, it is a value that changes as the storage time of the storage sensor changes depending on the brightness of the subject.
When determining f4, for simplicity, t4-t3 = t3
It is assumed that the relationship t2 is known.

Under the above assumption, when the lens is driven from the focus detection result at time t3 to time t4 at time t3', the lens drive in terms of the amount of image plane movement is determined as follows.

a −t2+b −t+c=f (t) (1
)a-t12+b-tl +c=f(ti)(2)a-
t2''+b-t2+C=f (t,)(2')a-t3
2+b-t3 +c=f (t3) (2") In Figure 8,
Considering the 41st point as the origin, fl=DF1 (3) fz
=DF2+DL1 (3')f3=
DF3+DL2+DLL (3″)t+=o
(4) t2=TM1
(4') t3 = TM1 +
TM2 (4″) Above formula (3), (
3'), (3''), (4), (4').

Substitute (4") into (2), (2'), (2") and complete a.

When calculating bc, c = DF1...
(7) Therefore, the lens drive amount DL3 converted to the amount of image plane movement at time t4 is DL3=f4-123"fa (fz DF3) = a (TMI+TM2+TM3) 2+b (TM
1+TM2+TM3)+c-(a(TM1+TM2)2
-b(TM1+TM2)+c) +DF3= a (
(TM1+TM2+TM3) 2- (TM1+TM2
) ” )+ bTM3+DF3
(8) Here, assuming that TM3 is known from the relationship TM3=TM2 as described above, DL3 is found from equation (8).

Similarly, the lens drive amount at ti after time t4 is determined by the past three detected defocus amounts DF i-2, DF
i-1, DF i, the past two actual lens drive amounts DLi-2, DLL-1, and the past two time intervals T
It can be determined from M i -2 and TM i -1.

DLi=ai ((TMi-2+ TMi-1+ TM
i)”(TMi-2+ TMi-1)2) +bi-
TMi+DFi (11) Above formula (9), (1
0), according to (11), the detected defocus amount DFi
If the lens is driven by determining the defocus amount DLi for driving the lens, it is possible to always properly focus even a moving subject at the end of driving the lens.

In addition, in the above correction method, since the image plane position is extrapolated using a quadratic function, data of at least two past focus adjustment operations are required. However, since there is insufficient data for the first two times after starting the focus adjustment, as shown in Figure 8, the lens is driven based on the detected defocus amount itself for the first two times of the focus adjustment operation, as shown in Figure 8. do. That is, the actual correction calculation is performed from the third lens drive, and as shown in FIG. 8, the correction effect appears from time t4.

Next, the object image plane movement speed will be explained.

In FIG. 8, two points f1. on f(t). The object image plane movement speed V12 between f2 is the slope of the straight line connecting these two points f1°fz. Similarly, two points f2.
The object image plane movement speed V23 during f3 is as follows.

Judgment based on the amount of change in these two values is Vd=V12-V23...
... Calculate Vd using the formula (14), and calculate this Vd
d or the absolute value 1Vdl is the judgment standard (taken as Vo)
The judgment is made by comparing the For example, lVd is V
If it does not exceed o, it is considered appropriate.

Here, if the determination reference value V○ is small, the determination will be immediately affected and the continuity of the correction effect will be lost, and if it is large, the determination will have almost no meaning.

FIG. 9 is a diagram when the above-mentioned correction is applied to a subject approaching the photographer using a determination method that focuses only on the amount of change in the subject's image plane movement speed. Similar to FIG. 8, the horizontal axis is At time t, the vertical axis represents the image plane position d of the subject, f (t) represents the image plane position of the subject, and locus ρ(1) represents the image plane position of the lens.

The correction works effectively until time t1, and the lens is driven very well. However, when the above determination is made using the detected defocus amount DPI at time t1, it is determined to be inappropriate. Next, time t1'
Although only focus detection was attempted again, it was determined to be inappropriate again, and in the end, lens drive DLL was performed using the final focus detection result DF1'. After performing lens drive DL2 based on the detected defocus amount DF2 at time t2,
Focus detection is performed at time t3, and this result is used to make corrections from the next lens drive, but as you can see from the figure, the amount of change in the image plane position is large, and at time t1. Since it was determined to be unsuitable at time t1', it is clear that it is also determined to be unsuitable at time t3 and at time t3' when the distance was measured again. In the end, the correction means is not effectively utilized at all after time t1, such as performing lens drive DL3 based on the distance measurement result at time t3'.

In this way, even though the image plane position of the subject is changing smoothly, focus detection is performed at certain time intervals, so if you get stuck in - degree judgment, you may not be able to recover after all. Become.

(Objective of the Invention) The object of the present invention is to solve the above-mentioned problems, and to correct the problems described above.1] Perform focus adjustment that accurately follows even fast-moving subjects without sacrificing the original purpose of correcting the subject. An object of the present invention is to provide an automatic focusing device capable of adjusting the focus.

(Features of the Invention) In order to achieve the above object, the present invention uses the rate of change and amount of change in the moving speed of the object image plane position obtained in the process of determining the amount of correction to determine the amount of defocus from the focus detection means. A determination means is provided for determining whether or not to add the correction value obtained by the correction means to It is characterized in that it is performed not only based on the rate of change, but also based on the rate of change.

(Example of the invention) First, an overview of one embodiment of the present invention will be described.

When determining whether or not to perform correction based on the obtained correction amount, first, a determination is made based on the rate of change in the subject image plane movement speed, and if it is determined that it is inappropriate based on this determination, a further determination is made based on the amount of change in the subject image plane velocity. I do. By using this two-stage determination method, it becomes possible to perform an effective determination without impairing the original performance of the correction.

Therefore, in order to make the first determination, we need to determine the function representing the image plane position of the subject at three points (the 8th
fl, f2. f3) Two object image plane movement speeds between VI2. Find V23. From these two values, a value Vc representing the amount of change is determined as follows.

This equation (15) applies only when V12 and V23 are equal.
It becomes o2. Other than this, the values correspond to the amount of change in V12 and V23. Further, if the directions of VI2 and V23 are the same, it will be a positive value, and if the directions are reversed, it will be a negative value.

For example, if the voltage changes twice in the same direction, Vc=2.5.

Using the value Vc as described above, the change in direction of the image plane velocity is checked, and if the direction has not changed, the value of Vc is further compared with a predetermined determination value (denoted as Vp). If Vc does not exceed Vp, it is determined that the rate of change is appropriate, and the lens driving amount is corrected using the obtained correction amount.

On the other hand, if the direction changes or VC exceeds Vp, the following determination is made. The second stage determination is performed by comparing the absolute value 1vd1 of the amount of change in image plane velocity with a predetermined reference value V○, as described above. However, appropriate and effective determination can be made by using a reference value Vo in this case that is smaller than the conventional value.

The purpose of each of the above-mentioned two-step determinations is to first check whether the value of Vc is positive or negative, and then compare it with the value of Vp to determine whether the velocity change in the image plane position of the subject is smooth. It is something. Next, even if it is determined that the speed change is not smooth, especially if the image plane movement speed itself is relatively small, the image plane movement may not be smooth due to an error in the focus detection result, and the absolute value lVd1 When the value is small, the result is not a result of erroneous distance measurement, so it is determined that correction should be performed using the correction amount obtained as is.

FIG. 2 shows an example in which the lens is driven using the above determination for the same subject as in FIG. 9. As can be seen from this figure, excellent lens driving is performed even in a region where the rate of change of the subject image plane position itself is high without interrupting the correction midway as shown in FIG.

In other words, in the conventional method of driving the lens by adding a certain amount of correction to the amount of defocus detected in order to take a picture of a moving subject in focus, actual correction is performed using the amount of correction found. By making a two-step determination using the rate of change and the amount of change in the moving speed of the object image plane position, it is possible to always perform appropriate correction without degrading the performance of the correction method.

Flowcharts showing the structure and operation of the apparatus for realizing the above are shown in FIGS. 1, 3 to 6 below.

FIG. 1 is a circuit diagram showing a camera equipped with an apparatus according to an embodiment of the present invention.

In the figure, PH1 is a camera control circuit, for example, it includes a CPU (central processing unit), ROM, and RA.
It is a one-chip microcomputer with MA/D conversion function. Camera control circuit PR3 (hereinafter simply PH1
) performs a series of camera operations such as automatic exposure control function, automatic focus adjustment function, film winding and rewinding, etc., in accordance with the camera sequence program stored in the ROM.

Therefore, PH1 uses communication signals SO, SI, 5CL
K.

Communication selection signals CLCM, C5DR, and CDDR are used to communicate with peripheral circuits within the camera body and the control device within the lens, thereby controlling the operation of each circuit and lens.

The signal SO is a data signal output from PH1, SI
is the data signal input to PH1, 5CLK is the signal SO
, ST synchronous clock.

LCM is a lens communication buffer circuit, and when the camera is in operation, it supplies power to the lens power supply terminal VL, and the selection signal CLCM from PH1 is at a high potential level (hereinafter abbreviated as "H°'", low potential level). (abbreviated as L°'), it serves as a communication buffer between the camera and the lens.

When PH1 sets the signal to "H" and sends predetermined data as signal SO in synchronization with SCL, lens communication buffer circuit LCM sends each buffer of 5CLK and SO via the camera-lens communication contact. Signal LCK,
Output DCL to the lens. At the same time, the buffered signal of the signal DLC from the lens is output as the signal SI,
PH1 inputs the signal SI as lens data in synchronization with 5CLK.

SDR is a drive circuit for a line sensor device SNS for focus detection composed of a CCD, etc., and the signal C3DR is “
It is selected when the signal 5O1Sl, SC
, L to PI (controlled from S. Signal CJ is C
CD driving clock φ1. The signal INTEND is a clock for generating φ2, and the signal INTEND is a signal that notifies PH1 that the accumulation operation has ended.

The output signal O3 of the line sensor device SNS is the clock φ1
．． It is a time-series image signal synchronized with φ2, and the drive circuit SD
After being amplified by the amplifier circuit in R, P is output as image signal AO3.
Output to H1. PH1 inputs the image signal AO3 from an analog input terminal, and in synchronization with CK, uses an internal A/D conversion function to sequentially store it as a digital signal at a predetermined address in the RAM.

Signal 5AG which is also the output of the line sensor device SNS
C is AGC (automatic gain control: Au
This is the output of the to Ga1n ControlJ sensor, is input to the drive circuit SDR, and is used for storage control of the device SNS.

SPC is a photometric sensor for exposure control that receives light from the subject through the photographic lens, and its output of 5 spc is input manually to the analog input terminal of PH1, and after A/D conversion,
Used for automatic exposure control according to a predetermined program.

DDR is a switch detection and display circuit, and the signal C
It is selected when DDR is "H" and the signal s.

, Sl, controlled from PH1 using 5CLK. That is, based on the data sent from the PH1, the display on the display member DSP of the camera is switched, and the on/off states of various operating members of the camera are notified to the PH1 through communication.

SWI and SW2 are switches linked to a release button (not shown); when the release button is pressed in the first step, the switch SWI is turned on, and subsequently, when the release button is pressed in the second step, the switch SW2 is turned on. PH1 performs photometry and automatic focus adjustment when the switch SWI is turned on, and performs exposure control and film winding when the switch SW2 is turned on as a trigger.

The switch SW2 is connected to the "interrupt input terminal" of the microcomputer PH1, and the switch SW2 is connected to the "interrupt input terminal" of the microcomputer PH1.
An interrupt is generated by turning on W2, and control can be immediately transferred to a predetermined interrupt program.

MTRI is for film feeding, MTR2 is for mirror up/
It is a motor for down and shutter spring charging,
Forward rotation and reverse rotation are controlled by respective drive circuits MDRI and MDR2. Signals manually input from PH8 to MDRI, MDR2 MIF, MIR, M2F, M2
R is a signal for motor control.

MGI and MG2 are magnets for starting the running of the front and rear shutter curtains, respectively, and are energized by signals SMGI and 5MG2 and amplification transistors TRI and TR2, and shutter control is performed by PH1.

Note that the switch detection and display circuit DDR, motor drive circuits MDRI and MDR2, and shutter control are not directly related to the present invention, so detailed explanations will be omitted.

A signal DCL input to the intra-lens control circuit LPR3 in synchronization with LCK is data of a command from the camera to the lens FLNS, and the operation of the lens in response to the command is determined in advance. The in-lens control circuit LPR3 analyzes the command according to a predetermined procedure, and determines the focus adjustment and aperture control operations, as well as the operation status of each part of the lens (the driving status of the focusing optical system, the driving status of the diaphragm, etc.) from the output signal DLC. and various parameters (open F number, focal length, coefficient of defocus amount vs. movement amount of the focusing optical system, etc.).

This embodiment shows an example of a zoom lens, and when a focus adjustment command is sent from a camera, the focus adjustment motor LTMI is activated according to the driving amount and direction sent at the same time.
I is driven by signals LM and LMR to move the optical system in the optical axis direction and perform focus adjustment. The amount of movement of the optical system is monitored by the pulse signal 5ENCF of the encoder circuit ENCF, and is calculated by a counter in LPR3, and when the specified movement is completed, the control circuit LPR3 itself in the lens sets the signals LMF and LMR to L''. brake the motor LVTR.

Therefore, once the focus adjustment command is sent from the camera, PH1 does not need to be involved in lens driving at all until the lens driving is completed. Furthermore, the configuration is such that it is possible to send the contents of the counter to the camera if there is a request from the camera.

When an aperture control command is sent from the camera, a stepping motor DMTR, which is known for driving an aperture, is driven in accordance with the number of aperture stages sent at the same time. In addition,
Stepper motors are open-controlled and do not require an encoder to monitor operation.

ENCZ is an encoder circuit attached to the zoom optical system, and the in-lens control circuit LPR3 is the encoder circuit EN.
The zoom position is detected by inputting the signal 5ENCZ from CZ. Lens parameters at each zoom position are stored in the in-lens control circuit LPR3, and when a request is received from the PRS on the camera side, parameters corresponding to the current zoom position are sent to the camera.

The operation of the camera with the above configuration will be explained according to the flowcharts from FIG. 3 onwards.

When a power switch (not shown) is turned on, power supply to the PRS is started, and the PR3 starts executing the sequence program stored in the ROM.

FIG. 3 is a flowchart showing the overall flow of the above program.

When the execution of the program is started by the above operation, the switch SW is turned on by pressing the first stage of the release button in step (002) after passing through step (001).
When the state of SWI is detected and SWI is off, the process moves to step (003), where all control flags and variables set in the RAM in PR3 are cleared and initialized.

The above steps (002) and (003) are the switch SWI
It will run repeatedly until it is turned on or the power switch is turned off. When the switch SWI is turned on, the process moves from step (002) to (004).

In step (004), a "photometering" subroutine for exposure control is executed. PRS inputs the output 5spc of the photometric sensor SPC shown in Fig. 1 to the analog input terminal,
Perform A/D conversion, calculate the optimal shutter control value and aperture control value from the digital photometry value, and set each value to R.
Store it at a predetermined address in AM. During the release operation, the shutter and aperture are controlled based on these values.

Subsequently, in step (005), an "image signal input" subroutine is executed. The flow of this subroutine is shown in FIG. 4, where PRS is a line sensor device S for focus detection.
Image signals are input from the NS. Details will be described later.

In the next step (006), a "focus detection" subroutine is executed, and the defocus amount DEF of the photographing lens is calculated based on the input image signal. The specific calculation method is disclosed in Japanese Patent Application No. 160824/1982, and so a detailed explanation will be omitted.

In the next step (007), a "prediction calculation" subroutine is executed. The "prediction calculation" subroutine is the above formula (9)
(10) The lens drive amount correction shown in (11) is performed, and the flow thereof is shown in FIG.

Subsequently, in step (008), a "prediction determination" subroutine is executed. The "predictive determination" subroutine performs the two-step determination described above, and its flow is shown in FIG.

In the next step (009), a "lens drive" subroutine is executed, and the lens is driven based on the defocus amount corrected in the previous step (007) or the detected defocus amount DL. The flow of the "lens drive" subroutine is shown in FIG.

After the lens drive is completed, the process moves to step (002) again, and steps (004) to (009) are repeatedly executed until the switch SWI is turned off, so that preferable focus adjustment is performed even for a moving subject.

Note that the switch SW2, which is turned on by pressing the release button in the second step, is connected to the interrupt input terminal of the PRS, as explained earlier, and when the switch SW2 is turned on, no matter which step is being executed, an interrupt is generated. Although the camera is configured to immediately proceed to the step of the release operation, the release operation is not directly related to the present invention, so its explanation will be omitted.

Next, the "image signal input" subroutine shown in FIG. 4 will be explained.

"Image signal input" is an operation executed at the beginning of each cycle of focus adjustment operation, and when this subroutine is called, in step (102) via step (101), PR3 itself has Timer value TIM of self-running timer
By storing ER in the storage area TN on the RAM, the start time of the focus adjustment operation is memorized.

In the next step (103), the lens drive amount correction formula (9
) (10) Time interval TMi-2,TM in (It)
Update TM1 and TN2 corresponding to i-1. Before executing step (103), TMI, TN2 contains the time intervals TMi-2, T
Mi-1 is stored, and TNI stores the time when the previous focus adjustment operation was started.

Therefore, TN2 represents the time interval of the focus adjustment operation from the time before the previous time to the time before the previous time, and TN-TNI represents the time interval of the focus adjustment operation from the time before the previous time to the time of the present time.
Storage area TMI, TN on RAM corresponding to Mi-]
It is stored in 2. Then, the current time TN is stored in TNI for the next focus adjustment operation.

Now, in the next step (104), the line sensor device SN
Let S start accumulating a light image. Specifically, PH1 sends an "accumulation start command" to the sensor drive circuit SDR by communication, and in response to this, the circuit SDR sets the clear signal CLR of the photoelectric conversion element section of the line sensor device SNS to to start charge accumulation.

In step (105), the free-running timer value is stored in the variable TI to memorize the current time.

In the next step (106), the input INTEND of PH1
Detects the state of the terminal and checks whether storage has finished.

The sensor drive circuit SDR outputs the signal INTE at the same time as the start of accumulation.
ND is set to L°, the signal 5AGC from the line sensor device SNS is monitored, and when the signal 5AGC reaches a predetermined level, the signal INTEND is set to °H°, and at the same time, the charge transfer signal SH is set to "H" for a predetermined time. It has a structure in which charges in the photoelectric conversion element section are transferred to the CCD section.

In step (106), if the INTEND terminal is °゛H°', it means that the accumulation has finished, and the process moves to step (110), and if it is "L", it means that the accumulation has not finished yet, and the process goes to step (]07). Move to.

In step (107), the timer value TIME of the free-running timer is
The time TI stored in step (1135) is subtracted from I(, and stored in the variable TE. Therefore, the time from the start of accumulation to each individual, the so-called "accumulation time" is stored in TE.

In the next step (108), TE and constant NAX INT
If TE is less than MAX INT, step (
The process returns to step 106) and waits for the completion of accumulation again. TE is MA
When the value exceeds X INT, the process moves to step (109) to forcibly terminate the accumulation. The forced termination of zero accumulation is executed by sending an "accumulation termination command" from PH1 to the sensor drive circuit SDR.

When the sensor drive circuit SDR receives the "accumulation end command" from PH1, it keeps the charge transfer signal SH high for a predetermined period of time.
The accumulated charges in the photoelectric conversion section are transferred to the CCD section.

The sensor accumulation ends in the flow up to step (+09).

In step (110), the image signal O3 of the line sensor device SNS is amplified by the sensor drive circuit SDR, and the signal AO3 is A/D converted and the digital signal is stored in the RAM. To explain in more detail, the sensor drive circuit SDR generates the CCD drive clock φ1. in synchronization with the clock CK from PH1. φ2 is generated and given to the control circuit 5SCNT inside the line sensor device SNS, and the device SNS generates φ1. φ
2 drives the CCD section, and the charges within the CCD are outputted in time series as an image signal O3. After this signal is amplified by an amplifier inside the sensor drive circuit SDR, it is input to the analog input terminal of PH1 as an image signal AO3.

PH1 synchronizes with the clock C that it outputs, and
A/D conversion is performed, and the digital image signals after A/D conversion are sequentially stored at predetermined addresses in the RAM.

After inputting the image signal in this way, step (
At step 111), the "image signal input" subroutine is returned.

Next, the "lens drive" subroutine shown in FIG. 5 will be described.

When this subroutine is called, step (202
) to communicate with the lens and send two data rsJrP
Manpower THJ. rsJ is the "coefficient of the amount of movement of the focusing optical system versus the amount of movement of the image plane" of the photographing lens. That is, it represents the amount of movement of the image plane of the photographic lens when the focusing optical system of the photographic lens is moved by a unit length in the optical axis direction. For example, in the case of a single lens that extends entirely, the entire photographing lens corresponds to the focusing optical system, and the movement of the focusing optical system is equivalent to the movement of the image plane of the photographing lens, so rs = IJ. , in the case of a zoom lens, "s" changes depending on the position of the zoom optical system.

rPTHJ is the amount of movement of the focusing optical system LNS per output pulse of the encoder circuit ENCF, which is linked to the movement of the focusing optical system LNS in the optical axis direction.

Therefore, the defocus amount DL to be adjusted.

From the above rsJ and rPTHJ, the value obtained by converting the movement amount of the focusing optical system into the number of output pulses of the encoder circuit, the so-called lens drive amount FP, is given by the following equation.

FP=　D　L-s　/　PTH Step (203) executes the above equation as is.

In step (204), the lens drive amount FP obtained in step (203) is sent to the lens to command the focusing optical system to be driven.

In the next step (205), it is detected whether or not the driving of the lens driving amount FP commanded in step (204) is completed by communicating with the lens, and when the driving is completed, step (215)
) and return to the "lens drive" subroutine.

Next, the "prediction calculation" subroutine shown in FIG. 6 will be described.

In the present invention, the correction calculation formulas (9) (10) (
Replace the defocus amount in 11) with the lens movement amount and calculate.

If the latest detected defocus amount is DEF and the above lens coefficient is S, then DF i =DEF ・s After replacing the above equation (12), equations (9) (10) (
11) By performing the recurrence type correction formula, a corrected lens driving amount DLi is obtained.

In steps (302) and (303), data is updated for the current correction calculation. That is, equation (9) (
10) and (11) are expressed in the form of recurrence formulas, and use data from a plurality of past times from the time point at which the correction calculation is executed. In step (302), the data for converting the detected defocus amount into the lens movement amount is updated, and in (303), the data for converting the corrected defocus amount to the lens movement amount to be driven by the lens is updated.

In the next step (304), a value of 7M2 is stored in TM3 corresponding to the time interval TMi from this time to the next focus adjustment operation. That is, as stated in the explanation of equation (11), the time interval TM of the focus adjustment operation from the previous time to this time
2 is assumed to be the time interval TM3 from this time to the next time.

In step (305), the lens coefficient rsJ is input from the lens, and in the next step (306), the amount of defocus is converted into the amount of lens movement expressed by equation (12). Formula (9
) (10) Since (11) is a recurrence form, by performing the calculation of equation (12) on the currently detected defocus amount DEF, conversion of all defocus amounts to lens movement amounts is achieved.

In the next step (307), a check is made to see if the data for performing the predictive calculation is complete. If the data of the past two focus adjustment operations and the current distance measurement results are not complete, proceed to step (308) and use the latest defocus amount DEF as is to determine the defocus amount D that should be used to drive the lens.
L, the process directly proceeds to step (313), and the "prediction calculation" subroutine is returned.

If there is enough data to perform the predictive calculation, the process moves to step (309). Step (309) executes Equation (9), (310) executes Equation (1o), and (311) executes Equation (11) to obtain the lens movement amount conversion value DLS of the defocus amount to be driven by the lens. .

Then, in step (312), the lens movement amount DLS is calculated by calculating DL=DLS/S.
For the "lens drive" subroutine, the defocus amount DL is converted again, and the "prediction calculation" subroutine is returned at step (313).

Next, the "prediction determination" subroutine shown in FIG. 7 will be described.

In step (402), a check is made to see if there are enough pigs to perform the prediction calculation. If the data of the past two focus adjustment operations and the current distance measurement results are not available, the latest defocus amount DEF is the defocus amount OL that should be used to drive the lens, so it can be used as it is at step (41).
The process moves to 2) and returns to the "prediction determination" subroutine.

If enough data is available for the predictive calculation and the predictive calculation has been performed, the process moves to step (403). Step (403) uses equation (12), step (404) uses equation (13) mentioned above, and step (405) uses equation (15).
are executed respectively, and first the subject image plane movement speeds V12 and V
23, and find the value Vc necessary for the first stage determination.

In the following step (406), check the sign of Vc and set V12.
, V23. If Vc is negative, it is assumed that the direction has changed and the process moves to step (408). If Vc is positive, the process moves to step (407), where Vc is compared with the first-stage determination reference value Vp to check whether the rate of change in the image plane movement speed is appropriate. If Vc exceeds Vp, it is determined that the rate of change is inappropriate, and step (4)
08) to perform the second stage determination. If Vc does not exceed Vp, it is assumed that the rate of change in the image plane movement speed is appropriate, and the process directly proceeds to step (412) to drive the lens with the calculated correction amount, and returns to the "prediction determination" subroutine.

In step (408), the value Vd required for the second stage determination is determined as the absolute value of equation (14). Next step (40
In step 9), the second step judgment reference value (■0) is compared with Vd to check the amount of change in the image plane movement speed. If Vd does not exceed Vc, it is assumed that the amount of change is appropriate, and the lens is driven with the calculated correction amount, so the process moves to step (412) and returns to the "prediction determination" subroutine.

If Vd exceeds ■○, it is considered inappropriate in terms of the amount of change, and the lens is not driven with the calculated correction amount.
In step (410), the latest defocus amount DEF is directly set as the defocus amount DL for driving the lens. In the following step (411), all past prediction data is discarded and the prediction is restarted from the beginning, and in step (412)
Then, the "prediction judgment" subroutine is returned.

According to this embodiment, in order to focus even on a moving subject, in a method that predicts the defocus change caused by the movement of the subject and corrects the lens drive amount, correction is performed using the determined correction value. Since the decision as to whether or not to perform the correction is made in two stages: the rate of change and the amount of change in the image plane movement speed, it is effective in preventing erroneous focus adjustment operations without compromising the original purpose of correction. It becomes possible to make a judgment,
Even fast-moving subjects can be accurately tracked, allowing for in-focus photography.

(Correspondence between the invention and the embodiment) In this embodiment, the part that performs the operations of steps 309 to 312 in FIG. 6 is the correction means of the present invention, and the part that executes each step of FIG. Equivalent to.

(Modified example) In this embodiment, the change in the image plane value due to the movement of the subject is approximated by a quadratic function, but the present invention is not limited to this, and the -order function is approximated by a quadratic function. It goes without saying that higher-order functions or even other appropriate functions can also be applied.

In addition, in this embodiment, if the judgment is inappropriate, the past data is immediately discarded and the correction is restarted from the beginning. It is also possible to have an opportunity to detect ranging data that can be appropriately corrected by redoing only the above steps.

(Effects of the Invention) As explained above, according to the present invention, the defocus amount from the focus detection means is determined using the rate of change and amount of change in the moving speed of the object image plane position obtained in the process of determining the correction amount. A determination means is provided for determining whether or not to add the correction value obtained by the correction means to In addition, since the correction is performed based on the rate of change, it is possible to perform focus adjustment that accurately follows even fast-moving objects without compromising the original purpose of correction.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention, FIG. 2 is a diagram for explaining an overview of one embodiment of the present invention, and FIGS. 3 to 7 are respective diagrams of one embodiment of the present invention. FIG. 8 is a diagram for explaining the focus adjustment operation of the conventional device, and FIG. 9 is a diagram for explaining the outline of the portion of the conventional device according to the present invention. PR3...In-camera control circuit, SNS...
... Line sensor device, LTMR ... Focus adjustment motor, LMTR ... Motor, ENCF ...
... Encoder circuit, LCM ... Lens communication buffer circuit.

Claims (1)

[Claims] (1) a focus detection means for repeatedly detecting the amount of defocus from a subject passing through the photographic lens at predetermined time intervals; a lens driving means for driving the focus adjustment optical system of the photographic lens based on the amount of defocus; a correction means for correcting the amount of defocus to be applied to the lens driving means in consideration of the focus detection results of a plurality of past focus detections including the current one of the focus detection means and the time interval of at least one past focus detection operation; In the automatic focus adjustment device equipped with the above, the defocus amount determined by the focus detection means is determined by the defocus amount determined by the correction means using the rate of change and amount of change in the moving speed of the object image plane position obtained in the process of determining the correction amount. An automatic focus adjustment device characterized by comprising a determining means for determining whether or not to add a correction value.