JPH0541967B2 - - Google Patents

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]

Traditionally, most automatic focus adjustment systems for single-lens reflex cameras attempt to focus on the subject by repeating the cycle of focus detection (sensor signal input, focus detection calculation) and lens drive. be. 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 the lens drive ends.

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

However, in the case of a subject with large movements, the amount of def focus changes during focus detection and lens drive, and the amount of def focus to be eliminated and the amount of detected def focus may be significantly different. The problem is that the image is out of focus.

The present applicant has proposed Japanese Patent Application No. 62-263728 as an automatic focusing method aimed at solving the above problems.

The gist of the method disclosed by the proposal is as follows:
Considering the amount of detected defocus in each cycle, the amount of lens drive, and the time interval of each cycle, the relationship between the image plane position and time due to the movement of the subject is calculated as follows.
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.

However, in such a prediction method, a difference (prediction error) occurs between the predicted lens position and the actual image plane position due to lens drive errors and focus detection errors. This prediction error is magnified to several times to ten 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 with conventional automatic focus adjustment devices, if the above prediction method is used, the focus position will be outside the depth of field and the subject will be out of focus. There was a possibility that it would turn into a photograph. 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 the proposal is that, among the multi-order prediction functions used in prediction calculations, the high-order terms are susceptible to focus detection errors and lens drive errors, and generate a large amount of prediction errors. By correcting this, the effect of errors occurring in the lens drive system and focus detection system is reduced, and the prediction accuracy is improved.

[Problem that the invention is trying to solve]

The present invention relates to further improvements in focus adjustment using the above prediction method, and is intended to eliminate out-of-focus caused by correcting higher-order terms of the prediction function.

The focus shift 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. l(t) indicated by a broken line means the position of the photographing lens at time t, and when x(t) and l(t) match, the image is in focus. [t _i , t _i ] represents the focus detection operation time, and [t _i ′, t _i+1 ] represents 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 (at ² +bt+c). That is, at time t ₃ , the current and past three image plane positions (t ₁ , x ₁ )
If (t ₂ , x ₂ ) (t ₃ , x ₃ ) is known, TL from time t ₃
Time after (AF time lag + release time lag)
The image plane position x ₄ at t ₄ can be predicted (AF
Time lag: Time required for focus detection and lens drive, Release time lag: Time from when a release command is issued until exposure starts.

However, what the camera actually detects is not the image plane positions X ₁ , X ₂ , and X ₃ but the differential focus amounts DF ₁ ,
These are DF ₂ and DF ₃ as well as lens drive amounts DL ₁ and DL ₂ in terms of image plane movement amount. Time _t4 is just a value in the future, and is actually a value that changes as the storage time of the storage type sensor changes due to subject brightness and the lens drive time changes due to changes in the amount of lens drive. However, for simplicity, we assume the following.

t ₄ − t ₃ = TL = TM ₂ + (release time lag)
(1) Under the above assumptions, the lens drive amount DL ₃ calculated from the focus detection result at time t ₃ is determined as follows.

x(t)=at ² +bt+c (2) And considering the origin of (t ₁ , l ₁ ) in the figure, t ₁ = 0 x ₁ = DF ₁ (3) t ₂ = TM ₁ x ₂ = DF ₂ +DL ₁ (4) t ₃ = TM ₁ + TM ₂ x ₃ = DF ₃ + DL ₁ + DL ₂ (5) Substituting equations (3), (4), and (5) into equation (2), a, b, When calculating c, a=DF ₃ +DL ₂ −DF ₂ /(TM ₁ +TM ₂ )・TM ₂ + DF ₁ −DL ₁ −DF ₂ /(TM ₁ +TM ₂ )・TM ₁ (6) b=DF ₂ +DL ₁ -DF ₁ -a・TM ₁ ² /TM ₁ (7) c=DF ₁ (8) Therefore, the lens drive amount DL ₃ converted to the image plane movement amount at time t ₄ is DL ₃ = x ₄ - l ₃ = x ₄ − x ₃ + DF ₃ = a {(TM ₁ + TM ₂ + TL) ² − (TM ₁ +
TM ₂ ) ² } +b・TL+DF ₃ (9)

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

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

Assuming that the solid line in this figure is the image plane position that actually moves due to the movement of the subject, if an error of δ ₁ and δ ₂ occurs at t ₁ and t ₂ , respectively, the prediction function will change to the dot-dashed line. The prediction error δ _e is approximately 11 of δ ₁ and δ ₂
It has become twice the size.

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

DL ₃ = TF・a {(TM ₁ + TM ₂ + TL) ² − (TM ₁ +
TM ₂ ) ² } +b・TL+DF ₃ (10) (0<TF≦1) In the case of Fig. 3, if the correction coefficient TF=0.6, the prediction function will be as shown by the broken line, and the prediction error δ _e ′ will be reduced to about 1/8 of the uncorrected prediction error δ _e .

Such correction measures have the effect of bringing a nonlinear function closer to a linear function, so it is particularly effective when the focus detection operation time interval is short and the movement of the image plane can be approximated to a linear function.

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.
This shows a general change in the image plane position when a subject approaches 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 ² +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・t ² +b・t+c (12) (a>0, b>0, 0<TF<1) Here, t ₁ and t ₂ are distance measurement (focus detection) performed in the past. _t3 is the current time, and _t4 is the predicted target time. Therefore, the target for the next lens drive is _x4 .

However, if a correction like equation (12) is made, the time
The predicted image plane position at t ₄ is x ₄ ′, which is the actual value
A prediction error (out of focus) of δ _e occurs for x ₄ . 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
The coefficients a and b of equations (11) and (12) are a>0, b>0,
When approaching at a constant speed, a nearby object has a nonlinear component (here 2
(next component) is large, and the moving speed of the image plane is also large. That is, for a distant subject, the prediction error δ _e due to 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>0), the tracking will always be delayed, that is, the object will be in a backward 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 ² +bt+c(13) (a>0, b<0) On the other hand, the prediction function corrected by the correction coefficient TF is as shown in the following equation.

x(t)=TF・at ² +bt+c(14) (a>0, b<0, 0<TF<1) Here, t ₁ and t ₂ are times when distance measurement was performed in the past, and t ₃ is the current time, and _t4 is the prediction target time. Therefore, the goal for the next lens drive is x ₄
It is.

However, if a correction like equation (14) is made, the time
The image plane position at t ₄ is predicted to be x ₄ ′, and a prediction error of δ _e occurs.

Here, in the case of a subject moving away, the coefficients a and b in equations (13) and (14) are generally a > 0, b < 0, and in the case of a subject moving away at a constant speed, a nearby subject is more important than a distant subject. The nonlinear component (here, the second-order component) is larger, and the moving speed of the image plane is also larger. 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>0), 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 includes a focus adjustment device that drives a lens based on the output of a focus detection circuit. An arithmetic circuit is provided that predicts and calculates the amount of lens drive corresponding to the image plane position of the object or the amount of lens drive that corresponds to the image plane position of the object using a high-order functional formula, and drives the lens to bring the object into focus after a predetermined period of time. , a correction circuit that performs the predictive calculation using a correction function formula having a correction coefficient obtained by multiplying the highest order coefficient of the function formula by a predetermined value smaller than 1 and larger than 0; When the reliability of the data is low, the correction circuit performs a predictive calculation using a correction function formula, and when the data reliability is high, the prediction calculation is performed using a function formula before correction. A circuit is provided to solve the above problem.

〔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, PRS is a camera control device, for example, it contains a CPU (central processing unit), ROM, RAM, etc.
It is a 1-chip microcomputer with A/D conversion function. The computer PRS performs a series of camera operations such as automatic exposure control function, automatic focus detection function, and film winding according to the camera sequence program stored in the ROM.
For this purpose, the computer PRS uses synchronous communication signals SO, SI, SCLK, communication selection signals CLCM,
CSDR and CDDR are used to communicate with peripheral circuits and lenses within the camera body and control the operation of each circuit and lens.

SO is a data signal output from computer PRS, SI is a data signal input to computer PRS, and SCLK 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 connects the camera when the selection signal CLCM from the computer PRS is at a high potential level (hereinafter abbreviated as 'H'). This creates a communication buffer between lenses.

Computer PRS sets CLCM to 'H',
When predetermined data is sent from the SO in synchronization with SCLK, the LCM transmits the data via the camera-lens interface.
Outputs SCLK and SO buffer signals LCK and DCL to the lens. At the same time, the buffer signal of the DLC signal from the lens is output to the SI, and the PRS is
Input lens data from SI in synchronization with SCLK.

SDR is a drive circuit for the line sensor device SNS for focus detection, which is composed of CCD, etc.
Selected when CSDR is 'H', SO, SI,
Controlled from PRS using SCLK.

The signal CK is a clock for generating CCD driving clocks φ1 and φ2, and the signal INTEND is a signal to notify the PRS that the accumulation operation has ended.

The output signal OS of the SNS is a time-series image signal synchronized with the clocks φ1 and φ2, and after being amplified by the amplifier circuit in the SDR, it is output to the PRS as the AOS.
PRS inputs AOS from the analog input terminal, and CK
In synchronization with , the data is A/D converted by an internal A/D conversion function, and then sequentially stored at a predetermined address in the RAM.

SAGC, which is also the output signal of SNS, is
AGC (Auto Gain Control)
It is the output of the sensor for
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
SSPC is input to the analog input terminal of PRS,
After A/D conversion, it is used for automatic exposure control AE according to a predetermined program.

DDR is a switch detection and display circuit,
Selected when signal CDDR is 'H', SO, SI,
Controlled from PRS using SCLK. That is, PRS
It switches the display of the camera's display member DSP based on the data sent from the camera, and notifies the PRS via communication of the on/off status of the switch SWS that is linked to the camera's various operating members.

Switches SW1 and SW2 are switches linked to a release button (not shown); SW1 is turned on when the release button is pressed to the first stage, and SW2 is turned on when the release button is pressed to the second stage. As will be described later, the computer PRS performs photometry and automatic focus adjustment when SW1 is turned on, and performs exposure control and film winding using SW2 as a trigger.
Note that SW2 is connected to the "interrupt input terminal" of the microcomputer PRS, and even if a program is being executed when SW1 is on, an interrupt is generated when SW2 is on, and the program can immediately proceed to a predetermined interrupt program.

MTR1 is a motor for film feeding, MTR2 is a motor for mirror up/down and shutter spring charging, and each drive circuit MDR1, MDR
2 controls forward and reverse rotation. Signal M1 input from PRS to MDR1 and MDR2
F, M1R, M2F, and M2R are signals for motor control.

MG1 and MG2 are magnets for starting the shutter front and rear curtains, respectively, and are energized by signals SMG1 and SMG2 and amplification transistors TR1 and TR2, and the PRS
Shutter control is performed by

Note that the switch detection and display circuit DDR, motor drive circuits MDR1 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 LPRS 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.

LPRS analyzes the command according to a predetermined procedure and performs focus adjustment, aperture control, and output DLC.
Various parameters of the lens (open F-number, focal length, coefficient of defocus amount vs. extension amount, etc.) are output.

In the example, an example of a zoom lens is shown,
When a focus adjustment command is sent from the camera,
According to the drive amount and direction sent at the same time, the focus adjustment motor LMTR is driven by signals LMF and LMP to move the optical system in the optical axis direction and perform focus adjustment. The amount of movement of the optical system is determined by the encoder circuit ENCF.
The pulse signal SENCF is used to monitor the pulse signal SENCF, and the counter in the LPRS is used to count the signals.When the specified movement is completed, the LPRS itself sets the signals LMF and LMR to 'L'.
to brake the motor LMTR.

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

Also, when an aperture control command is sent from the camera, a stepping motor, which is known for driving the aperture, is activated according to the number of aperture stages sent at the same time.
Drives DMTR.

ENCZ is an encoder circuit attached to the zoom optical system, and LPRS inputs the signal SENCZ from ENCZ to detect the zoom position. Lens parameters at each zoom position are stored in the LPRS, and when a request is made from the PRS 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 flowchart shown in FIG. 7 and subsequent figures.

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

FIG. 7 is a flowchart showing the overall flow of the above program. When the program starts running with the above operation, it will pass through step (001).
At step (002), press the first release button.
The state of switch SW1, which is turned on by pressing the step, is detected, and when SW1 is off, the process moves to step (003), where all control flags and variables set in the RAM in the PRS are cleared and initialized. do.

The above steps (002) and (003) are switch SW1
is executed repeatedly until it is turned on or the power switch is turned off. Step (002) to step (005) when SW1 turns on.
Move to.

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

Next, in step (006), an "image signal input" subroutine is executed. The flow of this subroutine is shown in FIG. 8, and the PRS 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. A detailed calculation method has been disclosed by the applicant in Japanese Patent Application No. 160824/1982, and a detailed explanation thereof will be omitted.

In step (008), 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.

Next, in step (011), "lens drive"
The subroutine is executed and the lens is driven based on the lens drive amount DL corrected in the previous step (010). The flow of this "lens drive" subroutine is shown in FIG. After the lens drive is completed, the process returns to step (002), and steps (005) to (011) are repeated until SW1 is turned off or switch SW2 (not shown) is turned on. Good focusing is achieved even when

Now, when the release button is pressed further and the switch SW2 is turned on, the interrupt function immediately moves to step (012) to start the release operation, regardless of the step.

In step (013), it is determined whether the lens is being driven. If it is, step (014) is executed.
, send a driving stop command to the lens, stop the lens, and proceed to step (015). If the lens is not being driven, immediately proceed to step (015).
Proceed to.

In step (015), the camera's quick return mirror 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 (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), and mirror up can be confirmed with a detection switch (not shown) attached to the mirror. For aperture control, it is confirmed through communication whether the lens has been driven to a predetermined aperture value. If any of them is not completed, the process waits at this step and continues to detect the status. When it is confirmed that both control ends, 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 shutter control is completed, the next step (019) is to send a command to the lens to open the aperture, and then step (020)
Perform a mirror down. 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), the process waits for mirror down and aperture opening control to be completed. When both mirror down and aperture opening control are completed, the process moves to step (022).

In step (022), the motor MTR1 is controlled by appropriately controlling the motor control signals M1F and M1R shown in FIG. 6, 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 to be executed in a new focus detection operation, and when this subroutine is called, the microcomputer PRS itself will perform step (101) and step (102). The timer value TIMER of the self-running timer
By storing it in the storage area TN on RAM,
The start time of the focus detection operation is stored.

In the next step (103), TM ₁ , which corresponds to the time interval in lens drive amount correction equations (6), (7), and (9)
Update TM ₂ . Before step (103) is executed, TM ₁ and TM ₂ have stored the time interval of the previous focus detection operation, and TN ₁ has stored the time when the previous focus detection operation was started. There is.

Therefore, TM ₂ is TN ₁ −TN from the previous time to the previous time.
represents the time interval of the focus detection operation from the previous time to the current time, and this is stored in the storage areas TM ₁ and TM ₂ on the RAM corresponding to TM ₁ and TM ₂ in equations (6), (7), and (9). That is why it is done. The current time TN is stored in TN ₁ 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 TM ₁ and TM ₂ .

Now, in the next step (104), the sensor device SNS
starts accumulating a light image. Specifically, the microcomputer PRS sets CSDR to H, communicates with the sensor drive circuit SDR, and sends an "accumulation start command" as SO, and in response, the SDR activates the photoelectric conversion element section of the sensor device SNS. Clear signal CLR
Set to 'L' to start charge accumulation.

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

In the next step (106), the state of the INTEND terminal input to the computer PRS is detected, and it is checked whether or not accumulation has ended. The sensor drive circuit SDR sets the signal INTEND to 'L' at the same time as the accumulation starts, monitors the AGC signal SAGC (signal representing the accumulated amount) from the sensor device SNS, and when the SAGC reaches a predetermined level, sets the signal INTEND to 'H'. ', and at the same time, the charge transfer signal SH is set to 'H' for a predetermined period of time to transfer the charges in the photoelectric conversion element section to the CCD section.

If the INTEND terminal is 'H' at step (106), it means that the accumulation has finished, and the process returns 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 of the free-running timer is
From TIMER, the time memorized in step (105)
Subtract TI and store it in variable TE. Therefore, the time from the start of accumulation to this point, the so-called accumulation time, is stored in TE. The next step (108) compares TE with the constant MAXINT, and if TE is
If it is less than MAXINT, return to step (106),
Waiting for the accumulation to finish again. When TE exceeds MAXINT, the process moves to step (109) and the accumulation is forcibly terminated. Forced storage termination is done by computer.
This is executed by sending an "accumulation end command" from PRS to circuit SDR using the above communication signal. SDR
When the "accumulation end command" is sent from PRS,
The charge transfer signal SH is set to 'H' for a predetermined period of time to transfer the charges in the photoelectric conversion section to the CCD section. The sensor accumulation ends with the flow up to step (109).

In step (110), the image signal of the sensor device SNS is
The sensor drive circuit SDR amplifies the OS and performs A/D conversion of the signal AOS and stores the digital signal in the RAM. To explain in more detail, SDR is
The CCD driving clocks φ1 and φ2 are generated in synchronization with the clock CK from PRS and applied to the control circuit inside the SNS. is output from the output OS in chronological order. After this signal is amplified by the amplifier inside the SDR, it is input as AOS to the analog input terminal of the PRS. PRS performs A/D conversion in synchronization with the clock CK that it outputs, and sequentially converts the digital image signal after A/D conversion.
It is stored at a specified address in RAM.

When the image signal input is completed in this way, the "image signal input" subroutine is returned at step (111).

FIG. 9 shows a flowchart of the "lens drive" subroutine.

When this subroutine is executed, in step (202) it communicates with the lens and inputs two data "S" and "PTH". "S" is the "coefficient of the amount of defocus vs. the amount of protrusion of the focusing lens" that is specific to the taking lens. For example, in the case of a single lens that extends entirely, S = 1 because the entire taking lens is the focusing lens. , 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 linked to the movement of the focusing lens LNS in the optical axis direction.

Therefore, the defocus amount DL to be adjusted, the value obtained by converting the protrusion amount of the focusing lens into the number of output pulses of the encoder using the above S and PTH, the so-called lens drive amount FP, is given by the following equation.

FP=DL×S/PTH Step (203) executes the above equation as is.

In step (204), the value obtained in step (203) is
Sends the FP to the lens and commands the driving of the focusing lens (or the entire photographing lens in the case of a fully extended single lens). This rotates the motor LMTR and drives the lens.

In the next step (205), the lens communicates with the lens and detects whether or not the lens drive amount FP commanded in step (206) has been completed.When the drive is completed, the process moves to step (206) and "lens "Drive" subroutine returns.

In addition, the end of lens drive is detected by the amount of drive as described above.
When FP is input to the circuit LPRS and the lens is driven, the encoder circuit ENCF pulses.
SENCF is counted by a counter in LPRS, and it is determined whether this counted value matches the above FP or not in the circuit LPRS, and the output state of LPRS when the counted value and FP match. is detected in the communication at the above step (205) and the above step (206)
This is a transition to

Next, the flow of the “prediction calculation” subroutine is
This will be explained with a diagram. FIG. 1 shows the flow of the "prediction calculation" subroutine, which calculates the lens drive amount taking into account the release time lag.

In step (302), a counter COUNT is counted up to determine whether data necessary for prediction (defocus amount, lens drive amount) has been accumulated. This COUNT is always “0” in the initial state
It is also initialized by clearing the variable in step (303). Then, when the count-up ends, proceed to the next step. In steps (303) and (304), data for the current prediction calculation is updated.

That is, in step (303), data in memory _DF2 is input to _DF1 . Before the current subroutine is executed, the previous defocus amount has been input to the memory DF ₂ , but at the time the current subroutine is executed, the contents of DF ₂ become the previous previous defocus amount. Therefore, this is input into memory DF ₁ so that the previous def focus amount is always stored in memory DF ₁ .

Also, input the contents of memory DF ₃ to DF ₂ , _and
The previous def focus amount and the current detected def focus amount DEF are always stored in the DF ₃ so that the current def focus amount is always stored in the DF ₃ .

Also, in step (304), the data in the memory DL ₂ is input to the memory DL ₁ , and the lens drive data from the previous time is always stored in DL ₁ . Also input data DL to memory DL ₂ . The data DL is the previous driving amount data, and the memory DL ₂ always stores the lens driving amount data performed immediately before.

In the above steps (303) and (304), the current def focus amount and lens drive amount data from the past multiple times are updated and stored in each memory.

In the next step (305), it is determined whether CI=0, which is calculated by a "contrast determination" subroutine to be described later. If CI = 0, the contrast of the image signal is very low (low contrast) and the focus detection accuracy is poor, so proceed to step (306). In step (306), the counter is initialized and the data necessary for prediction is collected. Enable re-accumulation. This makes it possible to prevent prediction calculations with poor prediction accuracy based on extremely unreliable data.

CI=0 at step (305), i.e.
The contrast of the image signal is above a certain level,
If the focus detection accuracy is above the predetermined level, the process advances to step (307).

At step (307), the previous counter COUNT
Determine whether or not is 2 or more, and if it is 2 or less, proceed to step (308), otherwise proceed to step (309). (308). This step (308) is to calculate the lens drive amount when no prediction is performed, and the lens drive amount DL is the currently detected defocus amount.
It is DEF. When step (308) is completed, the process returns to step (314).

If the counter COUNT is greater than "2" in step (307), it is determined that prediction is possible and the process proceeds to step (309).

In steps (309) and (310), each memory DF ₁
〜A representing terms a and b in equations (6) and (7) based on the data stored in DF ₃ , DL ₁ , DL ₂ , TM ₁ , TM ₂ ,
Find B.

In step (311), the expected time lag TL is calculated. This calculation is executed by calculating the sum of the data in the storage area TM ₂ and the release time lag TR (constant). As mentioned above, the memory area TM ₂ stores the focus detection operation time from the previous time to the current time, and on the assumption that the current focus detection operation time is the same as the previous focus detection operation time. Find time lag TL=TM ₂ +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) above) is calculated based on the data in each memory and the calculated values in steps (309) to (312), and DL=TF・A[(TM ₁ +TM ₂ +TL) ² -(TM ₁ +
TM ₂ ) ² ] +B・TL+DF ₃ (15) Find the lens drive amount DL in terms of the current image plane movement amount. After this, the process returns to step (341).

After the predictive calculation is performed in this manner, the lens is driven as described above in step (011), and the lens is moved to a position where the image plane positions match.

Next, the flow of the "contrast determination" subroutine will be explained with reference to FIG. 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 CNT 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)
Move to. In step (404), it is determined that the contrast is very high and the accuracy of focus detection is high, and CI=2 is set to evaluate the reliability of focus detection. After completing step (404), the process returns to step (408).

Further, when proceeding 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). In step (406), 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),
It is determined that the contrast is very low and the reliability of the focus detection result is low, and the reliability is evaluated as CI=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. Figure 11 shows the flow of "lens drive direction determination".
This is to determine whether the driving direction of the lens has been reversed between the previous time and the current time.

In step (502), the previous lens drive amount is
From DL ₁ and current lens drive amount DL ₂ | DL ₁ −DL ₂
| is calculated, and this value is compared with the magnitude of |DL ₂ |. Here, if the current and previous lens drives are in the same direction, the signs of DL ₁ and DL ₂ are the same, and the following equation is obtained.

|DL ₁ −DL ₂ |<|DL ₂ | On the other hand, if the current and previous lens driving directions are opposite, the signs of DL ₁ and DL ₂ are opposite, and the following equation is obtained.

|DL ₁ −DL ₂ |>|DL ₂ | 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 (503).

In step (504), LI = 1 indicating that the lens driving direction is the same, and in step (503) LI = 0 indicating that the lens driving direction has been reversed.
This subroutine is returned at step (505).

This subroutine assumes that when the lens driving direction is reversed, the lens driving accuracy is reduced due to backlash in the lens driving system, and that otherwise the lens driving accuracy is high. That is, LI
is a parameter for evaluating lens drive accuracy.

Here, in this example, LI, which is a parameter of lens drive accuracy, was evaluated in two stages depending on the lens drive direction, but the quality of drive accuracy was also evaluated in conjunction with parameters such as lens ID and aperture f/number. You may do so.

Next, the flow of the "correction coefficient calculation" subroutine will be explained with reference to FIG. Figure 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 moves to step (603); otherwise, the process moves to step (604).

Here, the conditions for CI+LI=3 are CI=2,
LI=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, TF=1, and the process returns in 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.
The ratio TX = (TM ₁ + TM ₂ )/(2・TL) between the focus detection operation time interval and the time lag used for prediction is calculated using the data of each storage area TM ₁ and TM ₂ and the TL obtained in step (311) above. Calculate based on this 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), and the process returns.

In this example, we focused on the fact that if the release time lag is constant, the focus detection operation time interval becomes shorter when the value of TX is small, and the correction coefficient TF is set to become smaller as TX becomes smaller (0 <TF≦1). Also, if TX is large, TF
Making it too small will have a negative effect, so
When TX is large, TF is set to approach 1.

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

Further, when CI=2 and LI=1, the prediction function is corrected.

Therefore, when the prediction error due to focus detection error or lens drive error is small, predictive calculation is performed without correcting the prediction function to prevent the error caused by the above correction.On the other hand, when the prediction error is large, the above correction is performed to reduce the prediction error. is made to be 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 the longer storage time of the photoelectric conversion element or the higher temperature of the element 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, and since focus detection accuracy is also reduced by optical ghosts, it is important to evaluate the backlight detection method and the similarity of the two images. Focus detection accuracy may be evaluated by

Regarding lens drive accuracy, since drive accuracy varies depending on the actuator and drive system configuration, lens ID and other parameters, aperture f/number,
Evaluation may also be made 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 the backlash at DL ₂ and the contrast at DF ₃ was evaluated, but the accuracy of each of DF ₁ , DF ₂ , DF ₃ , DL ₁ , and DL ₂ was taken into account and the correction was performed. The presence or absence, strength, or even predictability may be determined.

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, focus detection accuracy and lens drive accuracy are evaluated in predictive AF, and based on this, it is determined whether the predictive function can be corrected.
It is also possible to determine whether the target is suitable or unbeatable, and prohibit predictive AF if necessary.

〔Effect of the invention〕

As explained above, conventionally, in order to prevent prediction errors due to lens drive errors and focus detection errors, high-order terms of the prediction function are corrected, and this improves tracking performance for nonlinear movements of the image plane. However, according to the present invention, when it can be determined that the lens drive accuracy and focus detection accuracy are high, that is, when it can be determined that the prediction error is small, the correction is stopped, thereby reducing nonlinearity under such conditions. This has the effect of improving the tracking performance for movement.

[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. Second
The figure is an explanatory diagram illustrating the principle of lens driving 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. 9th
The figure 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. 1st
FIG. 1 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. PRS...microcomputer, LCM...buffer circuit, SNS...sensor device.

Claims (1)

[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 amount of movement of the subject is determined based on the focus adjustment data in past focus adjustment operations based on the position of the subject after a predetermined time. An arithmetic circuit is provided that predicts and calculates the lens driving amount according to the image plane position using a high-order functional formula, and the lens is driven to focus on the subject position after a predetermined time, and the highest-order of the functional formula is a correction circuit that performs the predictive calculation using a correction function formula having a correction coefficient obtained by multiplying the coefficient by a predetermined value smaller than 1 and larger than 0; and a correction circuit that determines the reliability of the focus adjustment data and calculates the The present invention is characterized by providing a determination circuit that causes the correction circuit to perform predictive calculation using the correction function formula when the reliability is low, and causes the prediction calculation to be performed using the function formula before correction when the reliability of the data is high. Focus adjustment device.