JPH01200315A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To secure a high following performance while estimated errors are prevented by obtaining the image plane position of an object after a prescribed time has passed, based on a defocus amount, the result of iteration, with the aid of a several-degree function and correcting the highest-degree coefficient. CONSTITUTION:In a several-degree function used for predictive calculation, the highest term is corrected. Namely, the image plane position that a camera recognizes is calculated from the detected defocus amount and a lens driving amount, however, they have errors. Consequently, the image plane position recognized by a camera also has an error, and a predictive error in predictive AF is amplified and turns into a nonpermissible amount. Then, a secondary term accounting for the most of a predictive error is corrected to reduce a predictive error substantially. Thus, AF is impervious to errors in focal point detection and in lens driving, whereby highly accurate following and correcting are possible.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an automatic focus adjustment device used in cameras and the like.

[Conventional technology]

Conventionally, most automatic focusing systems for eye reflex cameras were
By repeating the cycle of focus detection (sensor signal input, focus detection calculation), and lens drive, it is possible to bring the subject into focus. 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 focusing method aimed at solving the above problems, the present applicant has proposed Japanese Patent Application No. 62-263728.

The gist of the method disclosed in this proposal is to calculate the relationship between the image plane position and time caused by the movement of the subject into one by taking into consideration the detected defocus amount, lens drive amount, and time interval of each cycle in each cycle. This is an attempt to correct the lens driving amount by approximating the following function and quadratic function, and is expected to improve the above problem.

[Problems to be Solved by the Invention] The present invention relates to further improvements to focus adjustment using the above prediction method, and eliminates focus detection errors caused by focus detection operations, lens drive operations, and incorrect lens drive based on lens drive errors. It is intended to prevent this.

Incorrect lens driving due to the above error will be explained below.

FIG. 2 is a diagram for explaining the above-mentioned lens drive correction method. The horizontal axis in the figure represents time t, and the vertical axis represents the image plane position X of the subject.

The curve x(t) represented by a solid line means the image plane position at time t of a subject approaching the camera in the optical axis direction when the photographing lens is at infinity. 2(1) means the photographing lens position at time t, and in-focus occurs when x(t) and f(t) match.And [t+, t+'] is the focus detection operation time, [t I' , t +++ ] indicates the lens driving operation time. Also, in the example shown in the figure, it is assumed that the image plane position changes according to a quadratic function (at''+bt+c). That is, at time t3, the current and past three image plane positions (t+, x+)(t2
+ X2 ) (t3 * time, release time lag: time from when a release command is issued until exposure starts).

However, what the camera can actually detect is the image plane position xl.
l Instead of x2 + x3, the defocus amount DF,
.

DF2. DF3, and lens drive amounts DL, DL2 in terms of image plane movement amount. The time t4 is only a future value, and in reality, it is a value that changes as the storage time of the storage type sensor changes depending on the subject brightness, but for the sake of simplicity, it is assumed as follows. do.

t4-t3 = TL = 7M2+ (Release time lag) (1) Under the above assumptions, the lens drive amount DL3 calculated from the focus detection result at time t3 is determined as follows.

x(t)=at”+bt+c (
2) Then, considering (1+, I!1) in the figure as the origin, t1==o xl=DF,
(3) t2 = TM1 x2 = DF2
+ DLI (4) t3=TM1+TM2
x3=DF3+DL1+DL2 (5) (2) and (3)
, (4), and (5) by substituting equations a.

When calculating b and c, c = DPI
(8) Therefore, the lens drive amount DL3 converted to the image plane movement amount at time t4 is: DL3=x4-13 =x4-x3+DF3=a [(TM1+TM2+TL)''-(TMl+T
M2)')+b-TL+DF3 (9)

Next, erroneous predictions due to focus detection errors and lens drive errors will be explained using FIG. 3.

FIG. 3 shows the relationship between the image plane position and time, and the solid line indicates the position of the image plane that actually moves.

That is, (tto x+) (t21 X2)
Quadratic function x = a t” + b t + c passing through (ji+X3)
(10) can be approximated.

On the other hand, the image plane position recognized by the camera is calculated from the detected defocus amount and lens drive amount, but since there is an error in this defocus amount and lens drive amount, Errors also occur in the image plane position recognized by the camera.

That is, XI', X2', and X3' are obtained as shown in the following equation.

x,′:I)F,′=DF1+δt,
(n)x2'==I)F'2' +D
t,,':I)F'2+DL1+δf2+δI! ,
(12)x3' = DF3'+DL1' +DL2
'=DF3 +DL1 +DL2+δf3+δ11+
δl12(13) Here, DF,' , DF2', DF3'
is the detected defocus amount DL, ', DL2' is the lens drive amount detected by the camera, and DF, DF2. DF3 is the true defocus amount DL,
DL2 is the actual lens driving amount, and δf1. δf2+δf3 is the focus detection error δ11. δ
12 is a lens drive error.

Then, the difference between the image plane position recognized by the camera and the actual image plane position is δ1. δ2. δ3 is as follows.

δ1 ``XI' xl = δf,
(14) δ2 = X2' X2 ”δf2+δ11
(15) δ3 = X3' x3 = δf3+δl
, +δ12(16) and (tl + X+')
The quadratic function passing through (t21 X2') (t3+X3') is x = a't" + b' t + c'
(17), and a prediction error of δp occurs between the lens position X4' found using this function and the image plane position x4 at t4.

This prediction error δp becomes an error amount several times the focus detection error or lens drive error.

In this way, the focus detection error and lens drive error, which did not pose a problem with the conventional focus adjustment device, are amplified several times in the prediction error of the predictive AF that performs tracking correction, resulting in an unacceptable amount.

[Means for solving problems]

The present invention aims to solve the above problems,
By correcting high-order terms among several-order functions used in predictive calculations, the influence of errors occurring in the focus detection system or lens drive system is reduced, and prediction accuracy is improved.

〔Example〕

FIG. 4 is a circuit diagram showing an embodiment of a camera equipped with an automatic focusing device according to the present invention.

In the figure, PRS is a camera control device, and is, for example, an l-chip microcomputer having an internal CPU (central processing unit), ROM, RAM, and A/D conversion function. The computer PR3 performs a series of camera operations such as an automatic exposure control function, an automatic focus detection function, and film winding according to a camera sequence program stored in the ROM. For this purpose, the computer PR3 uses the synchronous communication signals 5O9SI, 5CLK, and the communication selection signal CL.
The CM, C3DR, and CDDR are used to communicate with peripheral circuits and lenses within the camera body to control the operations of each circuit and lens.

SO is a data signal output from computer PR3,
Sl is a data signal input to the computer PR3, 5
CLK is a synchronization clock for signals So and SI.

LCM is a lens communication buffer circuit that supplies power to the lens power supply terminal when the camera is in operation, and when the selection signal CLCM from the computer PR3 is at a high potential level (hereinafter abbreviated as ゛H°), it supplies power to the lens power terminal. Serves as an inter-lens communication buffer.

Computer PRS sets CLCM to high and S CL
When predetermined data is sent from SO in synchronization with K, L
CM is sent via the camera-lens interface, 5CLK, So
The respective buffer signals LCK and DCL are output to the lens. At the same time, a buffered signal of the signal DLC from the lens is output to Sl, and PRS inputs lens data from Sl in synchronization with 5CLK.

SDR is a drive circuit for the line sensor device SNS for focus detection, which is composed of a CCD, etc., and the signal C3DR is H°.
is selected and PR is performed using So, Sl, 5CLK.
Controlled from S.

The signal CK is the COD driving clock φ1. This 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 O8 of the SNS is a time-series image signal synchronized with the clocks φl and φ2, and after being amplified by the amplifier circuit in the SDR, it is outputted to the PH1 as AO5. PH1 is AO
3 is input from the analog input terminal, is A/D converted by the internal A/D conversion function in synchronization with CK, and is sequentially stored at a predetermined address in the RAM.

Same < 5AGC, which is the output signal of SNS,
trol) sensor, is input to the SDR, and is used for SNS storage control.

SPC is a photometric sensor for exposure control that receives light from the subject through the photographic lens, and its output of 5spc is P
The signal is input to the analog input terminal of H1, and after A/D conversion is used for automatic exposure control (AE) according to a predetermined program.

DDR is a switch detection and display circuit, and the signal C
Selected when DDR is “H”, So, Sr, 5
Controlled from PH1 using CLK. That is, based on the data sent from PH1, the display member DS of the camera
The P display can be switched, and the on/off status of the switch SWS linked to various camera operation members can be changed via communication.
Notify H1.

The switches SWI and SW2 are switches linked to a release button (not shown), and when the release button is pressed to the first stage, SWI is turned on, and when the release button is pressed to the second stage, SW2 is turned on. As will be described later, the computer PR3 performs photometry and automatic focus adjustment when the SWI is turned on, and
Exposure control and film winding are performed using 2-on as a trigger. Note that SW2 is connected to the "interrupt input terminal" of the microcomputer PR8, and even if the program is being executed when the SWI is on, an interrupt is generated by turning on the SW2, and the program can immediately proceed 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/reverse rotation control is performed by each of the drive circuits MDRI and MDR2. PH1 to MDRI.

Signals MIF, MIR, M2F input to MDR2
.

M2R is a signal for motor control.

MCI and MG2 are magnets for starting the movement of the front and rear shutter curtains, respectively, and are energized by signals SMGI, 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 thereof will be omitted.

The signal DCL input to the in-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.

LPR8 analyzes the instruction according to a predetermined procedure,
It performs focus adjustment and aperture control operations, and outputs various lens parameters (open F number, focal length, coefficient of defocus ratio versus extension amount, etc.) from the output DLC.

In the embodiment, an example of a zoom lens is shown, and when a focus adjustment command is sent from a camera, the focus adjustment motor LMTR is activated according to the driving amount and direction sent at the same time.
is driven by signals LMF 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 counted by a counter in the LPR3, and when the predetermined movement is completed, the LPR3 itself outputs the signals LMF and LM.
'L' for R.

to brake motor LMTR.

Therefore, once the focus adjustment command is sent from the camera, the control device PR3 within the camera does not need to be involved in lens driving at all until the lens driving is completed.

Further, when an aperture control command is sent from the camera, a stepping skewer motor DMTR, which is known for driving an aperture, is driven in accordance with the number of aperture stages sent at the same time.

ENCZ is an encoder circuit attached to the zoom optical system, and LPR3 receives a signal 5ENCZ from ENCZ to detect the zoom position. Lens parameters at each zoom position are stored in the LPR3, and when a request is made from the camera side PH1, 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 shown in FIG. 5 and subsequent figures.

When a power switch (not shown) is turned on, power supply to the microcomputer PR3 is started, and PH1 starts executing the sequence program stored in the ROM.

FIG. 5 is a flow chart showing the overall flow of the above program. When the program execution starts with the above operation, it passes through step (001) and then step (002).
), the state of the switch SWI, which is turned on by pressing the first step of the release button, is detected, and when SWl is off, the process moves to step (OOa), and the R in PRS is detected.
Clear and initialize all control flags and variables set in AM.

The above steps (002) and (003) are the switch SWI
is turned on or the power switch is turned off (repeatedly executed. When SW1 is turned on, the process moves from step (002) to step (005).

In step (005), a "photometering" subroutine for exposure control is executed. PH1 inputs the output 5spc of the photometry sensor SPC shown in Fig. 4 to the analog input terminal, performs A/D conversion, calculates the optimal shutter control value and aperture control value from the digital photometry value, Each is stored at a predetermined address in RAM. During the release operation, the shutter and aperture are controlled based on these values.

Subsequently, in step (006), an "image signal input" subroutine is executed. The flow of this subroutine is shown in FIG. 6, and PH1 inputs an image signal from the focus detection sensor device SNS. Details will be described later.

In the next step (007), 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. 61-16082 by the applicant.
Since it is disclosed in Publication No. 4 etc., detailed explanation will be omitted.

In step (008), a "prediction calculation" subroutine is executed. The "prediction calculation" subroutine is for correcting the lens drive amount, and its flow is shown in FIG.

Subsequently, in step (009), a "lens drive" subroutine is executed, and the lens is driven based on the lens drive amount DL corrected in the previous step (008). The flow of this "lens drive" subroutine is shown in FIG. After lens driving is completed, step (002) is performed again.
' until SWl is turned off or switch SW2 (not shown) is turned on, steps (005) to (00
Step 9) is repeatedly executed to achieve preferable focus adjustment even for a moving subject.

Now, the release button is pushed in further and the switch S
When W2 is turned on, the interrupt function immediately moves to step (010) to start the release operation, regardless of which step it is in.

In step (011), it is determined whether or not lens driving is being executed. If driving is in progress, the process moves to step (012), a driving stop command is sent to the lens, the lens is stopped, and step (013) is performed. If the lens is not being driven, the process immediately advances to step (013).

In step (013), the quick return mirror of the camera is raised. This is executed by controlling the motor MTR2 using the motor control signals M2F and M2R shown in FIG. In the next step (014), the aperture control value already stored in the photometry subroutine of the previous step (005) is sent to the lens to cause the lens to perform aperture control.

Whether or not the mirror up and aperture control in steps (013) and (014) have been completed is detected in step (015), and mirror up can be confirmed using a detection switch (not shown) attached to the mirror. For aperture control, it is confirmed via communication whether the lens has been driven to a predetermined aperture value. If either one is not completed, the process waits at this step and continues to detect the status. When it is confirmed that both controls have been completed, the process moves to step (016).

In step (016), the shutter is controlled using the shutter control value already stored in the photometry subroutine of the previous step (005), and the film is exposed.

When the shutter control is completed, in the next step (017), a command is sent to the lens to open the aperture, and then in step (018), the mirror is lowered. Similar to mirror up, mirror down is executed by controlling motor MTR2 using motor control signals M2F and M2R.

In the next step (019), similarly to step (015), wait for the mirror down and aperture opening control to be completed.When both mirror down and aperture opening control are completed, step (019)
20).

In step (020), the motor MT is controlled by appropriately controlling the motor control signals MIF and MIR shown in FIG.
By controlling R1, one frame of film is wound.

The above is the sequence of the camera that performed predictive AF.

Next, the "image signal input" subroutine shown in FIG. 6 will be explained.

"Image signal input" is the first operation to be executed in a new focus detection operation, and when this subroutine is called, the process proceeds to step (101) and then to step (102). By storing the timer value TIMER of the self-running timer in the storage area TN on the RAM, the start time of the focus detection operation is stored.

In the next step (103), the lens drive amount correction formula (6
) (7) Time interval TIVln-2,TM in (9)
Update TMI 7M2 corresponding to n-+. Before executing step (103), TMI, 7M2 includes time intervals T M n-2, T
M n-1 is stored, and TNI stores the time when the previous focus detection operation was started.

Therefore, 7M2 represents the time interval of the focus detection operation from the previous time to the previous time, and TNI-TN represents the time interval of the focus detection operation from the previous time to the current time, and this is T Mn-2,T in equations (6), (7), and (9).
Storage areas TMI and TM2 on the RAM corresponding to Mn-+
It is stored in . Then, the current time TN is stored in TNI for the next focus detection operation. That is,
In step (103), the focus detection operation times from the previous time to the previous time and from the previous time to the current time are always stored in the storage areas TMI and TM2.

Now, in the next step (104), the sensor device SNS is caused to start accumulating optical images. Specifically, the microcomputer PR5 sets C3DR to H, and the sensor drive circuit SDR
In response to this, the SDR sends an "accumulation start command" as an SO via communication, and in response to this, the SDR changes the clear signal CLR of the photoelectric conversion element section of the sensor device SNS to L to start accumulating charges.

In step (105), the timer value of the free-running timer is set as a variable T.
I to store the current time.

In the next step (106), the state of the input INTEND terminal to the computer PR3 is detected, and it is determined whether or not the storage has been completed. The sensor drive circuit SDR sets the signal INTEND to L' at the same time as the start of accumulation, monitors the AGC signal 5AGC (signal representing the accumulation amount) from the sensor device SNS, and when the 5AGC reaches a predetermined level, changes the signal INTEND to L'.
It has a structure in which the charge in the photoelectric conversion element section is transferred to the CCD section by setting ND to H' and simultaneously setting the charge transfer signal SH to "H" for a predetermined period of time.

In step (106), if the INTEND terminal is H°, it means that the storage has been completed, and the process moves to step (110); if it is L°, it means that the storage has not finished yet, and the process moves to step (107).

In step (107), the timer value TIME of the free-running timer is
The time TI stored in step (105) is subtracted from R and stored in the variable TE. Therefore, the time from the start of accumulation to this point, the so-called accumulation time, is stored in TH. In the next step (108), TE and constant MAX
INT is compared, and if TE is less than MAXINT, the process returns to step (106) and waits for the completion of accumulation again. When TE exceeds MAXINT, the process moves to step (109) and the accumulation is forcibly terminated.

The forced storage termination is executed by sending an "accumulation termination command" from the computer PR3 to the circuit SDR using the above communication signal. When the SDR receives an "accumulation end command" from the PH1, it sets the charge transfer signal SH to ゛H° for a predetermined period of time and transfers the charges in the photoelectric conversion section to the CCD section. Step (
The sensor accumulation ends with the flow up to step 109).

In step (110), the image signal O8 of the sensor device SNS is
A/D of signal AO3 amplified by sensor drive circuit SDR
Performs conversion and stores the digital signal in RAM. To explain in more detail, the SDR uses the COD driving clock φ1. in synchronization with the clock CK from PH1. φ2 is generated and given to the control circuit inside the SNS, and the SNS generates φ1. φ2
The CCD unit is driven by the CCD unit, and the charges in the CCD are output in time series from the output O8 as an image signal. After this signal is amplified by an amplifier inside the SDR, it is input as AO3 to the analog input terminal of PH1. The PH1 performs A/D conversion in synchronization with the clock CK that it outputs, and sequentially stores the digital image signals after A/D conversion at predetermined addresses in the RAM.

After inputting the image signal in this way, step (1
At step 11), the "image signal input" subroutine is returned.

FIG. 7 shows a flowchart of the "lens drive" subroutine.

When this subroutine is executed, step (202)
communicates with the lens at
Enter THJ. rSJ is the [coefficient of the amount of defocus versus the amount of protrusion of the focusing lens] specific to the photographic lens,
For example, in the case of the entire (extending type single lens), S = 1 because the entire photographing lens is a focusing lens, and in the case of a zoom lens, S changes depending on each zoom position.rPTHJ is the focusing lens This is the amount by which the focusing lens is extended per one pulse output from the encoder ENCF, which is linked to the movement of the LNS in the optical axis direction.

Therefore, the defocus amount DL to be adjusted, the above S, P
The value obtained by converting the amount of protrusion of the focusing lens into the number of output pulses of the encoder using TH, the so-called lens drive fiF
P will be given by the following equation.

FP=DLXS/PTH Step (203) executes the above equation as is.

In step (204), F obtained in step (203)
P is sent to the lens to command the driving of the focusing lens (or the entire photographing lens in the case of a fully extending single lens).

In the next step (205), it is detected whether or not the driving of the lens driving amount FP commanded in step (206) is completed by communicating with the lens, and when the driving is completed, step (206)
) and return to the "lens drive" subroutine.

In addition, to detect the end of lens driving, as described above, the driving amount FP is input to the circuit LPR3, and when the lens is driven, the pulse 5ENCF of the encoder circuit ENCF is counted by the counter in the LPRS, and this counted value is the above-mentioned value. F
A determination as to whether or not P matches is made in the circuit LPR3, and the output state of LPR3 when the counted value and FP match is detected through the communication in step (205) above, and step (206) This is a transition to

Next, the flow of the "prediction calculation" subroutine will be explained with reference to FIG. FIG. 1 shows the flow of the "prediction calculation" subroutine, which calculates the lens drive amount taking into account the release time lag. Step (302) (
'303), the data for the current prediction calculation is updated.

That is, in step (302), the data in the memory DF2 is input to DF. The previous defocus amount is input to the memory DF2 before this subroutine is executed, but at the time the current subroutine is executed, the contents of DF2 become the previous defocus amount. So, input this into memory DF and save it to memory D.
The previous defocus amount is always stored in F.

Also, input the contents of the memory DF3 to DF2 so that DF2 always stores the previous defocus amount, and stores the current detected defocus fi DEF in DF3 so that DF3 always stores the current defocus amount. I am doing it.

Further, in step (303), the data in the memory DL2 is input to the memory DL, and the lens driving amount data from the previous time is always stored in the memory DL. The data DL is also input to the memory DL2. Data 〇L is the previous driving amount data, and the memory DL2 always stores the lens driving amount data performed immediately before.

In the above steps (302) and (303), the current defocus amount and lens drive amount data from the past multiple times are updated and stored in each memory.

In step (304), a time lag TL is calculated.

This calculation is executed by calculating the sum of the data in the storage area TM2 and the release time lag TR.

As mentioned above, the memory area TM2 stores the focus detection operation time from the previous time to the current time, and the current focus detection operation time is assumed to match the previous focus detection operation time. Find time lag TL=TM2+TR.

In steps (305) and (306), each memory DF.

~DF3. DL,,DL2. Based on the data stored in TM, 7M2, a and b in equations (6) and (7)
Find A and B that represent the terms.

In the next step (307), a correction coefficient TF is determined in a subroutine to be described later, and the process moves to step (308).

In this step (308), based on the data in each memory and the calculated values in steps (304) to (306),
9) Find the calculated value of the formula, and add the above correction coefficient TF to this calculated value.
The multiplied value is calculated to obtain the lens drive amount DL in terms of the current image plane movement amount. After this, the process returns to step (309).

When the prediction calculation is performed in this way, step (009)
At this point, the lens is driven as described above, and the lens is moved to a position where the image plane positions match.

Next, the flow of the "correction coefficient calculation" subroutine will be explained.

FIG. 8 shows the flow of "correction coefficient calculation", and in step (402), the ratio between the focus detection operation time interval and the time lag used for prediction is TX = (TM).

+7M2)/(2・TL) for each storage area TM,,TM
2 data and T obtained in step (304) above
Calculate based on L and proceed to the next step.

In step (403), a coefficient TF for correcting the quadratic term is calculated using the TX obtained in step (402),
Return.

In this embodiment, if the release time lag is constant, T
Focusing on the fact that when the XO value is small, the focus detection operation time interval becomes short, we set the correction coefficient TF to be small (0<TF≦1).
When TX is large, reducing TF excessively has a negative effect, so when TX is large, TF approaches 1 (
I set it like this.

As described above, in the present invention, in step (308), (9)
Since the correction is made to reduce the coefficient of the quadratic term in the lens drive amount determined by the equation (9), it is possible to reduce the error in the lens drive amount based on equation (9).

FIG. 9 shows the effect when the present invention is actually implemented.

In this figure, the solid line is assumed to be the image plane position that is actually moving due to the movement of the subject, and δ1.
When an error of δ2 occurs, the prediction function becomes like a dashed-dotted line, and the prediction error δe becomes δ1. It is approximately 11 times larger than δ2.

On the other hand, the quadratic term is a correction coefficient (0.6 in this case)
By multiplying and correcting, the prediction function becomes as shown by the broken line, and the prediction error δe' is reduced to about 1/8 of the unmeasured prediction error δe.

As described above, the correction according to the present invention is effective in preventing prediction errors, which occur due to errors in the focus detection system and lens drive system, and errors occur between the image plane position recognized by the camera and the actual image plane position, which causes prediction errors. By correcting the quadratic term, which accounts for most of the error, the prediction error can be significantly reduced.

Such correction measures have the effect of making a nonlinear function closer to a linear function, so if the focus detection operation time interval is small and the movement of the image plane can be approximated to a linear function,
Especially effective. In addition, if the focus detection operation time interval is long and nonlinear elements on the image plane cannot be ignored, by making the correction coefficient close to 1, it is possible to create a prediction function that emphasizes nonlinear elements. By switching the correction coefficient according to the state in this way, it is possible to ensure high tracking performance while preventing prediction errors.

In the embodiment described above, the correction coefficient was expressed as a function of TX, which is the ratio between the focus detection operation time interval and the time lag used for prediction.

However, the correction coefficient according to the present invention is not limited to the one obtained as a function of TX, and is not limited to that obtained as a function of TX. In some cases, it is valid even if the correction coefficient is determined by other parameters, such as making the correction coefficient close to 1.Also, it is valid even if the correction coefficient is determined by other parameters (it is also valid even if it is always a constant value). It is clear that there is.

〔Effect of the invention〕

As explained above, when performing tracking correction that approximates the relationship between the image plane position and time to a multi-order function and predicts the image plane position after a time lag of a predetermined time, the prediction function correction according to the present invention is used. By doing this, prediction errors caused by focus detection errors and lens drive errors are reduced, and it becomes possible to perform highly accurate tracking corrections that are less affected by focus detection errors and lens drive errors than conventional tracking corrections. .

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing a predictive computation subroutine in an autofocus device according to the present invention, FIG. 2 is an explanatory diagram explaining the principle of driving a lens in an autofocus device using predictive computation, and FIG. An explanatory diagram explaining the error that the invention aims to solve, FIG. 4 is a circuit diagram showing an embodiment of the autofocus device of the present invention, and FIG. 5 is a program flow explaining the operation of the autofocus device shown in FIG. FIGS. 6 and 7 are explanatory diagrams showing subroutines in the program flow shown in FIG.
FIG. 8 is an explanatory diagram showing the correction coefficient calculation routine flow in the subroutine shown in FIG. 1, and FIG. 9 is an explanatory diagram for explaining lens driving using the autofocus device according to the present application. PH1・・・・・・・・・・・・・・・・・・・・・
・・・Computer LCM・・・・・・・・・・・・
・・・・・・・・・・・・Lens communication buffer circuit L
PRS ・・・・・・・・・・・・・・・・・・・・・
In-lens control circuit patent applicant Canon Co., Ltd. Image plane N quantity:) - C, 2:2 tl r: 4rsalq
Figure 6 Figure 7

Claims (1)

[Claims] A focus detection circuit that determines the amount of defocus of a photographic lens, and a lens drive circuit that drives the lens based on the output of the focus detection circuit, and an operation of detecting the amount of defocus by the focus detection circuit and a lens drive operation based on the detection result. In an automatic focus adjustment device that repeatedly performs The automatic camera is characterized by driving the lens to match the image plane position of the object and the lens after a predetermined period of time, and further comprising a correction means for correcting the highest order coefficient in the multi-order function. Focusing device.