JPH04218009A - Focus detecting device - Google Patents

Abstract

PURPOSE:To accomplish appropriate and rapid automatic focus detection without receiving the effect of the change of the driving speed of an image-formation optical system by correcting the error of a defocusing quantity caused by driving the imageformation optical system while charge is accumulated. CONSTITUTION:A focus detecting means 104 for detecting the focusing state of a photographing lens 101 transmits the timing of starting and finishing the accumulation of the charge to a control means 109. A signal pulse concerning the moving quantity of the lens 101 is counted by a moving quantity counting means 107 and a lens moving quantity at each time interval is detected to be stored in the memory 110. In the case of changing the speed of the image- formation optical system while the charge is accumulated, the timing of changing the speed is detected and the correction quantity of the error of the defocusing quantity caused by driving the image-formation optical system is changed while the charge is accumulated by depending on relation between the timing of changing the speed and the time of the accumulation of the charge.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus detection device for an optical device such as a camera.

0002

[Background of the Invention] As an automatic focus detection device for a camera, the amount of defocus corresponding to the amount of deviation between the planned focal plane of the objective lens (imaging optical system) and the actual imaging plane of the object is calculated at certain time intervals. However, it is known to perform automatic focus adjustment by driving an objective lens in accordance with this defocus signal. However, when driving the objective lens in accordance with the defocus signal that is output discretely in this way, if the subject is moving in the optical axis direction of the objective lens while the objective lens is being driven, the lens drive described above will not work properly. Since this is done without regard to subject movement, there is a drawback that proper focus adjustment cannot be performed.

0003

[Object of the Invention] The purpose of the present invention is to solve these drawbacks and to obtain a focus detection device capable of properly and quickly detecting a focus without being affected by the drive (speed change) of the imaging optical system. do.

0004

EXAMPLES The contents of the present invention will be explained below based on specific examples. FIG. 1 is a block diagram showing a configuration in which the present invention is applied to a camera. In the figure, a photographing lens 101
The focus detection means 104 for detecting the focus adjustment state of
Focus detection optical means 201 and photoelectric conversion means 20
2. It is composed of a focus detection calculation means 203. The photoelectric conversion means 202 receives a subject image formed by the photographing lens 101 and the focus detection optical means 201, and generates an image output according to the image.

This photoelectric conversion means 202 has a charge accumulation type photoelectric conversion section, and the charge accumulation time can be determined by giving such a function to the photoelectric conversion section itself by devising the device, or by focusing the image output. It may be determined by processing by the detection calculation means 203. In any case, the focus detection means 104 transmits the start and end timings of charge accumulation to the control means 109.

The period from the end of charge accumulation to the start of the next charge accumulation is used for charge transfer and defocus amount calculation. The defocus amount is calculated by a known method and is also transmitted to the control means 109. The time counting means 108 receives the start and end timings of charge accumulation or other timings from the control means 109, counts the time interval of each timing, and the result is stored in the memory 110 by the control means 109.

In FIG. 3, the horizontal axis represents time t, and the vertical axis represents the moving position χ of the lens 101, and the solid lines 301, 3
01' represents the movement trajectory of the lens 101, and the thick solid line 3
02 corresponds to the object movement trajectory when the object moves in the optical axis direction of the imaging lens 101. If the object is stationary, it will be parallel to the time axis, and when there is the above movement, it will be parallel to the time axis as shown in the figure. It has a tendency to

Movement trajectory 301, 301' of lens 101
If substantially coincides with the object movement locus 302 representing the movement of the image plane position based on the movement of the object, the imaging lens 101 is in a focused state. The driving of the imaging lens 101 from the point Q0, where the lens movement trajectory 301 largely deviates from the object movement trajectory 302, to the point Q1, where the lens movement trajectory 301 first almost coincides with the object movement trajectory 302, is called convergence drive. Driving the imaging lens to follow 302 will be referred to as follow-up drive.

[0009] Time tn-1, tn, tn+1, t
n+2 indicates the time point at which charge accumulation of the photoelectric conversion means 202 starts, and time t'n-1, t'n, t'n+1
indicates the end point of charge accumulation, and t'n indicates the point of transition from convergence drive to follow-up drive. Tn-1, Tn
represents charge accumulation time, T nc −1, T nc
is the calculation time, during which time the focus detection calculation control means 203 calculates the defocus amount based on the data from the photoelectric conversion means 202, and the defocus amount and the memory 1
10 and the estimated defocus amounts Xn-1 and Xn, which will be described in detail later, and the correction amount δn-1 for correcting the estimated defocus amount as the target object moves.
(τ) and δn (τ) are calculated, respectively.

[0010] This estimated defocus amount is at time tn-1
, tn, tn+1, and tn+2 in the defocus amount counting means 106. T'n is time t
'n to time t'n, Mn-1
, Mn represent the amount of movement of the lens 101 including the direction during times Tn-1 and Tn, respectively; for example, Mn
are the position of the lens 101 at time tn and time t'n
This is the amount representing the distance from the position of the lens 101 at , including the direction.

Therefore, when the lens 101 moves in one direction and when it moves in the opposite direction, the signs of Mn-1 and Mn are reversed. M nc −1 and M nc are respectively T nc
−1, T nc represents the amount by which the lens 101 has moved, including the direction. In this embodiment, the image plane position at a predetermined timing is determined, and based on this, the movement of the image plane due to the movement of the object is corrected, and the lens 101 is driven. A method for calculating the amount related to the movement of the target object (subject) will be described later, but the amount of correction for the movement of the image plane due to the movement of the object is expressed as δ(τ) as a function of time τ.

Furthermore, the estimated defocus amount is determined at the end of the calculation as described above, but at this time, time has already passed since the photoelectric conversion. As will be described later, the image plane position at the center of the charge accumulation time is corrected by the amount of movement of the image plane position due to object movement during the elapsed time (the calculation method will be explained later). .

[0013] In this way, the estimated defocus amount itself is the predicted amount, but by taking into account the above-mentioned δ(τ), the estimated defocus amount becomes the image after τ has elapsed from the end of the calculation. surface position can be predicted. In FIG. 3, the estimated defocus amount Xn-1 is set in the defocus amount counting means 106 at a time tn-1.
In this case, a point separated by an estimated defocus amount Xn-1 from the current position Q0 of the lens 101 is defined as Q2. This point Q2 is the predicted image plane position at the timing tn-1 of the end of the calculation. This point Q2
A correction straight line 310 (
Indicated by a dashed line. ), the distance between the horizontal line from point Q2 and this correction straight line 310 at each time point tn-1 +τ represents the correction amount δn-1 (τ).

The same is true for the correction amount δn (τ), and from the lens position Q2 at time tn and the estimated defocus amount Xn at this time, point Q4 is the predicted image plane position at time tn. A correction straight line 311 is drawn approximately parallel to the object movement trajectory 302 from this point Q4. Referring again to FIG. 1, the control means 109 changes the time point tn-1 +
δn so that the correction amount at τ is δn-1 (τ)
A subject movement correction pulse having a frequency corresponding to -1 (τ) is sent to the defocus amount counting means 106, and the value of the estimated defocus amount is corrected to track the movement of the subject.

In this way, the defocus amount counting means 1
06 holds the estimated defocus amount at each moment, taking into account the movement of the subject, and the drive signal generating means 1
05 responds to the contents of the defocus amount counting means 106,
Depending on whether the content is a positive value, a negative value, or zero, a signal is generated that causes the drive motor of the lens 101 to rotate forward, reverse, or stop, respectively.

A driving means 102 including the driving motor described above drives the lens 101 in response to this signal. The movement amount signal generating means 103 generates pulses as the lens 101 moves. As a method, Japanese Patent Application Laid-Open No. 58-88710
An independent means may be provided as described above, or if the drive motor is a pulse motor, a drive pulse may be used instead.

The signal pulses related to the amount of lens movement are counted by the movement amount counting means 107, and the counted value becomes zero after being read in accordance with the timing of the start tn-1 and end tn-1' of charge accumulation. will be reset. In this way, the lens movement amounts Mn-1 and Mnc-1 at each time interval are detected by the movement amount counting means 107 and stored in the memory 110.

Since the drive signal generating means 105 drives the lens in the direction of zeroing the contents of the defocus amount counting means 106 based on the contents of the defocus amount counting means 106, the defocus amount counting means 106 The estimated defocus amount in the defocus amount counting means 106 is counted up or down in the direction of approaching zero by a signal pulse related to the lens movement amount from the movement amount signal generating means 103 that is input to the defocus amount counting means 106 .

In this way, the defocus amount counting means 1
As the lens moves, the estimated defocus amount held by 06 gradually decreases and approaches zero, and the system approaches the in-focus state. In the case of FIG. 3, such convergence drive continues from tn-1 to tn. However, charge accumulation time Tn-1
Although it is preferable that the lens moves at a constant speed during the period corresponding to , it is not necessarily necessary that the lens moves at a constant speed during the period corresponding to the transfer/calculation time Tn-1 C . For example, it may be stopped during the charge transfer time.

Next, the next cycle starting from time tn will be explained. At time tn, period Tn-1
The amount of defocus based on the data received in the period Tn-1C has already been calculated by the focus detection means 104. Using this defocus amount and the contents stored in the memory 110, a new estimated defocus amount Xn and a correction amount δ
n (τ) is calculated.

At the calculated time tn, the new estimated defocus amount Xn is set in the defocus amount counting means 106, and at the same time, charge accumulation in the photoelectric conversion means 202 is restarted. δn(τ
), the estimated defocus amount is corrected as described above. As for lens driving, convergence driving similar to the previous time is performed until time t''n. Time t''n
Then, the focus state is reached, and the estimated defocus amount in the defocus amount counting means 106 becomes exactly equal to zero. As a result, the drive signal generation means 106 transmits a signal to stop the drive to the drive means 102, and the lens 101 stops. Since no movement amount signal is generated in this stopped state, the estimated defocus amount held by the defocus amount counting means 106 also remains at zero for a short time.

However, when the subject is moving, the control means 109 generates subject movement correction pulses at a frequency corresponding to the correction amount δn (τ). This pulse is δn
The defocus amount counting means 106 counts up or down depending on whether (τ) is positive or negative.

Therefore, the estimated defocus amount, which is the content of the defocus amount counting means 106, is no longer zero. As a result, a lens drive signal is generated from the drive signal generating means 105 to move the lens, a lens movement amount signal is generated, and the estimated defocus amount of the defocus amount counting means 106 becomes zero again. After a while, when the in-focus state begins to deteriorate due to the movement of the subject, the subject movement correction pulse is generated again, and the same thing occurs at least until the end of charge accumulation t'n.
It can be continued until Of course, it is preferable to continue until time tn+1. During this period, the lens is driven along the correction amount δn (τ) due to the movement of the subject as shown in FIG. 3, so it is a period of follow-up driving.

During this follow-up drive, the lens also maintains the correction amount δn.
Since it moves along the straight line 311 shown by the broken line representing (τ), there may be many small movements and stops, but on average it moves at a nearly uniform speed. Therefore, even if the subject moves based on the predictive calculation, the lens will be able to adjust its focus appropriately. Next, using Figure 4,
A method for calculating the estimated defocus amount X(o) and the correction amount δn(τ) will be described in detail. FIG. 4 is an enlarged view of a part of FIG. 3. In the case where the lens drive speed is constant during the accumulation time, such as during the Tn-1 period, it becomes a little simpler, but in Fig. 4, it is the most complicated case, that is, when the lens drive speed changes during the accumulation time, and it is actually attempts to analyze cases where unavoidable errors are included.

From the data up to time tn, the estimated defocus amount Xn at time tn and the correction amount δn (τ) that changes over time reflecting the movement of the subject are as shown in the figure. Here, if the estimated defocus amount Xn is completely correct, then
The tip of n should be on the thick solid line 302, but generally an error Δ is included, as shown in the figure. Generally, this error Δ is relatively large when the imaging lens 101 is far away from the in-focus position, but becomes smaller as it approaches the in-focus position. In the state shown in FIG. 4, the lens 101 is quite close to the in-focus position, so the error Δ is a very small value so that it can be considered that the lens 101 is substantially in focus at point Q1 on the lens movement trajectory 301. It becomes.

The moving trajectory of the lens 101 progresses toward the broken line 310 of the estimated trajectory determined from the estimated defocus amount Xn and the correction amount δn (τ) as shown by the solid line 301 (convergence drive).
After matching at point Q1, it moves along the estimated trajectory (follow-up drive). Furthermore, in FIG. 4, mn, m'n, and mn+1 indicate the positions of the lens 101 at time points tn, t'n, and tn+1. Also, the direction from the point where the straight line l connecting the tip Q4 of Xn and the midpoint (tn + Tn /2, χn) of the charge accumulation time in the thick solid line 302 intersects with the time axis of the accumulation end time t'n to m'n is The size including X'n as shown in the diagram
Let Zn+1 be the size including the direction from the coordinates χn of this midpoint to mn+1 as shown in the figure.

When the situation during the charge accumulation time is like this, the focus detection means 10 detects the image output at this time.
If the defocus amount calculated by 4 is Pn+1, the following relationship exists.

[0028]

[Math 1]

Note that Pn+1 is the focus detection calculation means 203
, T'n and Tn are the outputs of the time counting means 108
As the outputs, M nc and Mn are the movement amount counting means 1
As the output of 07, Xn is obtained as the result of the previous calculation, and these are stored in the memory 110. Various methods are possible to calculate the correction amount δn+1 (τ) due to the movement of the subject. For example, this may be determined by connecting the position indicated by the previous estimated defocus amount and the current estimated defocus amount.

However, in this case, there is a drawback that the error Δ is calculated each time. FIG. 5 is the same as FIG. 3 and shows only the parts necessary for explanation. In order to obtain the correction amount δn+1 (τ), it is preferable to use the coordinates χn, χn-1, χn-2, . . . on the thick solid line at the center of the past charge accumulation times Tn-1, Tn. When dTn and ΔTn are determined as shown in Figure 5, each
dTn =T nc -1+1/2(Tn-1 +T
n ), ΔTn = T nc + 1/2Tn Therefore, the tilt kn+1 (image plane movement speed) is kn+1 = (
From χn −χn-1 )/dTn

[0031]

[Math 2]

Using this, the estimated defocus amount Xn+1
, the correction amount δn+1 (τ) is

[0033]

[Math 3]

[0034] If the subject is stationary or cannot be determined, the estimated defocus amount Xn at time tn+1 is assumed to be stationary.
+1, and the correction amount δn+1 (τ) is determined as follows.

[0035]

[Math 4]

[0036] The slope k is further calculated from the past several slopes kn and k
n-1, kn+2... may be obtained by weighted averaging, or the coordinates χn, χn-1,
A curve of an appropriate degree, for example, a quadratic curve, which best fits the curve may be obtained from χn-2, and the next slope kn+1 may be interpolated. Alternatively, kn+1 obtained in this way may be followed with a slope of αkn+1 using a constant satisfying 1>α>0.

The control means 109 controls the lens as indicated by the broken line 3 in FIG.
Pulses are sent to the defocus amount counting means 106 at time intervals determined from the above-mentioned slope kn+1 so that the defocus amount counting means 106 is driven to follow along the angle kn+1. Specifically, the image plane movement speed |kn
The larger +1| is, the shorter the time interval is to send out pulses, but it is better to send out the pulses somewhat in advance so that the movement of the lens does not follow the broken line 311 in FIG.

In addition, in the above explanation, for simplicity, we have taken into consideration the case where all the groups are fixed and moved as the lens 101 whose focus is detected, but even when focusing is carried out by moving only one group,
A single lens equivalent to the entire group is considered, and the movement of the single lens is treated as corresponding to the movement of the lens 101. Furthermore, blocks 105, 106, 10 in FIG.
7, 108, 109, 110 and block 203 of FIG.
can be configured in whole or in part by a microcomputer.

Next, the overall time flow will be explained using a flowchart. In Figure 6, step 1 operation starts (STA
RT), in step 2, two types of interrupts to be described later are disabled and the parameter Vint is set to zero. In step 3, Xp corresponding to the estimated defocus amount Xo and a pulse interval Tp that determines the correction amount δ0 (τ) are determined. Initially, focus is detected without moving the lens, so Xp = 0,
Let Tp = 0. However, when the value of Tp is other than zero, it indicates the pulse interval at which the control means 109 sends the object movement correction pulse to the defocus amount counting means 106, but Tp=0 means that no pulse is generated. shall be.

Further, the defocus amount counting means 106 is Tp
It is assumed that the count contents are up-counted and down-counted by the pulses received in response to >0 and Tp <0, respectively. In step 4, the contents of the movement amount counting means 107 are set to zero to prepare for the start of counting. In step 5, the value of Xp is set in the counter of the defocus amount counting means 106. When Xp≠0, the drive signal generating means 105 generates a signal from the lens 10 via the drive means 102 according to the polarity, that is, the sign of Xp.
1 forward or backward.

In this case, since Xp=0, the lens 101 is stationary. In step 6, the value Tp is set in the counter of the control means 109 in order to generate a subject movement correction pulse. This counter is counted down at a predetermined speed, and when the contents of the counter become zero, the control means 10
9 sends one pulse to the defocus amount counting means 106.

The contents of the counter are again set to the value of Tp. In this way, a pulse is generated every time interval Tp. Further, an instruction for up-counting or down-counting is also transmitted to the defocus amount counting means 106 depending on the polarity of Tp. In this way, the value of Tp is repeatedly set in the counter, but the movement of the lens is δn
The first pulse may be generated at an appropriate time shorter than Tp so as not to follow the straight line of (τ).

For example, the first value set in the counter is set to 0.5Tp. Here, the value of Tp is given by Tp = q/kn for kn in Equation 5, where q is determined by the discount speed of the counter and how much movement of the lens 101 the movement amount signal generating means 103 generates with one pulse. This is a constant determined by whether or not it occurs.

Next, in step 7, the counter of the time counting means 108 is zeroed to start counting, and at the same time, in step 8, charge accumulation is started. Then step 9 and 10
allows speed change interrupts and charge accumulation end interrupts. When the system is Tn in FIG. 3, a speed change interrupt occurs at time t'n. For this reason, the speed change interrupt, for example,
This is generated when the content of the defocus amount counting means 106 changes from non-zero to zero. This jumps to the speed change interrupt generation routine shown in FIG. Next, in step 12, subsequent speed change interrupts are prohibited, and in step 13, the time counting means 1 is
The contents of the counter 08 are stored in T'n.

Next, the parameter Vint indicating that a speed change interrupt has occurred is set to 1, and the process is returned. Thereafter, an interrupt indicating the end of charge accumulation occurs and the process moves to FIG. First, in step 17, speed change interrupts are prohibited, and in step 18, the contents of the counter of the time counting means 108 are set to Tn.
to be memorized. This value corresponds to the charge accumulation time. after that,
This counter is set to zero.

When there is a speed change interrupt, T' in FIG.
It is necessary to calculate the amount corresponding to n, ie, the time from the occurrence of the speed change interrupt to the end of charge accumulation, and this is done in steps 19, 20, and 22. In step 21, the contents of the movement amount counting means 107 are read, and Mn is stored as the movement amount of the lens 101 during this period. Then, the counter contents are set to zero again.

In step 23, the photoelectric conversion means 202 of FIG.
The data is transferred to the focus detection calculation means 203, and the focus detection calculation control means 203 performs calculation to obtain defocus Pn+1. At the same time as step 23 ends, step 24
The lens drive is stopped at Steps 25 and 26, and the time Tnc and lens movement amount M required for data transfer and calculation are calculated at Steps 25 and 26.
Calculate nc.

[0048] In step 27, these Xn, Tn,
T'n, Tnc, Mn, Mnc, Pn+1
The estimated defocus amount Xn+1 and the correction slope kn+1 are calculated using Equations 4, 5, 6, and 7. In step 28, these values are converted into the actual number of drive pulses Xp and pulse interval Tp, and in step 30, the process returns to A to start the next charge accumulation cycle. From then on, this process will be repeated.

[0049]

According to the present invention, when the speed of the imaging optical system is changed during charge accumulation in the photoelectric conversion means, the timing of the speed change is detected, and the timing of the speed change and the charge accumulation are determined. Since the correction amount of the error in the defocus amount caused by the driving of the imaging optical system is changed during the charge accumulation or during the calculation of the calculation means, depending on the relationship with the time, the image formation Appropriate and rapid automatic focus detection is possible without being affected by the drive (speed change) of the optical system.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention;

FIG. 2 is a block diagram showing a configuration example of the focus detection means in FIG. 1;

[Fig. 3] Fig. 3 is a graph showing the relationship between the movement of the imaging lens and the movement of the target object;

[Fig. 4] Fig. 4 is a graph that enlarges a part of Fig. 3;

[Figure 5]
FIG. 5 is a graph for determining the correction amount δ(τ),

[Figure 6]
FIG. 6 Flowchart for explaining the operation of this embodiment,

FIG. 7 is a flowchart for explaining the operation of the present embodiment;

FIG. 8 is a flowchart for explaining the operation of this embodiment.

[Explanation of symbols of main parts]

101... Photography lens 102...Driving means 103...Movement amount signal generation means 104... Focus detection means 106...Defocus amount counting means

Claims (1)

[Claims] 1. charge accumulation type photoelectric conversion means for photoelectrically converting a light image of the target object that has passed through the imaging optical system; and an image forming plane of the target object and a predetermined focal plane of the imaging optical system based on the output of the photoelectric conversion means. In the focus detection device, the focus detection device has a calculation means for calculating a defocus amount representing a deviation of the image forming apparatus, and a drive means for driving the imaging optical system based on the output of the calculation means, when the focus detection device When the speed of the imaging optical system is changed, the timing of the speed change is detected, and depending on the relationship between the timing of the speed change and the time of the charge accumulation, the control is performed during the charge accumulation or during the calculation of the calculation means. A focus detection device comprising: a correction means for changing a correction amount of an error in the defocus amount caused by driving the imaging optical system.