JPH02176735A - focus adjustment device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

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 the proposal is that the relationship between the image plane position and time caused by the movement of the subject is determined in the first order by considering the detected defocus amount in each cycle, the lens drive amount, and the time interval of each cycle. It approximates functions and quadratic functions and attempts to correct the lens drive amount.
It is expected that the above problems will be improved.

However, in such a prediction method, a difference (prediction error) occurs between the predicted lens position and the actual image plane position due to the lens drive amount and focus detection error. This prediction error is magnified to several times to several times as large as the focus detection error and lens drive error. For this reason, even if the subject is within the depth of field and can be determined to be in focus using the conventional automatic focus adjustment device, if the above prediction method is used,
There was a possibility that the focus position would be outside the depth of field, resulting in an out-of-focus photo. The present applicant has proposed Japanese Patent Application No. 63-25490 as an automatic focusing method aimed at solving these problems.

The gist of the method disclosed in this proposal is to correct high-order terms that are susceptible to focus detection errors and lens drive errors and generate a large amount of prediction errors among several-order prediction functions used for prediction calculations. This is an attempt to reduce the influence of errors occurring in the lens drive system and focus detection system and improve prediction accuracy.

[Problems to be Solved by the Invention] The present invention relates to further improvements to the focus adjustment by the above-mentioned prediction method, and is intended to eliminate out-of-focus caused by correcting higher-order terms of the prediction function.

The out-of-focus caused by the above correction 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 indicates 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) represented by a broken line means the photographing lens position at time t, and when x(t) and 2(1) match, the image is in focus. [t+, t+'] indicates the focus detection operation time, and [t+', t+++] indicates the lens drive operation time. In addition, in the example shown in the same figure,
It is assumed that the image plane position changes according to a quadratic function (at2+bt+c). That is, at time t3, the current and past three image plane positions (t1+X1)(t2
+ X2 ) (t3 r Time, release time lag: The time from when the release command is issued until the start of exposure.

However, what the camera can actually detect is the image plane position
．． X2. Defocus amount DF1゜DF2 instead of X3
．． DF3 and lens drive amount DL in terms of image plane movement amount
,,DL2. The time t4 is only a future value, and in reality, it is a value that changes according to changes in the storage time of the storage type sensor due to subject brightness and changes in lens drive time due to changes in lens drive amount. For simplicity, let us assume the following.

t 4 t 3 = TL = TM 2 + (
Release time lag) (1) Based on the above assumptions, the lens drive amount D calculated from the focus detection result at time t3
L3 is found as follows.

x(t)=at2+bt+c,
(2) Then, considering (1+, 2+) in the figure as the origin, t1=OXi :DF, (3) t
2=TM, x2=DF2+DL1
(4) t3=TM, +TM2 x3=DF3+DL1+
DL2 (5) In equation (2), (3), (4),
(5) Substituting equation a.

When calculating b and c, c=DF,
(8) Therefore, the lens drive amount DL3 converted to the image plane movement amount at time t4 is: DL3=x4-1!3 =X4-X3+DF3=a ((TM, +TM2+TL)2-(TM
, +TM 2)'] 10b-TL+DF3
(9) It can be found as follows.

Next, a method of correcting the quadratic term for reducing prediction errors caused by focus detection errors and lens drive errors will be explained with reference to FIG.

FIG. 3 shows the relationship between the image plane position and time.

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 line, and the prediction error δ8 is about 11 times larger than δ1°δ2.

Therefore, the lens drive amount DL in terms of the image plane movement amount in equation (9)
3, the second-order term is corrected using the correction coefficient TF as shown in the following equation.

DL3 = TF-a((TM1+TM2+TL)2-(
TM, +TM2)"]+b-TL+DF 3(IO
) (However, O<TF≦1) In the case of Figure 3, if the correction coefficient TF=0.6, the prediction function becomes as shown by the broken line, and the prediction error δ8' is approximately 1 of the uncorrected prediction error δ8. This results in a decrease of /8.

This type of correction has the effect of bringing a nonlinear function closer to a linear function, so the focus detection operation time interval is small (if the movement of the image plane can be approximated to a linear function,
Especially effective.

However, if the movement of the image plane cannot be approximated to a linear function, out-of-focus occurs due to correction.

The occurrence of out-of-focus caused by the above correction will be explained using FIGS. 4 and 5.

In Figure 4, the vertical axis is the image plane position, and the horizontal axis is time, and shows the general change in the image plane position when the subject approaches the camera.The solid line in this figure is This is the position of the image plane that actually moves, and if it is approximated by a quadratic function, the following equation is obtained.

x (t) = at2 + bt + c (
11) On the other hand, the function corrected by the correction coefficient TF is as shown in the following equation.

X(t)=TF-a-t2+b-t+c (12)
(ago, boo, O<TF<1) Here, F+ t2 is the time when distance measurement (focus detection) was performed in the past, t3 is the current time, and t4 is the time when the predicted target is achieved. Therefore, the target for lens driving next time is X4.

However, if a correction like equation (12) is made, time t
4, the predicted image plane position is X4, and the actual value X
4, a prediction error (out of focus) of δ8 occurs. This becomes larger as the nonlinear component of the prediction function becomes larger, and becomes larger as the correction coefficient becomes smaller.

Here, in the case of an approaching subject, generally (11)
, the coefficients a and b in equation (12) are a>O,boo, and when approaching at a constant speed, a near object has a nonlinear component (in this case, a quadratic component) than a distant object. is thick (the moving speed of the image plane is also large).

That is, for a distant subject, the prediction error δ8 due to the correction of the prediction function is sufficiently small, but for a nearby subject, this error may become a problem. If the focus deviation at that time is under the general condition (a>O), there will always be a tracking delay, that is, a back-focus state.

Next, the vertical axis in FIG. 5 is the image plane position, and the horizontal axis is the time, which shows the general movement of the image plane when the subject moves away from the camera. The solid line in this figure is the position of the image plane that actually moves, and if this is approximated to a quadratic function, the following equation is obtained.

x (t)=at”+bt+c (1
3) (a>o, b<o) On the other hand, the prediction function corrected by the correction coefficient TF is as shown in the following equation.

x (t) = TF−at”+bt+c (
14) (a>0.b<o, O<TF<1) Here, 1. ．． 12 is the time when distance measurement was performed in the past,
t3 is the current time, and t4 is the prediction target time.

Therefore, the target for the next lens drive is x4.

However, if a correction like equation (14) is made, time t
4, the image plane position is predicted to be X4, and a prediction error of δ8 occurs.

Here, in the case of a subject moving away, (13), (14
) coefficients a and b are generally ago, b < O, and in the case of a subject moving away at a constant speed, the nonlinear component (here, the quadratic component) is greater for a nearby subject than for a distant subject.
is large, and the moving speed of the image plane is also large. That is, for a distant object, the prediction error due to correction of the nonlinear component of the prediction function is sufficiently small, but for a nearby object with a large nonlinear component, this error may become a problem. If this prediction error is under the general condition (a>O), the lens always tends to be in the lead, that is, in the rear focus state.

In this way, when the high-order terms of the prediction function are corrected, the tracking performance for nonlinear changes in the image plane position deteriorates, resulting in a problem that the camera is always in a back-focus state.

[Means for solving problems]

The present invention has been made in view of the above-mentioned matters, and under conditions where focus detection errors and lens drive errors become small, the correction of higher-order terms of the prediction function is loosened or eliminated, so that errors caused by the correction of the prediction function are reduced. This is to reduce the above-mentioned prediction error.

〔Example〕

FIG. 6 is a circuit diagram showing an embodiment of a camera equipped with an automatic focusing device according to the present invention.

In the figure, PH1 is a camera control device, which is, for example, a one-chip microcomputer internally having a 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 PR8 uses the synchronous communication signals 5O1SI, 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 PR8,
SI is a data signal input to the computer PRS, 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 PR8 is at a high potential level (hereinafter abbreviated as "H'), it supplies power to the lens communication buffer circuit. Serves as an inter-lens communication buffer.

Computer PR8 sets CLCM to H' and 5CLK
When predetermined data is sent from SO in synchronization with LCM
outputs buffered signals LCK and DCL of 5CLK and So to the lens via the camera-lens interface.

At the same time, a buffer signal of the signal DLC from the lens is output to SI, and PH1 inputs lens data from SI in synchronization with 5CLK.

SDR is a drive circuit for a line sensor device SNS for focus detection, which is composed of a COD or the like, and a signal CSDR.

is selected when is 'H' and is controlled from PH1 using So, SI, and 5CLK.

The signal CK is a clock for generating COD driving clocks φl and 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 AO3.

PH1 inputs AO5 from the analog input terminal, synchronizes with CK, performs A/D conversion using the internal A/D conversion function, and then outputs RA
Sequentially stored in M predetermined addresses.

Same < 5AGC, which is the output signal of SNS, is the AGC (automatic gain control: Auto Ga1n Co
This is the output of the SNS sensor, which is input to the SDR and 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 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, SI.

Controlled from PH1 using 5CLK. That is, PH1
Display member D of the camera based on the data sent from
The display of the SP is switched and the on/off state of the switch SWS linked to various operating members of the camera is notified to the PH1 by communication.

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 PR8 performs photometry and automatic focus adjustment operations when SW1 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 PR5, and even if a program is being executed when SW1 is on, an interrupt is generated by turning on SW2, and the program can immediately proceed to a predetermined interrupt program.

MTRl is a motor for film feeding, MTR2 is a motor for mirror up/down and shutter spring charging, and forward and reverse rotation are controlled by respective 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.

LPR3 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, defocus amount vs. extension amount coefficient, 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 PR5 in the camera does not need to be involved in lens driving at all until the lens driving is completed.

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.

ENCZ is an encoder circuit attached to the zoom optical system, and LPR5 receives ENCZ or a rano signal 5ENCZ to detect the zoom position. Lens parameters at each zoom position are stored in the LPR 3, and when there is a request from the PF 3 on the camera side, the 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. 7 and subsequent figures.

When a power switch (not shown) is turned on, power supply to the microcomputer PR3 is started, and PF3 starts executing the sequence program stored in the ROM.

FIG. 7 is a flowchart 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 the SWI is off, the process moves to step (003) and the R in PR8 is detected.
Clear and initialize all control flags and variables set in AM.

The above steps (002) and (003) are the switch SW1
It will run repeatedly until it is turned on or the power switch is turned off. When SWl is turned on, the process moves from step (002) to step (005).

In step (005), a "photometering" subroutine for exposure control is executed. PF3 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. 8, and the PF3 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 (OOS), a "contrast determination" subroutine is executed. The "contrast determination" subroutine evaluates the contrast of the image signal used in the focus detection calculation, and its flow is shown in FIG.

Subsequently, in step (009), a "lens driving direction determination" subroutine is executed. This subroutine determines whether the driving direction of the lens is reversed or not, and its flow is shown in FIG. 11.

In step (010), 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 (011), a "lens drive" subroutine is executed, and the lens is driven based on the lens drive amount DL corrected in the previous step (010). this"
The flow of the "lens drive" subroutine is shown in FIG. After the lens drive is completed, the process returns to step (002), and whether SW1 is turned off or switch SW2 (not shown) is turned off.
Steps (005) to (011) are repeatedly executed until the camera is turned on, and preferable focus adjustment is performed 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 (012) to start the release operation, regardless of which step it is in.

In step (013), it is determined whether lens driving is being executed, and if driving is in progress, the process moves to step (014).
A drive stop command is sent to the lens to stop the lens, and the process proceeds to step (015). If the lens is not being driven, the process immediately proceeds to step (015).

In step (015), the quick return mirror of the camera is raised. This is executed by controlling the second motor MTR2 using the motor control signals M2F and M2R shown in FIG. In the next step (016), 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 (015) and (016) have been completed is detected in step (017), but mirror-up must be confirmed with a detection switch (not shown) attached to the mirror. is possible, and the aperture control is
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 (018).

In step (018), 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 (019), a command is sent to the lens to open the aperture, and then in step (020), 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 (021), as in step (017), wait for the mirror down and aperture opening control to be completed.When both mirror down and aperture opening control are completed, step (0
22).

In step (022), the motor MT is controlled by appropriately controlling the motor control signals MIF and MIR shown in FIG.
The RI is controlled and 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. 8 will be explained.

"Image signal input" is the first operation 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), and (9).

Update 1M2. Before executing step (103), the time interval in the previous focus detection operation is stored in TM1 and 1M2, and the time at which the previous focus detection operation was started is stored in TN.

Therefore, 1M2 represents the time interval between focus detection operations from the previous time to the previous time, and TN and -TN represent the time intervals of the focus detection operation from the previous time to the current time, and this is TM in equations (6), (7), and (9).

A storage area TM1. on the RAM corresponding to 1M2. It is stored in TM2. The current time TN is stored in TN for the next focus detection operation.

That is, in step (103) the storage areas TMH, T
M2 always stores the focus detection operation time from the previous time to the previous time and from the previous time to the current time.

Now, in the next step (104), the sensor device SNS is caused to start accumulating optical images. Specifically, the microcomputer PR3 sets C3DR to H, and the sensor drive circuit SDR
In response to this, the SDR sends an "accumulation start command" as 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 PR8 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 the 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 "accumulation end command" is sent from the PH1, the SDR sets the charge transfer signal SH to 'H' for a predetermined period of time to transfer 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 AO8 amplified by sensor drive circuit SDR
Performs conversion and stores the digital signal in RAM. More specifically, the SDR uses the CCD 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 AO8 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. 9 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 "defocus amount vs. focusing lens (protrusion amount coefficient)" specific to the photographic lens,
For example, in the case of a fully projecting single lens, S=1 because the entire photographic lens is a focusing lens, and in the case of a zoom lens, S changes depending on each zoom position. "PTH" is the amount of protrusion of the focusing lens per output pulse of the encoder ENCF that is linked to the movement of the focusing lens LNS in the optical axis direction.

Therefore, the defocus amount DL to be adjusted, the above S, P
The value obtained by converting the protrusion amount of the focusing lens into the number of output pulses of the encoder using TH, the so-called lens drive amount FP
is 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). This rotates the motor LMTR and drives the 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 inputted to the circuit LPR8, and when the lens is driven, the pulse 5ENCF of the encoder circuit ENCF is counted by the counter in LPR3, and this counted value is the above-mentioned value. F
A determination as to whether the count value and FP match is made in the circuit LPR8, and the output state of the LPR8 when the count value and FP match is detected through the communication in the step (205), and the output state is detected in the step (206). ).

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) counts up a counter C0UNT that determines whether data necessary for prediction (defocus amount, lens drive amount) has been accumulated. This C0
UNT is always "0" in the initial state, and is also initialized by clearing the variable in step (303). Then, when the count-up ends, proceed to the next step. Step (303).

In (304), data for the current prediction calculation is updated.

That is, in step (303), 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 (304), 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. The data DL is the previous driving amount data, and the memory DL2 always stores the lens driving amount data performed immediately before.

In the above steps (303) and (304), the current defocus amount and lens drive amount data from a plurality of times in the past are updated and stored in each memory.

In the next step (305), it is determined whether CI=O, which is calculated by a "contrast determination" subroutine to be described later. If CI=O, the contrast of the image signal is very low (low contrast) and the focus detection accuracy is poor, so the process goes to step (306).
In step 6), the counter is initialized to re-accumulate the data necessary for prediction. This can prevent prediction calculations with poor prediction accuracy based on extremely unreliable data.

If CI=O is not determined in step (305), that is, the contrast of the image signal is at least a certain level, and the focus detection accuracy is at least a predetermined level, step (307
).

In step (307), the previous counter C0UNT is 2.
It is determined whether or not it is greater than or equal to 2, and if it is less than or equal to 2, step (308
), otherwise the process proceeds to step (309), and if step (306) is completed, the process also proceeds to step (308). This step (308) is to calculate the lens drive amount when prediction is not performed, and the lens drive amount DL is the currently detected defocus amount DEF. When step (308) is completed, the process returns to step (314).

At step (307), counter COUNT is "2"
If it is larger, it is determined that it is predictable and step (309
).

In steps (309) and (310), each memory D
F1-DF3. DL1. DL2. Based on the data stored in TMl and TM2, A and B representing terms a and b in equations (6) and (7) are determined.

In step (311), an expected 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 (constant).

As mentioned above, the memory area TM2 stores the focus detection operation time from the previous time to the current time, and the time lag is calculated based on the assumption that the current focus detection operation time is the same as the previous focus detection operation time. Find TL=TM2+TR.

In the next step (312), a correction coefficient TF is determined in a subroutine to be described later, and the process moves to step (313).

In this step (313), the following formula (formula (10) described above) is calculated based on the data in each memory and the calculated values in steps (309) to (312), and DL = TF-A [(TM , +7M2+TL)"-
(TM 1+TM2)')+B-TL+DF 3
(15) Calculate the lens drive amount DL in terms of the current image plane movement amount.

After this, the process returns to step (314).

In this way, when the prediction calculation is performed, step (01
In step 1), 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 “contrast judgment” subroutine is
This will be explained using Figure 0. FIG. 10 shows the flow of the "contrast determination" subroutine, which determines the contrast of the image signal, that is, the reliability of the focus detection result.

In step (402), the contrast CNT is determined from the digital value corresponding to the image pattern of the photoelectric conversion element obtained in the image signal input subroutine described above. This contrast C
NT detection is well known, and detailed explanation thereof will be omitted.

In the next step (403), it is compared whether the previously determined contrast CNT is larger than a predetermined value CA.

If CNT>CA, proceed to step (404); otherwise, proceed to step (405). In step (404), it is determined that the contrast is very high and the accuracy of focus detection is high, and the reliability of focus detection is evaluated.
Let I=2. After completing step (404), the process returns to step (408).

Further, when the process proceeds from step (403) to step (405), the contrast CNT is again compared with a predetermined value CB, and if CNT>CB, the process proceeds to step (406); otherwise, the process proceeds to step (407). Step (40
In 6), it is determined that the focus detection result has a certain degree of reliability, and CI=1 is set to evaluate the reliability of focus detection. In step (407), the contrast is very low (
It is determined that the reliability of the focus detection result is low, and CI for evaluating reliability is set to 0.

After completing step (406) or (407), the process returns to step (408).

Here, CA>CB, and the value of CB is the lower limit of reliability that can withstand prediction calculations.

In this embodiment, reliability is evaluated in three stages, but it is not necessary to evaluate the reliability in three stages, and evaluation may be performed in multiple stages or in no stage.

Next, the flow of the "lens drive direction determination" subroutine will be explained with reference to FIG. FIG. 11 shows the flow of "Lens Drive Direction Determination", in which it is determined whether the lens drive direction has been reversed between the previous time and the current time.

In step (502), the previous lens drive amount DL.

IDL and -DL2 are calculated from the current lens drive amount DL2, and this value is compared with the magnitude of 1DL2+. Here, if the current and previous lens drives are in the same direction, DL,
The signs of DL and DL2 are the same, and the following equation is obtained.On the other hand, if the current and previous lens drive directions are reversed, the signs of DL and DL2 are opposite, and the following equation is obtained.

DL, -DL2 > l DL2 That is, if the driving direction of the lens is not reversed, the process proceeds to step (504), and if it is reversed, the process proceeds to step (50).
Move on to 3).

In step (504), LI=1 indicating that the lens drive direction is the same, in step (503) LI=O indicating that the lens drive direction has been reversed, and in step (50
5) returns this subroutine.

In this subroutine, when the lens drive direction is reversed,
We believe that lens drive accuracy decreases due to backlash in the lens drive system, and that lens drive accuracy is otherwise high. That is, LI is a parameter for evaluating lens drive accuracy.

Here, in this example, LI, which is a parameter of lens driving accuracy, was evaluated in two stages depending on the driving direction of the lens.
It may be evaluated in conjunction with other parameters.

Next, the flow of the “correction coefficient calculation” subroutine is
This will be explained with a diagram. FIG. 12 shows the flow of the "correction coefficient calculation" subroutine. In step (602), from the focus detection accuracy evaluation parameter CI and the lens drive accuracy evaluation parameter LI, when CI+LI=3, the process proceeds to step (603). If not, step (60
Move on to 4).

Here, the condition for CI+LT=3 is CI=2. L
I=1, which indicates that focus detection accuracy and lens drive accuracy are high, that is, prediction errors due to focus detection errors and lens drive errors are small.

In step (603), it is determined that there is no need for correction, and T
Set F=1 and return at step (606).

In step (604), it is determined that the focus detection accuracy and lens drive accuracy are not high enough to eliminate the correction, and the ratio of the focus detection operation time interval to the time lag used for prediction TX = (T
M, +TM2)/(2・TL) for each storage area TM3
, 7M2 and the TL obtained in step (311) above, and proceed to the next step.

In step (605), a coefficient TF for correcting the quadratic term is calculated using the TX obtained in step (604),
Return.

In this embodiment, if the release time lag is constant, T
Focusing on the fact that the focus detection operation time interval is short when the value of
If the
I set it like this.

With the above configuration, CI=2. When LI=1 is determined, TF=1 by calculating the correction coefficient in FIG.
is set. Therefore, prediction calculations are performed without correcting the prediction function.

Moreover, the above CI=2. When LI=1, the prediction function will be corrected.

Therefore, when the prediction error due to focus detection error or lens driving error is small, predictive calculation is performed without correcting the prediction function to prevent the error caused by the above correction, while when the prediction error is large, the above correction is performed to reduce the prediction error. I'm trying to keep it small.

In the above embodiment, the focus detection accuracy was evaluated based only on the contrast of the image signal, but other parameters such as an increase in the storage time of the photoelectric conversion element or an increase in the temperature of the element may also be considered. If this happens, the noise component in the image signal will be magnified and the focus detection accuracy will deteriorate. In this way, focus detection accuracy can be evaluated based on accumulation time, temperature, and humidity.Furthermore, focus detection accuracy is also degraded by optical ghosts, etc., so focus detection accuracy can be evaluated based on backlight detection means and the similarity of the two images. may be evaluated.

The lens drive accuracy varies depending on the actuator and drive system configuration, so the lens ID
and other parameters, open F&.

It may be evaluated based on the lens configuration.

Then, if it is determined that the prediction is inappropriate based on the parameters, it is possible to prohibit the prediction, and under conditions where correction is necessary, it is possible to make a judgment such as adding correction.

In addition, in the above example, only the accuracy of backlash at DL2 and contrast at DF3 was evaluated;
DFl, DF2. DF3. The accuracy of each of DL, DL2 may be considered to determine the presence or absence of correction, its strength, and whether prediction is possible or not.

Additionally, if the lens driving direction is continuously reversed, the subject may not require prediction or may be inappropriate, so predictive AF should be prohibited in such cases. is also possible.

In the present invention, the focus detection accuracy and lens drive accuracy are evaluated in predictive AF, and based on this, it is determined whether or not the predictive function can be corrected.

It is also possible to determine invincibility and prohibit predictive AF if necessary.

〔Effect of the invention〕

As explained above, conventional lens drive errors.

In order to prevent prediction errors due to focus detection errors, higher-order terms in the prediction function are corrected, which degrades tracking performance for nonlinear movements of the image plane. However, according to the present invention, lens drive accuracy and focus By stopping the correction when it is determined that the detection accuracy is high, that is, when it is determined that the prediction error is small, there is an effect that the tracking performance for nonlinear movements under such conditions can be improved.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing a program for explaining predictive calculation operations in the focus adjustment device of the present invention. FIG. 2 is a diagram illustrating the principle of driving the lens of the focus adjustment device of the present invention. FIG. 3 is an explanatory diagram of prediction errors caused by focus detection errors and lens drive errors. FIGS. 4 and 5 are explanatory diagrams of occurrence of prediction errors due to correction of prediction functions. FIG. 6 is a circuit diagram showing an embodiment of the focus adjustment device of the present invention. FIG. 7 is an explanatory diagram showing a program flow for explaining the overall operation of the automatic focus adjustment device shown in FIG. FIG. 8 is an explanatory diagram showing the "image signal input" subroutine in FIG. 7. FIG. 9 is an explanatory diagram showing the "lens drive" subroutine in FIG. 7. FIG. 10 is an explanatory diagram showing the "contrast determination" subroutine in FIG. 7. FIG. 11 is an explanatory diagram showing the "lens drive direction determination" subroutine in FIG. 7. FIG. 12 is an explanatory diagram showing the "correction coefficient calculation" subroutine in FIG. 1. PH1...Microcomputer LCM...Buffer circuit SNS...Sensor device (θ6υ (dol)

Claims (4)

[Claims] (1) In a focus adjustment device that drives a lens based on the output of a focus detection circuit, the amount of lens drive or the image plane of the subject is determined based on focus adjustment data from multiple past focus adjustment operations, depending on the position of the subject after a predetermined period of time. A calculation circuit that calculates the position based on a predetermined function is provided, and the lens is driven to focus on the subject position after a predetermined time, and the function is corrected and the above calculation is performed using the correction function. A focus adjustment device comprising: a correction circuit; and a determination circuit that determines whether or not the correction circuit is activated in accordance with the focus adjustment data in the focus adjustment operation. (2) The focus adjustment device according to claim 1, wherein the determination circuit determines the accuracy of the focus adjustment data, operates a correction circuit when the accuracy is low, and disables the correction circuit when the accuracy is high. . (3) The focusing device according to claim 2, wherein the function is a several-order function, and the correction circuit reduces coefficients of higher-order terms of the function. (4) In a focus adjustment device that drives a lens based on the focus detection circuit output, the amount of lens drive or the image plane of the subject is determined based on focus adjustment data from multiple past focus adjustment operations, depending on the position of the subject after a predetermined period of time. A calculation circuit that calculates the position based on a predetermined function is provided, the lens is driven to focus on the subject position after a predetermined time, and the calculation is performed using a second function different from the predetermined function. A focus adjustment device comprising: an arithmetic control circuit for performing the focus adjustment operation; and a determination circuit for determining whether to operate or deactivate the arithmetic control circuit in accordance with the focus adjustment data in the focus adjustment operation.