JPH01288814A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To execute a focusing display even by a focusing device for executing a predictive operation by providing a prediction propriety deciding means and executing the focusing display immediately when it has been decided to be a followable object to be photographed by a prediction processing. CONSTITUTION:A prediction arithmetic circuit for deriving an image face position of an object to be phototraphed after a prescribed time, based on the defocus quantity DEF which has been derived by a focus detecting circuit plural times in the past, and is prescribed prediction propriety deciding circuit are provided in a controller PRS. In this state, in the prediction propriety deciding circuit, when it has been decided that correct focusing can be executed by driving a lens to the image face position, lighting of a focusing display is executed immediately by a light emission diode LED through a display use driving circuit DDR. Accordingly, by executing a follow-up correction, it can be eliminated to decide to be non-focusing in spite of a fact that the follow-up to the object to be photographed is executed exactly.

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, many automatic focus adjustment methods for eye reflex cameras (
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.

In such conventional devices, in-focus is determined when the amount of defocus determined by focus detection after driving the lens is zero.

However, during actual shooting, it is not necessary for the shooting lens to come to the exact in-focus position (there is no need for the amount of defocus to be zero), and the focus may vary depending on the lens's open F number and the aperture value at the time of shooting. If the amount (default force cutting 1) is less than or equal to the allowable amount (field depth), it can be considered that the focus is in focus. If the defocus amount is within the in-focus zone, it is determined that the camera is in focus, and an in-focus display is performed.

Furthermore, conventional devices try to focus on the subject by repeating the cycle of "focus detection (sensor signal input, focus detection calculation), lens drive" as described above, and the lens changes in each cycle. The amount of drive is based on the amount of defocus at the time of focus detection in that cycle, and it is expected that the amount of defocus at the time of focus detection will be eliminated when the lens drive is completed.

Therefore, as a matter of course, a considerable amount of time is required for focus detection and lens driving, so focus detection is necessary in the case of a subject with large movements.

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 problem,
The present applicant has proposed Japanese Patent Application No. 62-328233. The gist of the method presented in this proposal is to predict the defocus change caused by the movement of the subject and correct the lens drive amount, taking into consideration the detected defocus change in each cycle and the time interval of each cycle. (hereinafter referred to as follow-up correction), and from the viewpoint of focusing accuracy at the end of lens driving, this method is expected to improve the above problem.

However, when the tracking correction is actually performed, the following problem arises.

The operation of the tracking correction described above will be described below with reference to the drawings.

FIG. 2 is a diagram for explaining a lens driving method using tracking correction. 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 x(t ) and 1! When (1) matches, the image is in focus. And [t+, t+'] is the focus detection operation, [
t+', t+++] is the lens drive amount.

Further, in the conventional example shown in the figure, it is assumed that the image plane position changes according to a quadratic function. That is, time t
3, the current and past three image plane positions (t, +X
l ) (tz lX2 ) (t31X3 ), based on the above formula x(t) =at''+bt+c,
The image plane position X4 at time t4, which is TL (AF time lag+release time lag) after time t3, can be predicted.

However, what can actually be detected by the camera is image plane position XI.
+x2+x3, but the defocus amount DF.

DF2. DF3 and lens drive fl D L 1r D L2 in terms of image plane movement amount. and time t
4 is just a future value, and in reality, it is a value that changes as the storage time of the storage type sensor changes depending on the subject brightness, but for simplicity, it is assumed as follows.

t4 2 t3 = TL = TM2 + (release time lag)
(1) Under the above assumptions, the lens drive amount DL3 calculated from the focus detection result at time t3 is determined as follows.

x(t)=at2+bt+c (
2) Then, considering (till!I) in the figure as the origin, t, =Q Xl ==I)F',
(3) tz = TM 1x2 :I) F2
+ DLl (4) t3=TM1+TM2
x3=DF3+DL1+DL2 (5) (2) and (3)
, (4), and (5) to obtain a, b.

When calculating C, c=DF, (8
) Therefore, the lens drive fiDL3 converted to the amount of image plane movement at time t4 is: DL3=x4-13=x4-x3+DF3=a[(TM,+TM2+TL)'-(TM,+TM
2)"1+b-TL+I)F, calculated as (9).

When the lens is driven based on the above calculation results, the lens is controlled as shown in FIG. 3.

That is, in this method, the lens is driven while taking into account the AF time lag + release time lag and correcting the delay due to this time lag in advance.
At the end of lens driving, the lens is in a state in which it is ahead by the amount of follow-up delay DF caused by the release time lag. That is, when distance measurement is performed after lens driving is completed, the defocus amount DF is detected.

[Problem to be solved by the invention] In this way, when the above-mentioned tracking correction is performed on a moving subject, distance measurement is always performed with the focus being defocused by the amount of focus movement that changes during the release time lag. , the conventional method of determining focus, that is, determining that the camera is in focus if the detected amount of defocus is within a predetermined depth of field (focusing range), cannot accurately track the subject. The problem arises that it is determined that the camera is out of focus even though the camera is in focus.

[Means for solving problems]

In view of the above, the present invention provides a means for determining whether prediction is possible, and immediately displays an in-focus display when it is determined that the subject is one for which the lens can be driven by the prediction process, that is, a subject that can be tracked by the prediction process. Even in a focus adjustment device of the type that drives the lens through the above-mentioned prediction processing, the in-focus display is made possible.

In other words, when the image plane position after the release time lag and the lens position can match with the lens drive determined by the above prediction calculation, the in-focus display is performed even if the amount of defocus at that point is large. This solves the above problem.

〔Example〕

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

In the figure, PH1 is a camera control device, which includes, for example, a CPU (central processing unit), ROM, and RAM.

It is a 1-chip microcomputer with A/D conversion function. The computer PR8 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, PH1 is the synchronous communication signal So, SI, 5CLK, communication selection signal CLCM.
, C3DR, and CDDR to communicate with peripheral circuits and lenses within the camera body and control the operations of each circuit and lens.

SO is a data signal output from computer PR8,
SI is a data signal input to computer PR3, 5
CLK is a synchronization clock for signals so and sr.

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

That is, the computer PRS sets CLCM to H, and 5
When predetermined data is sent from SO in synchronization with CLK,
LCM connects 5CLK and S via the camera-lens interface.
The buffer signals LCK and DCL of o are output to the lens. At the same time, the buffer signal of the signal DLC from the lens is output as SI, and the computer PR3 outputs the buffered signal as 5CL.
In synchronization with K, the above SI is input as data from the lens.

The SDR is a drive circuit for the line sensor device SNS for focus detection, which is composed of a CCD, etc., and the signal C3DR is H.
', and P is selected using So, SI, and 5CLK.
Controlled from H1.

The signal CK is the COD drive clock φ1. The signal INTEND is a tarokk for generating φ2, and the signal INTEND is a signal that notifies PH1 that the accumulation operation has been completed.

The output signal O8 of the SNS is the clock φ1. It is a time-series image signal synchronized with φ2, and after being amplified by the amplifier circuit in the SDR, it is output to the computer PR3 as an AOS.

Computer PR3 inputs AOS from the analog input terminal, synchronizes with CK, and converts A/D using the internal A/D conversion function.
After conversion, the data is sequentially stored at a predetermined address in RAM.

5AGC, which is also the output signal of the sensor device SNS, is
AGC (automatic gain control: Aut) in the sensor device SNS.

It is the output of the sensor for Ga1n Control),
The signal is input to the drive circuit SDR and used for image signal accumulation control in the sensor device SNS.

SPC is a photometric sensor for exposure control that receives light from the subject through the photographic lens, and its output 5SPC is input to the analog input terminal of computer PR3, and
After D conversion, automatic exposure control (A
E).

DDR is a switch detection and display circuit, and the signal C
Selected when DDR is H', So, SI.

Controlled from PRS using 5CLK. That is, PRS
Display member D of the camera based on the data sent from
The display of the SP is switched and the on/off status of various operating members of the camera is notified to the computer PR3 by communication.

The LED is a light emitting diode that serves as an example of a display member DSP to indicate in-focus or out-of-focus, and indicates in-focus or out-of-focus by lighting or blinking.

The switches SWI and SW2 are switches that are linked to a release button (not shown), and when the release button is pressed to the first stage, SW1 is turned on, and when the release button is pressed to the second stage, SW2 is turned on. As will be described later, the computer PR3 performs photometry and automatic focus adjustment when the SWI is turned on, and
2-on is used as a trigger to control exposure and advance the film. Note that SW2 is connected to the "interrupt input terminal" of the microcomputer PR3, 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.

MTRI is for film feeding, MTR2 is for mirror up/
It is a motor for down and shutter spring charging,
Forward rotation/reverse rotation control is performed by each of the drive circuits MDRI and MDR2. PRS to MDRI.

Signals MIF, MIR, M2F input to MDR2
.

M2R is a signal for motor control.

MCI and MG2 are magnets for starting the running 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 PRS.

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.

LPR5 analyzes the instruction according to a predetermined procedure,
Focus adjustment and aperture control operations, as well as various lens parameters (open F number) from the output DLC.

(focal length, defocus amount vs. extension amount coefficient, etc.).

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.
Set R to 'L' to brake motor LMTR.

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

Further, when an aperture control command is sent from the camera, it is sent at the same time (according to the number of aperture stages), a stepping motor DMTR, which is known for driving the aperture, is driven.

Note that since the stepping motor can be controlled in an open manner, it does not require an encoder to monitor its operation.

ENCZ is an encoder circuit attached to the zoom optical system, and the in-lens control circuit LPR3 is the encoder circuit ENC.
The zoom position is detected by inputting the signal 5ENCZ from Z. Lens parameters at each zoom position are stored in the in-lens control circuit LPR3, and when requested by the camera-side computer PR3, 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. 5 and subsequent figures.

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

FIG. 5 is a flow chart showing the overall flow of the above program. When the program execution starts with the above operation, it passes through step (001) and then step (002).
), the state of the switch SWI, which is turned on by pressing the first step of the release button, is detected, and when the SWI is off, the process moves to step (003), and control flags and variables set in the RAM in the computer PRS are detected. Clear all and initialize.

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

In step (005), a "photometering" subroutine for exposure control is executed. The computer PR3 inputs the output 5 spc of the photometric sensor SPC shown in FIG. 4 to an analog input terminal, performs A/D conversion, and obtains an optimal shutter control value from the digital photometric value.

The aperture control value is calculated and stored at a predetermined address in the RAM. During the release operation, the shutter and aperture are controlled based on these values.

Subsequently, in step (006), the "image signal manual input" subroutine is executed. The flow of this subroutine is shown in FIG. 6, and the computer PR3 inputs an image signal from the focus detection sensor device SNS.

Details will be described later.

In the next step (007), the defocus amount DEF of the photographing lens is calculated based on the input image signal. The specific calculation method is disclosed in Japanese Patent Application No. 61-16082 by the applicant.
Since it is disclosed in Publication No. 4 etc., detailed explanation will be omitted.

In step (008), a "prediction calculation" subroutine is executed. This "prediction calculation" subroutine corrects the lens drive amount, and details will be described later.

In the next step (009), a "lens drive" subroutine is executed, and the lens is driven based on the lens drive amount corrected in the previous step (008).

The flow of this "lens drive" subroutine is shown in FIG. After the lens drive is completed, the step (00
2), and steps (005) to (009) are repeatedly executed until SWl is turned off or the second stroke SW2 of the release switch (not shown) is turned on, thereby achieving a preferable focus even for a moving subject. Adjustments are made.

Now, when the release button is pressed further and the switch SW2 is turned on, the interrupt function immediately shifts to step (010) and starts the release operation, regardless of which step it is in.

In step (011), it is determined whether the lens is being driven. If it is, the process moves to step (012), where a lens drive stop command is sent to stop the lens, and the process moves to step (013), where the lens is stopped. If it is not being driven, the process immediately proceeds to step (013).

In step (013), the quick return mirror of the camera is raised. This is executed by controlling the motor control signals M2F and M2R shown in FIG. In the next step (014) ('! Previous step (
In the photometry subroutine (005), the aperture control value already stored is multiplied by the SO signal and sent to the in-lens control circuit LPR3 via the circuit LCM to perform aperture control.

Whether or not the mirror up and aperture control in steps (013) and (014) have been completed is detected in step (015), 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 (016).

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

When the shutter control is completed, the next step (017) is to send a command to the lens to open the aperture using the communication operation described above, followed by step (018).
) to perform a mirror down. Mirror down is the same as mirror up using motor control signal M2F.

This is executed by controlling motor MTR2 using M2R.

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

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

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

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

"Image signal manual" is an operation executed at the beginning of 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 (8).
Update the contents of M, , TM2.

That is, in step (103), the memory TN stores the current focus detection start time TN detected in step (102).
is input, so the next time the image signal input subroutine is executed, TN and -TN become the previous focus detection time interval. Therefore, memory T at TM2←TN, -TN
The previous time interval is M2, and TM.

←The previous time interval is stored in the memory TM at TM2. In this way, by executing step (103), formula (6)
, (7) and (8), the previous time interval is always stored in memory TM, and TM2 is always stored with the previous time interval.

Now, in the next step (104), the sensor device SNS is caused to start accumulating optical images. Specifically, the microcomputer PRS sends an "accumulation start command" to the sensor drive circuit SDR via communication, and in response to this, the drive circuit SDR issues a clear signal CLR of the photoelectric conversion element section of the sensor device SNS.
is set to L' to start charge accumulation.

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 of the computer PR3 is detected, and it is determined whether or not the storage has been completed. The sensor drive circuit SDR sets the signal INTEND to L' at the same time as the start of accumulation, monitors the AGC signal 5AGC from the sensor device SNS, and when the 5AGC reaches a predetermined level, sets the signal INTEND to H' and simultaneously sets the charge transfer signal SH. It has a structure in which the charge in the photoelectric conversion element section is transferred to the CCD section at a predetermined time 'H'.

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 M A When TE becomes MAXINT or more, STEP (109
) and force the accumulation to end.

To complete the forced accumulation, send a message from computer PR3 to circuit SDR.
This is executed by sending the "accumulation end command". SD
When R receives the "accumulation end command" from PH1, it sets the charge transfer signal SH to IH1 for a predetermined period of time to transfer the charge in the photoelectric conversion section to the CCD section. The sensor accumulation ends in the flow up to step (109).

In step (110), the image signal O8 of the sensor device SNS is
A/D of signal AO3 amplified by sensor drive circuit SDR
Performs conversion and stores the digital signal in RAM. To explain in more detail, the SDR uses the COD driving clock φ1. in synchronization with the clock CK from PH1. φ2 is generated and given to the sensor device SNS, and the sensor device SNS generates φl.
, φ2, 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 drive circuit SDR, it is input as AO3 to the analog input terminal of the computer PR3.

The computer PRS outputs its own clock CK.
A/D conversion is performed in synchronization with , and the digital image signals after A/D conversion are sequentially stored at predetermined addresses in the RAM.

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

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

When this subroutine is executed, step (202)
communicates with the lens at
Enter THJ. rSJ is the "coefficient of defocus amount versus focusing lens extension amount" specific to the photographic lens,
For example, in the case of a single lens that extends entirely, S=1 because the entire photographic lens is a focusing lens, and in the case of a zoom lens, the control circuit LPR3 is adjusted according to each zoom position detected by the encoder ENCZ. Determine S. rPTHJ is the amount of protrusion of the focusing lens per 1 output pulse from 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).

In the next step (206), 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. This lens drive completion detection is performed by the control circuit LP as described above.
A counter in R3 counts the pulse signal of the encoder ENCF, and the process is executed by detecting whether or not the count value matches the lens drive amount FP through the above-mentioned communication.

Next, the flow of the "prediction calculation" subroutine will be explained using FIG. FIG. 1 shows the flow of the "prediction calculation" subroutine, in which it is determined whether prediction calculation is possible or not, and if prediction is possible, the lens drive amount is calculated in consideration of the AF time lag and release time lag.

Step (302) is a counter C0UNT for determining whether data necessary for prediction has been accumulated.
Determine whether to count up or not.

In this embodiment, if three or more distance measurement data and lens drive data have been accumulated, that is, if C0UNT>2, predictive calculation is possible, and no further count-up is necessary. Step (304
). Also, if C0UNT<3, step (3
After counting up C0UNT in step 03), step (
Proceed to 304).

In step (304), data for the current prediction calculation is updated. That is, the prediction calculation is (6).

Since it is performed based on equations (7), (8), and (9), the data includes the current defocus amount DF3 in Fig. 2, the previous and previous defocus amounts DF2゜DF
,, Previous lens drive amount DL1, Current lens drive amount D
L2, the previous and previous time intervals TM1°1M2, and the expected time lag TL are required. Therefore step (30
In 4), each time focus detection is performed, the currently detected defocus amount DF is input into the storage area DF on the RAM,
The previous defocus amount is input into the storage area DF2, the previous defocus amount is input into the storage area DF, and the previous lens drive amount DL converted to the image plane movement amount is input into the storage area DL2.
The lens drive amount DL converted from the previous image plane movement amount is input into the storage area DL1, and the data in each storage area is updated to the data necessary for the current prediction calculation. As for the previous lens drive amount DL, the current lens drive amount obtained in step (316), which will be described later, is used as the previous drive amount data at the time of the next prediction calculation.

In step (305), it is determined whether data necessary for the prediction calculation has been input to each of the storage areas. As shown above (prediction calculation is done this time, last time.

The previous defocus amount and the previous and previous lens drive amounts are required, and the condition is that the focus adjustment operation has been performed three or more times in the past. Therefore, each time a focus adjustment operation is performed in step (303), the counter C0UNT is
+1 is added to the counter, the counter counts the number of times the focus adjustment operation has been performed, and it is determined whether the number of times is greater than 2, that is, whether or not the operation has been performed three or more times. If the predictive calculation is possible, the process proceeds to step (306), and if it is not possible, the process proceeds to step (319).

In step (306), a "prediction/non-prediction determination" subroutine determines whether the defocus amount detected this time is suitable for prediction. If this "prediction/non-prediction determination" subroutine determines that the data in the storage area used for prediction is not suitable for prediction, step (
The process moves to step 307), and if it is determined that it is suitable for prediction, the process moves to step (312).

If it is determined in step (306) that it is not suitable for prediction calculation and the process moves to step (307), distance measurement is performed again without prohibiting prediction immediately, and if it is still not suitable for prediction calculation, prediction is performed. It is designed to prohibit calculations.

This is because when a photographer chases a moving subject, if the subject moves out of the range-finding field of view and range-finding is performed on another subject, or when another subject passes in front of the main subject. If the value is different from the defocus amount that should be obtained and it is determined that it is not suitable for prediction,
In order to perform the predictive calculation again, the focus adjustment operation must be performed three times or more in the past, and the predictive calculation cannot be restarted immediately.

Therefore, in this embodiment, even if it is once determined that the image signal is not suitable for prediction, the image signal is captured again by the "image signal manual input 2" subroutine in step (307). This subroutine will be explained later. When this step is completed, the process moves to step (308).

In step (308), focus detection calculation is performed based on the image signal obtained in step (307), and the defocus amount DF is
Calculate.

In the next step (309), it is determined that the previously detected defocus amount DF3 is not suitable for the prediction calculation, so this DF3 is updated to the currently detected defocus amount DF, and the process moves to step (310).

Step (310) is the same "prediction/non-prediction determination" subroutine as step (306), and if it is determined that the data is suitable for prediction calculation, step (311) is performed.
The process proceeds to step (319), where a predictive calculation is performed, and if it is determined that it is not suitable, the process proceeds to step (319), and the predictive calculation is prohibited.

In step (319), it is determined that the prediction is unsuitable twice in a row, and in order to prohibit (reset) the prediction, the counter C0UNT representing the accumulation state of data necessary for the prediction is set to O(
reset).

In the next step (320), it is determined that the prediction is unsuitable, that is, accurate tracking correction cannot be performed, so a "prediction NG display" is performed. Here, as an NG display method, the photographer is notified of the unpredictability by blinking the LED in the viewfinder.

Then, in the next step (321), the lens drive amount DL when no predictive calculation is performed is calculated. Here, DL is similar to conventional servo AF, DL=DF (step (30
It is calculated as the defocus amount obtained in 8).

In step (311), the expected time lag TL necessary for performing the predictive calculation is calculated, but at this time, the expected AF
The time lag (time required for focus detection and lens drive) is not 1M2 (TM, TR (release time lag)).
Use the sum of Since distance measurement is performed twice in the time TM2 from the previous focus detection to the current focus detection, this is longer than the actual predicted current AF time lag (estimated). The time TM from the previous focus detection to the previous focus detection was used.When this step is completed, the process moves to step (313).In addition, TL in step (311) is (TM2+TM2)/2+
TR is also fine.

If it is determined in step (306) that prediction is possible and the process moves to step (312), the expected time lag TL is calculated in step (312). As mentioned above, the storage area TM2 stores the time from the previous focus detection operation to the current focus detection operation, and the time required for the current focus adjustment is also 1M.
The time lag TL is based on the assumption that it is consistent with 2.
Find =TM2+TR.

In the next step (313), the prediction determination means determines that prediction is possible and that accurate follow-up correction is possible, so that an in-focus display is performed. Here, as an in-focus display, an LED in the finder is turned on to notify the photographer that tracking correction is being performed accurately.

In the next steps (314) and (315), each storage area DF, ~DF, DL, DL2. Based on the data stored in TM, 1M2, a in equations (6) and (7),
A and B representing the b term are determined, and the process moves to step (316).

In step (316), data of each storage means and step (311) or (312) and step (314) are stored.
), (315), calculate the calculated value of equation (9), and use this as the lens drive amount DL in terms of the current image plane movement amount.
seek.

In the next step (317), the lens drive amount DL found in step (316), the open F number FN of the photographing lens, and a predetermined coefficient δ (0.035 mm in this example) are determined.
The product FN・δ is compared, and if DL<FN・δ, the process moves to step (318);
2) Return.

In step (318), in the previous step (317),
It is determined that the lens drive amount DL is smaller than the image plane depth FN·δ, that is, there is no need to drive the lens, the lens drive amount DL is set to O, and driving of the lens is prohibited. This eliminates unnecessary minute lens drive (and improves both usability and power consumption.Also, in this example, FN is the open F number of the photographic lens.
There is no problem even if this is the shooting aperture value (, δ is also 0,
It is not limited to 0.035 mm. When this step is completed, the subroutine is returned to the next step (320).

In this embodiment, the prediction calculation is prohibited when it is determined that the prediction calculation is not suitable twice in a row, and data accumulation is started again. However, considering the response of the AF system, The prediction may be prohibited after one judgment (or the prediction may be prohibited when it is judged as inappropriate two or more times in a row).

Next, the flow of the "prediction/non-prediction determination" subroutine will be explained. FIG. 8 shows the flow of the "prediction/non-prediction determination" subroutine, and step (402) is "continuity determination of image plane position" for detecting continuity of the image plane (subject position). This subroutine determines whether the camera is continuously measuring the distance to the same subject, and the details will be described later.

If it is determined in this step that the image plane position is changing continuously, the process moves to step (403); otherwise, it is determined that another subject has been measured, and the process proceeds to step (406).
Proceed to and return.

Step (403) is a "focus detection accuracy calculation" subroutine that evaluates the reliability of the focus detection result.

In this step, it is determined whether the defocus amount used in the prediction calculation is reliable enough to be used in the prediction calculation. If it is determined that the defocus amount is reliable enough to be used in the prediction calculation, the process moves to step (404), and if it is determined that the reliability is low. If so, the process moves to step (406) where the prediction calculation is stopped and the process returns.

Step (404) is a "predictive AF suitability determination" subroutine for determining whether the subject or condition is effective for predictive AF, and the details will be described later.

In step (404), it is determined whether or not the predictive calculation has an effect or has the opposite effect when the lens is driven based on the budget calculation result. If the condition is met, the process moves to a step (406) of stopping the prediction calculation, and if necessary, a step (406) of enabling the prediction calculation.
05) and return.

Here, in this example, we evaluated "continuity of image plane position,""focus detection accuracy," and "appropriateness of predictive AF" broadly, and predicted calculation was possible when all of these conditions were satisfied. Furthermore, [Lens drive accuracy J l' - AF time lag variation j, etc. may be added for judgment, or the number of judgment items may be reduced to one in order to emphasize response and shorten calculation time. is also possible.

Furthermore, in the "prediction/non-prediction determination", the order of subroutines for each determination is such that the routine with the shortest determination time is performed first. Alternatively, by performing a routine with a high probability of being determined as non-prediction first, it is possible to shorten the processing time for prediction and non-prediction determination.

Next, the "continuity determination of image plane position" subroutine in step (402) of the "prediction/non-prediction determination" subroutine shown in FIG. 8 will be explained using FIG. 9.

Step (502) is based on the data of each storage area (D
The following calculation is performed: F2+DL, -DF, )/TM. This calculation is a step for calculating the average value vl of the image plane movement speed between times t1 and t2 in FIG.

The calculation in the next step (503) is similarly performed at times t2 and t.
This is a step of calculating the average value v2 of the image plane movement speed between the three images. After this, the process advances to step (504).

In step (504), step (502), (
The absolute value VA of the difference between the image plane movement velocities Vl and V2 obtained in step 503) is calculated, and the process moves to step (505).

In step (505), the VA determined in step (504) is compared with a preset number AX, and VA is
When VA is larger than X, it is judged that there is no continuity in the image plane position, and when VA is smaller than AX, it is judged that there is continuity.

The principle of determining prediction or non-prediction using the above flow is based on the fact that if the same subject is being tracked, the image plane movement speed at that time will also change continuously.

Therefore, we calculate the temporally adjacent image plane movement speeds, and if the difference is small, it is assumed that the image plane movement speeds are changing continuously, and it is determined that the same subject is being measured. It has been determined that it is possible to perform focusing using predictive calculations. On the other hand, if the change in the image plane movement speed is sufficiently large, it is assumed that the image plane movement speed is not changing continuously, and it is determined that a different subject has been measured, and the focus is adjusted by predictive calculation. It is determined that it is not possible.

, FIG. 10 shows the flow of another embodiment of the "continuity determination of image plane position" subroutine.

This is because if the absolute value of the detected defocus amount DF is thicker than a certain value BX, it is determined that another object has been measured, and predictive calculation is prohibited.

That is, when tracking and distance measuring the same subject, the detected defocus amount rarely changes significantly, and when the detected defocus amount is larger than a predetermined value, it is determined that there is no continuity.

To determine the continuity of these image plane positions, if you are continuously measuring the same subject, you can focus by performing predictive calculations, but if you are measuring the distance of another subject, predictive calculations are not possible. We focus on this fact, and use this judgment to determine whether or not focusing is possible using predictive calculations.

The flow of the "focus detection accuracy determination" subroutine shown in FIG. 8 will be explained using FIG. 11.

Step (802) is the previous step (006) or (3)
Contrast value C for the image signal captured in 07)
This is a "contrast calculation" subroutine for calculating RT, and the method of calculating the contrast value is well known, and its explanation will be omitted here.

In the next step (803), the contrast value CRT obtained in step (802) is compared with a certain number CRA, and CR
If T>CRA, it is determined that the contrast of the image signal is thick (the focus detection accuracy is also high), and the process proceeds to step (804); otherwise, the detection accuracy is determined to be low, and the process proceeds to step (806). Return.

In step (804), the image signal accumulation time TE is compared with a certain number TZ1, and if TE<TZ, it is determined that the accumulation time is short and the focus detection accuracy is high, and the process proceeds to step (805) and returns. If not, there is a possibility that the image plane will move significantly during accumulation, and the reliability of the focus detection result is low, so the process proceeds to step (806) and returns.

Here, in this example, focus detection accuracy was evaluated only by contrast and accumulation time, but other methods, such as reliability thresholds such as the coincidence degree of two images and abnormalities in image signals due to ghosts, etc., were used to evaluate the focus detection accuracy. The reliability of the detection results may also be evaluated.

The flow of the "predictive AF suitability determination" subroutine shown in FIG. 8 will be explained using FIG. 12.

In step (902), a parameter LX indicating reversal or non-reversal of the lens driving direction between the previous and previous times and the previous and previous times.

In order to update the data in LX, move the value of LX2 to LX. This is because the data used for the previous prediction AF suitability judgment remains in the LXl, so in order to make the current judgment, it is necessary to invert or non-reverse the lens drive direction of the previous and previous previous and previous previous judgments. Input the value of LX2 shown in LX.

In the next step (903), the previous lens drive fiD
LX is calculated from L and the previous lens drive amount using the following equation.

LX=l DL21-I DL2-DL, In the l step (904), it is determined from the LX obtained in the step (903) whether or not the lens drive direction of the previous and previous lens drive directions is reversed or not. Here, if LX>0, IDL21>ID
L2-DL, l means 1, which means DL2 and D
This holds true when L and have the same sign. That is, the condition LX>O means that the driving direction of the lens is not reversed. On the other hand, if LX<0, it can be determined that the lens drive direction is reversed. In this step, if it is determined that the lens drive direction is not reversed, the process proceeds to step (906), and if it is determined that it is reversed, the process proceeds to step (905).

In step (906), rOJ indicating non-inversion is input to parameter LX2 indicating reversal or non-inversion of the driving directions of the previous and previous lenses, and in step (905) rlJ indicating reversal is input.

Then, in the next step (907), it is determined whether the lens drive direction has been reversed twice in a row. LX,
+LX2=2(7), that is, LX,=1°Lx2
If = 1, it means that the image has been inverted twice in a row, and considering that such a state is not a suitable subject or condition for predictive AF, step (912) is performed.
Proceed to and return. On the other hand, if there is no continuous reversal, it is considered suitable for prediction, and step (908)
Proceed to.

Step (908) is a subroutine that detects the distance between the subject and the camera. Methods for this include measurement using an external distance measuring device such as active AF, the focal length of the photographic lens, and the lens (extension position and defocus amount). Methods such as obtaining it from the distance value or directly obtaining it from the distance value in a distance ring may be considered, but the details thereof will be omitted in this embodiment.

In the next step (909), the subject-camera distance DZ obtained in step (908) is converted to the focal length F of the photographing lens.
Calculate the value LZ divided by L.

In step (910), L obtained in step (909)
If LZ<200 for Z, it is determined that the subject is suitable for prediction, and the process proceeds to step (911) and returns. If LZ<200, it is determined that the probability that the image plane movement speed is high is low and predictive AF is not necessary, and the process proceeds to step (912) and returns.

Here, in the determination based on the distance between the subject and the camera, 200 times the focal length of the photographing lens is used as a guide, but this may be any other value, or may be a value that changes depending on the moving speed of the subject, the lens, or the brightness of the subject.

Further, in this embodiment, the determination was made based on whether the lens drive direction is reversed or not reversed and the distance between the subject and the camera, but the determination may be made using either one of the determining means.

In addition, in this example, it was determined that it was inappropriate for prediction when the lens driving direction was reversed twice in a row, but this is because there are relatively many shooting scenes where the lens driving direction is reversed once. For example, when photographing a swing or when a person or vehicle passes nearby, the driving direction of the lens is reversed once.

In such a case, if prediction is immediately prohibited, it will take time to make the next prediction, resulting in disadvantages such as missing a photo opportunity, so in this example, the lens drive direction is We set it to prohibit prediction when the value is reversed, but considering the above reasons,
If the lens drive direction is reversed two or more times, for example, three or four times, it may be determined that the prediction is inappropriate.

FIG. 13 shows the flow of the "image signal human power 2" subroutine of step (307), and this "image signal human power 2" subroutine will be explained.

The flow of the subroutine in FIG. 13 is the step (1003
) (1004) is the same as the "image signal input" subroutine in FIG. 6, and here step (1003)
Only (1004) will be explained, and other explanations will be omitted.

Step (1003) is a step of calculating the current distance measurement time interval TM2 from the previous time, but in this case, the "image signal input" in step (006) and step (0
Since the previous defocus amount DF3 obtained by the "focus detection calculation" in 07) has been determined to be inappropriate for the prediction calculation, here the distance measurement time interval from the previous to the current distance measurement is set to 1M.
Must be 2.

Therefore, the sum of the ranging time interval TM2 from the previous time to the previous time and the ranging time interval TN, -TN from the previous time to this time is set to 1M2.

In the next step (1004), the current distance measurement start time TN
is input to TN, and the process moves to the following flow.

In each of the above-described flows, lens driving and in-focus/out-of-focus display are performed based on predictive calculations, and an overview of the overall operations will be explained below.

Step (005) in Figure 5 when switch SWl is turned on.
The flow from to (009) is executed. In the first and second executions of this step, the count value of the counter C0UNT in the prediction calculation subroutine of FIG. 1 is 1.
or 2, so the lens drive amount is in steps (3
DL determined in step 21), that is, the defocus amount DF obtained by the focus detection calculation in step (007) immediately before the prediction calculation subroutine is performed, becomes the lens drive amount. Therefore, in the first and second focus detection operations, the lens is driven based on the defocus amount obtained in the previous focus detection.The third and subsequent steps (005) to (
In the execution of step 009), since the counter C0UNT≧3 at step (305) in the prediction calculation subroutine, the steps after step (306) are executed. Therefore, in the focus detection operation after the third time, step (3
If it is determined in step 06) that predictive calculation is possible, step 3
12) to (318) are executed. Therefore, formula (6) ~
Through the predictive calculation process (9), the lens driving amount to the expected image plane position after the AF time lag and the release time lag is determined, and the lens is driven in advance of the release time lag shown in FIG. 3 described above. Also, at this time, an in-focus display is performed.

The above operation is repeated and the lens is driven to the expected position as shown in FIG.
If it is determined in step 6) that the lens cannot be brought into focus by driving the lens using predictive calculation in the flow shown in FIGS. 8 to 12, step (307) is performed.
Proceed to the next step. Therefore, in this case, the focus detection operation is performed again based on the image signal obtained in the "image signal manual input 2" subroutine of FIG. 13, and it is determined again in step (310) whether predictive calculation is possible. Ru.

Then, if it is determined that the focus cannot be achieved by lens driving based on the predictive calculation processing based on the remeasured distance data such as the re-defocus signal obtained in step (308), the steps proceed to (319) to (321). Then, the prediction NG is displayed, and the lens is driven according to the defocus amount obtained in the re-measurement, and the subsequent focus detection operation returns to the initial focus detection operation state and repeats the above operation again. .

In addition, if it is determined that predictive calculation is possible in step (310), step (310) is performed.
Steps (313) to (31g) are executed via step 11), and lens driving and focus display (predicted OK display) are performed by the above-described predictive calculation processing.

Next, as the prediction/non-prediction determination subroutine described above, the continuity of the image plane position is determined based on the coefficients of the quadratic function obtained by predictive calculation and the amount of lens drive, and the continuity of the image plane position is predicted based on the reliability of each distance measurement data and the amount of lens drive. A method for evaluating accuracy and determining whether prediction is possible based on these parameters will be explained. The overall system, sequence, and main flow of the camera when this method is used are the same as those in the above-mentioned embodiment, so their explanation will be omitted here, and only the "prediction calculation" subroutine according to the above method will be explained.

Figure 14 shows the flow of the "predictive calculation" subroutine using the above method, in which it is determined whether the predictive calculation is possible, and if it is possible to predict, calculates the lens drive amount taking into account the AF time lag and release time lag. It is something.

Steps (1301) to (1305) are the same as steps (301) to (305) in FIG. 1, and their explanation will be omitted.

Steps (1306) to (1309) are similar to steps (312) and (314) to (316) in FIG.
When focus detection is performed three or more times in these steps, the lens drive amount DL is determined by predictive calculation.

Step (1310) is a prediction/non-prediction determination subroutine in which it is determined whether or not prediction is possible, as will be described later. If prediction is possible, in-focus display is performed in step (1311). This display is performed by driving the LED or the sounding body in the same manner as in FIG. Steps (1312) to (1
325) is the same as steps (317) to (322) in FIG. 1, and the explanation thereof will be omitted.

In the above steps, for the third and subsequent focus detection operations, lens drive and focusing instructions are given based on predictive calculations.

Further, when it is determined in step (1310) that the lens driving based on the predictive calculation does not result in focus, step (1310) is performed.
314) to (1317). This step is similar to steps (307) to (309) and (311) in FIG. 1, so its explanation will be omitted. Then step (131
8) to (1320) are performed. This step is (13
07) to (1309), so step (1
Based on the distance measurement result obtained in step 315), the lens drive amount DL is determined again using equations (6) to (9).

After the lens drive amount is determined again, step (132
In step 1), the same prediction/non-prediction determination subroutine as in step (1310) is carried out again, and when it is determined that prediction is not possible, steps (1322) to (1324) and (1312) to (
1325). This step is the same as steps (319) to (321) and (317) to (322) in FIG. Lens driving is performed based on the defocus amount obtained from the detection results. If it is determined in step (1321) that predictive calculation is possible, the process proceeds to step (1311) and subsequent steps to display focus and drive the lens by the amount of lens drive determined by the predictive calculation in step (1320).

FIG. 15 shows the flow of the "prediction/non-prediction determination" subroutine shown in FIG. 14.

Step (1102) is a "predictive AF suitability determination" subroutine. This subroutine is the same as that in FIG. 8, and detailed explanation will be omitted. Prediction A at this step
When it is determined that the conditions are such that the effect of F occurs, step (
If not, it is determined that the prediction is inappropriate, and the process proceeds to step (1106) to return.

Step (1103) is a "prediction accuracy determination" subroutine, the details of which will be described later. In this step, data DF, ~DF3. The accuracy of DL, DL 2 is evaluated, and the reliability of the predicted value is evaluated from the accuracy of the entire data. If it is determined in step (1103) that the predicted calculated value is highly reliable, the process moves to Stellar P (1104); otherwise, it is judged that it is unsuitable for prediction, and the process proceeds to step (1106) and returns.

Step (1104) is a "continuity determination of image plane position" subroutine. This subroutine will be described later, but in this step, it is determined whether the photographer is following the same subject based on the continuity of the image plane position, and if it is determined that there is continuity, the state is suitable for predictive calculation. After making a judgment, the process proceeds to step (1105). If not, it is judged that the prediction is inappropriate, and the process proceeds to step (1106) and returns.

Here, the reason why "judgment of prediction accuracy" was placed before "judgment of continuity of image plane position" is because each data is highly reliable (if not
The reliability of the image plane position determined using these data is low (
, is not worth evaluating, so this example has a flow with such a judgment order.

However, these judgment orders may be other than those in this embodiment, and the number of judgment items may be reduced depending on the case.

FIG. 16 shows the flow of the "prediction accuracy determination" subroutine shown in FIG. 15, and the "prediction accuracy determination" subroutine will be explained with reference to this diagram.

Step (1202) is a parameter CR representing the previous and previous distance measurement accuracy, and the previous and previous lens driving accuracy.
,,CR2,LX, data is being updated.

This is because the data used in the previous judgment remains, so in order to judge the prediction accuracy this time, the old data must be updated with new data. Therefore, the value of CR2 is set to the parameter CR, which represents the previous distance measurement accuracy, and the value of CR3 is set to the parameter Lx1, which represents the previous lens drive accuracy.
The value of 2 is entered.

Here, CR, , CR2, and CR3 are D in Fig. 2, respectively.
F,,DF2. It is a parameter representing the focus detection accuracy of DF3, and LX, , LX2 are DL, DL2, respectively.
This is a parameter that represents the lens driving accuracy.

In the next steps (1203) and (1204), if DL or DL2 is O, an erroneous judgment will be made when determining the subsequent lens drive direction, inversion, or non-inversion.
If L or DL2 is O, it is determined that the driving direction has not been reversed, and the process moves to step (1207).
Otherwise, the process moves to step (1205).

In steps (1205) and (1206), the driving direction of the lens is determined in the same way as the lens driving direction, inversion, and non-inversion determination in FIG.
Proceed to 8) and set the parameter LX2 that represents lens drive accuracy.
Input rlJ to , and if it is non-inverted, step (1207
) and input rOJ to LX2.

If the driving direction of the lens is reversed here, lens driving accuracy will be reduced due to backlash in the lens driving system. Therefore, in this embodiment, when the lens driving direction is reversed, it is determined that the lens driving accuracy is low, and the parameter Lx2 is set to rl.
J is input, and if it is non-inverted, it is determined that the drive accuracy is high, and "0" is input to LX2. i.e. LX2 and LX
When the value of , is "1", the accuracy is poor (and when the value is "O", the accuracy is good.

In the next step (1209), the contrast CRT of the image signal used for the current focus detection is calculated. Then, in the next step (1210), the CRT calculated in step (1209) is compared with a certain number CRA, and if CRT>CRA, the process proceeds to step (1211); otherwise, the process proceeds to step (1216). Here, CRA is the value of the low contrast limit of the focus detection system, where CRT<
If it is CRA, it is determined that focus cannot be detected, and step (12)
In step 16), "3" is input to the parameter CR, which indicates the current focus detection accuracy, and the process returns in step (1220). On the other hand, if focus detection is possible, step (1
211).

In step (1211), contrast CRT is compared with a certain number CRB, and if CRT>CRB, step (1211) is performed.
212), otherwise step (1215)
, inputs "2" into the detection accuracy evaluation parameter CR3, and proceeds to step (1217). Step (121
If it is determined in 1) that the focus detection accuracy is above a certain level (CRT>CRB), the process moves to step (1212).

In step (1212), the contrast CRT is compared with a certain number of CRCs, and if CRT>CRC, it is determined that the focus detection accuracy is very high, and the process proceeds to step (1213).
Enter “0” in CR3, otherwise step (1
214), enter "1" in CR3, and proceed to step (1
217).

Here, the smaller the value of CR3, the higher the detection accuracy. Note that CRA<CRB<CRC is set. In step (1217), the sum CRX of parameters indicating each focus detection accuracy and lens drive accuracy is calculated.

In the next step (1218), CRX is compared with a certain number CZ, and if CRX<CZ, it is determined that the data is reliable in terms of total accuracy, and the process proceeds to step (1219) and returns. On the other hand, if this is not the case, it is determined that the predicted value is unreliable, and the process moves to step (1220) and returns.

In this embodiment, the total accuracy of each data was evaluated as the prediction accuracy, but as another method, the evaluation may be performed based on the time interval or the actual prediction calculation formula.

For example, it is effective to reduce the value of CZ when TL is large with respect to TM, 7M2, and to increase it in the opposite case. Also, to detect xI+x2+X3 in Fig. 2, Xi :I) F'.

x2 ==I) I,, +DF2 X3: I) L, , +DL2 +DF3.

Therefore, CRX=(CR, “+CR2”+LX, “+CR3”+
LX, "+LX2").

In addition, in this embodiment, accumulation time, ghost, and temperature are also considered.

The evaluation may be performed taking into account factors that affect focus detection accuracy, such as humidity.

Furthermore, regarding lens drive accuracy, if evaluation based on lens drive method, lens configuration, and lens ID is added, more effective accuracy evaluation becomes possible.

Next, a subroutine for determining the continuity of the image plane position used in step (1104) in FIG. 15 using parameters obtained by predictive calculation will be described.

Figure 17 shows the coefficient A of the quadratic term obtained by the predictive calculation.
12 is a flowchart illustrating an example of a subroutine of "continuity determination of image plane position" in which continuity is determined based on the value of .

In step (702) in FIG. 17, the difference AB between the coefficient A found by the current prediction calculation and the coefficient A1 of the quadratic term of the prediction function found by the previous prediction calculation is calculated.

However, this A1 will be input to A every time a new A is found in step (704), so it will be updated every time A is found, and it will always be the same as that found in the previous focus detection operation. Coefficient A has been input.

In step (703), the absolute value of AB and the constant value FX are
When l AB l <FX, the process proceeds to step (704), where the above-mentioned coefficient A is updated and it is determined that there is continuity.

If the absolute value of AB is greater than FX, the process moves to step (706) and it is determined that there is no continuity.

The determination principle shown in FIG. 17 is that if the same subject is being measured, the image plane position will change continuously, and at this time, the coefficients of the prediction function will also change continuously, and the prediction function The change in the coefficient A of the quadratic term is examined, and it is determined that prediction is possible when the change in the value of A is small.

Here, we focused only on the coefficient A of the second-order term, but it may be determined based on the coefficient B of the -th-order term or the change in the coefficients of the first-order and second-order terms. That is, a of the prediction function x (t) in FIG.
Since the term or b term does not change significantly with each focus detection operation for the same subject, the continuity of the image plane position is determined by detecting the rate of change of the a term or b term. There is.

FIG. 18 shows another "continuity determination of image plane position" subroutine, and its flow will be explained.

The principle shown in Fig. 18 is that when the subject being measured moves to another subject mid-way, this effect is more clearly expressed in the quadratic term A than the linear term B of the prediction function, and the value of A is Focusing on the fact that the absolute value becomes very large, it is determined whether continuity exists or not based on the absolute value of the value of A.

In step (712), if the coefficient A of the quadratic term of the prediction function is greater than a certain number CX, the process proceeds to step (713);
Otherwise, the process moves to step (716) and it is determined that there is no continuity. However, the arbitrary number Cx is a negative number.

In step (713), when the coefficient A of the quadratic term of the prediction function is larger than a certain number DX, it is determined that there is no continuity, and the process proceeds to step (716), and when A is smaller than DX, step (
715) and it is determined that there is continuity. However, DX is a positive number.

FIG. 19 is a flowchart showing an example of another [continuity determination of image plane position] subroutine, and this flow is for determining whether prediction is possible from a change in the lens drive amount.

In step (722), if the absolute value of the current lens drive amount DL is greater than a predetermined value EX, step (723)
), otherwise the process moves to step (724). In step (723), the previous lens drive f
! Compare whether the absolute value of kDL2 is larger than a predetermined value Ex2, and if lDL21 > EX2, step (
725), otherwise step (724)
Move to.

In step (725), considering that the values of DL and DL2 are relatively large and the image plane position is moving quickly, DL and D
Continuity is determined from the ratio of L2. That is, DL and DL
If the ratio of 2 is close to 1, it is considered that there is continuity, and in this step, DC=DL/DL2-1 is calculated.

Then, in the next step (726), if the value of DC is smaller than the predetermined value EX4, it is determined that there is continuity, and the process moves to step (727) and returns; otherwise, it is determined that there is no continuity, and step ( 728) and return.

In step (724), considering that DL or DL2 is relatively small and the image plane position has not changed much, DL
Continuity is determined based on the difference between and DL2.

That is, if the difference between DL and DL2 is smaller than a predetermined value EX3, it is determined that there is continuity and the process proceeds to step (727); otherwise, the process proceeds to step (728) and returns.

In all of the above embodiments, it was determined whether distance measurement was being performed on the same subject based on the image plane movement speed and the continuity of changes in the image plane position. It is clear that the invention is effective.

In addition, as a completely different determination method, the previous image signal and the image signal obtained in the current distance measurement are compared, and a predictive calculation is performed when it is determined that both image signals are of the same subject. I can do it.

As described above, in the present invention, if it is predictable, NG display is performed when in-focus display is impossible, but in this case,
Even though the image actually observed in the viewfinder is out of focus, an in-focus display will appear.

Therefore, the display method may be different from the conventional focus display to notify the photographer that predictive control is being performed.

In addition, considering the above problems, we will only accept NG if it is unpredictable.
It is also conceivable to display a display and not display an in-focus display during prediction.

Furthermore, it is also possible to notify the photographer of the camera status only by displaying either the predictable or NG display.

〔effect〕

As described above (in the present invention, since the in-focus display is performed based on predictive calculation processing (when it is determined that the lens can be driven), the focus adjustment device based on predictive calculation processing Even if there is an object, it is possible to display the focus.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing a flowchart of "prediction calculation" used in the focus adjustment device according to the present invention, and FIG.
3 is a principle explanatory diagram explaining the operation when the lens is driven in the "predictive calculation" process, and FIG. 3 is based on FIG. 2 (an explanatory diagram for explaining the lens driving state, and FIG. 5 is an explanatory diagram showing a main flowchart for explaining the operation of the focus adjustment device according to the present invention; FIG. 6 is a circuit diagram showing an embodiment of the focus adjustment device; FIG.
FIG. 7 is an explanatory diagram showing a flowchart of the "image signal manual power" subroutine shown in the figure. FIG. 7 is an explanatory diagram showing a flowchart of the "lens drive" subroutine shown in FIG. 5. FIG. FIG. 9 is an explanatory diagram showing a flowchart of the subroutine "continuity determination of image plane position" shown in FIG. 8, and FIG.
FIG. 11 is an explanatory diagram showing a flowchart of the "Continuity determination of image plane position" subroutine. FIG. 11 is an explanatory diagram showing a flowchart of the "Focus detection accuracy determination" subroutine shown in FIG. FIG. 13 is an explanatory diagram showing a flowchart of the subroutine "aptitude determination", and FIG.
FIG. 14 is an explanatory diagram showing a flowchart of the subroutine "Another prediction calculation"; FIG. 15 is an explanatory diagram showing a flowchart of the "prediction/non-prediction determination" subroutine shown in FIG. 14; Figure 16 is the 15th
FIG. 17 is an explanatory diagram showing a flowchart of the subroutine "Judge prediction accuracy" shown in FIG. 15. FIGS. FIG. 2 is an explanatory diagram showing a flowchart of the "continuity determination of image plane position" subroutine of FIG. LED...Light emitting diode PH1...Computer SNS...Sensor device LPR3...Control circuit Patent applicant Canon Co., Ltd.

Claims (1)

[Claims] A focus detection circuit that determines the amount of defocus of the photographic lens;
In the past, several automatic focusing devices have been developed that include a lens drive circuit that drives a lens based on the output of the focus detection circuit, and repeatedly perform an operation of detecting the amount of defocus by the focus detection circuit and a lens drive operation based on the detection result. An arithmetic circuit is provided that calculates the image plane position of the subject after a predetermined time using a several-order function based on the amount of defocus obtained by the focus detection circuit in the second focus detection circuit. In addition to driving the lens to match the positions, a determination circuit is provided to determine whether proper focusing can be obtained by driving the lens to the image plane position determined by the arithmetic circuit, and the determination circuit makes a determination. An automatic focusing device characterized in that when it is determined that proper focusing can be obtained as a result, a proper display is made and the lens is driven to the image plane position determined by the arithmetic circuit.