JPH09230228A - Predictive focusing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a predictive focusing device capable of stabilizing follow-up operation to the focus position of an object by previously accurately judging whether the object stands still or is moving. SOLUTION: Defocusing amount is calculated from range-finding data. In the case the difference of the calculated value from the previous defocusing amount is equal to or below a specified value, that is, <=250μm; whether the difference between the defocusing amount one second before and the defocusing amount at this time is >=250μm or not a specified time, that is, one second after. In the case it is <=250μm, the subject is judged as a still body, and the number of driving pulses is calculated. By judging in such a way, whether the subject is the still body or a moving body is accurately judged and the stable follow-up characteristic is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention determines the predicted image velocity of an image plane of a subject and the amount of focus shift, determines the drive speed of the focus adjusting member from these data, and controls the speed of the focus adjusting member. The present invention relates to a predictive focusing device that considers further smoothing the followability of predictive focusing by accurately determining whether a subject is stationary or moving in the predictive focusing device that performs focusing.

[0002]

2. Description of the Related Art The applicant of the present invention repeatedly measures a distance to an object by a distance measuring optical system, calculates a moving speed of an image from distance measuring data and a distance measuring cycle time which are continuously obtained,
The predicted image speed of the image is calculated from the previous image speed and the current image speed, and the focus adjustment is performed by determining the predicted image speed of the image plane and the drive speed of the focus adjustment member that takes the current defocus amount into consideration. A focusing device (Japanese Patent Application No. 4-26245) was proposed. With this proposal, it was possible to simplify the calculation, improve the responsiveness of focusing, and improve the excessive control. If this device operates in an ideal manner, it can accurately follow the image movement of the object, but in reality, the focus information (distance to the object) obtained by the distance measuring operation includes an error. .

[0003]

By the way, the image speed of the object is actually very slow even if the moving speed of the object is high, and the image information is stationary due to the error of the focus information measured by the normal distance measurement cycle. It is difficult to determine whether they are moving or moving. Therefore, if the distance measurement results are simply compared and determined, a stationary object is determined to be a moving object due to the influence of the distance measurement error. Further, if the judgment is made strict, there may be a case where the moving body prediction is not applied at all.
In this way, if the stationary body or the moving body is mistaken, the processing method is different, so that the focus adjustment member is inadvertently driven due to an incorrect determination, and smooth followability cannot be ensured.
An object of the present invention is to provide a predictive focusing device capable of stabilizing the follow-up operation with respect to the focus position of the subject by accurately determining in advance whether the subject is stationary or moving. .

[0004]

In order to achieve the above object, a predictive focusing apparatus according to the present invention calculates a rate of change in image speed from a moving speed of an image plane of a subject which is continuously obtained to calculate the predicted image speed. And the focus shift amount thereof, the drive speed of the focus adjusting member is determined from these data, and in the predictive focusing device that performs focus by controlling the speed of the focus adjusting member, measurement of continuously obtained objects is performed. Determining means for determining whether the object is a moving object or a stationary object from the distance data is provided, and the determining means determines the defocus amount of the focus adjusting member with respect to the image position of the previously measured object and the image position of the object measured this time. Difference of the defocus amount of the focus adjusting member is smaller than a predetermined value, and the diff of the focus adjusting member with respect to the image position of the subject measured after the elapse of a fixed time and immediately before the elapse of the fixed time. When the difference between the defocus amounts of the focus adjusting member relative to carcass weight and image position of this distance measurement subject is smaller than the predetermined value, it is constituted to determine that the subject is stationary body. Further, in the above configuration, when the defocus amount changes by the predetermined value or more before the elapse of the predetermined time, it is determined that the subject is a moving body.

[0005]

According to the above configuration, it is determined whether the object is stationary or moving,
In particular, it is possible to accurately determine that a subject having a slow moving speed is a moving body without making a mistake, and smoothly follow the focus position of the subject.

[0006]

Embodiments of the present invention will be described below in more detail with reference to the drawings. FIG. 1 is a view showing an embodiment of a back focus control type auto focus camera equipped with a predictive focusing device according to the present invention, and shows only a portion directly related to the present invention. The taking lens 3 is mounted on a mount portion of a fixed body (not shown).
The fixed body is composed of the taking lens 3, the external appearance of the camera, the back cover, and the like. The movable body 11 includes a mirror box, a finder mechanism, an AF distance measuring system, an exposure device, a film opening (film surface), a film feeding system, and the like. The movable body 11 is built in a fixed body, and is supported by a guide rail so as to be slidable in the optical axis direction.

The focus adjusting member corresponds to a portion including the body driving device 5 and the movable body 11 in this example. Also,
The AF distance measuring system is composed of an AF sensor 8 and a distance measuring device 1. The movable body 11 is moved in the optical axis direction by AF control, and the film surface 10 thereof is brought to the focal plane. Reflected light of a subject (not shown) is input to the AF sensor 8 via the taking lens 3. The distance measuring device 1 measures the distance based on the output of the AF sensor 8 and sends the electric signal to the control device 2. The distance measuring device 1 detects the distance by the phase difference method, and the distance measurement is continuously and repeatedly performed.

The control device 2 obtains the distance measurement result from the distance measurement device 1 and performs calculation to calculate the defocus amount, and calculates the moving speed of the image from the continuously obtained defocus amount and the distance measurement cycle. To do. Then, the next image velocity is predicted and calculated from the image velocity obtained continuously. From the current defocus amount and the predicted image speed, the drive speed of the body (the drive speed of the film surface) such that the focus shift becomes zero after one distance measurement cycle is calculated. The control device 2 outputs a drive signal to the body drive device 5 and drives at the calculated body drive speed. Then, the actual drive position of the body is monitored by an encoder or the like. Further, these are stored in the memory circuit 4. The memory circuit 4 stores the distance measurement data processed by the control device 2 and the drive amount data, and the stored data is used when the control device 2 calculates.

FIG. 2 is a diagram for explaining the operation of the predictive focusing device according to the present invention, and is a diagram showing an example of a process of causing the film surface to follow the locus of image movement. The vertical axis represents the image position of the subject from the infinite position to the closest position, and the horizontal axis represents the time axis. A shows the image plane locus of the subject, and B shows the drive locus of the film surface of the movable body, and the defocus amount of the image plane position between them is DF ₁ to.
They are represented by DF ₅ , DF ₁ ′ to DF ₄ ′, respectively.
Further, ΔT _n represents the distance measurement cycle time, which is the time from the last distance measurement time (accumulation center time) to the current distance measurement time or the time from the last calculation end to the current calculation end.

The control device 2 first calculates the image velocity of the subject from the result of repeated distance measurement performed by the distance measuring device 1. After that, if the processing shown in FIG. 3 is performed and it is determined that the object is a moving object, the defocus amount DF _{n-1 of} the image plane position obtained from the previous distance measurement result and the defocus amount of the current distance measurement result. The amount of movement of the subject is obtained by comparing DF _n . The image speed V _n of the subject is calculated by dividing this by the AF cycle time ΔT _n from the time of the last distance measurement to the time of the current distance measurement. _{V n = (DF n-1} -DF n + ΔP n) / ΔT n ··· (1) ΔP n; calculating a predicted image rate than the driving amount more previous and current image speed of the movable body between the distance measurement.
Assuming that the predicted image speed is V _{n + 1} , the current moving speed is V _n , and the previous moving speed is V _n-1 , the predicted image speed can be calculated by the equation (2).

V _{n + 1} = V _n × (V _n / V _n-1 ) ... (2) V _n / V _n-1 ; image velocity change rate The control device 2 determines the predicted image velocity of these objects and Using the current data of the defocus amount, find the drive speed VB _n of the movable body (film surface) so that the defocus amount becomes 0 by the end of the next distance measurement cycle. VB _n = V _{n + 1} + DF _n ′ / ΔT _n (3) DF _n ′; current assumed defocus amount = DF _n + (V
_n −VB _n−1 ) · ΔT _n Here, when only one image velocity is obtained, the drive velocity VB _n 'of the movable body is calculated by the equation (4) based on this velocity and the defocus amount.
To determine. VB _n '= V _n + DF _n ' / ΔT _n (4) While the movable body is being driven at the drive speed calculated from the predicted image speed and defocus amount, the time during which the movable body is driven at this speed is the previous AF cycle. When it is equal to the time, it is considered that the film surface of the movable body has caught up with the focus position of the image of the subject, and at that time, the driving excluding the term of DF _n '/ ΔT _n from the expressions (3) and (4). Switch to speed and continue speed control.

FIG. 3 is a diagram for explaining the operation of the predictive focusing device according to the present invention, and is a flow chart for judging the stationary body or the moving body of the subject. In the description of FIG. 2, the control device 2 obtains the distance measurement result from the distance measurement device 1 and performs calculation to calculate the defocus amount, and before performing the process for predictive focusing, the control device 2 moves the moving object or the stationary object. Make a decision. The control device 2 is
When the current defocus amount is calculated, the difference between the previous defocus amount and the current defocus amount is calculated. And
It is determined whether or not the amount of movement of the image plane is a predetermined value or more, 250 μm or more in this example (S301). If the object is moving for 250 μm or more, it is determined that the object is a moving object, and the image velocity calculation, the predicted image velocity calculation, and the drive velocity calculation are performed as described above (S307,
S308, S309).

If it has not moved for 250 μm or more, it is next determined whether or not a predetermined time, that is, one second or more has elapsed from this determination (S302). The time of 1 second is sufficient to make a reliable judgment even when it is difficult to judge whether the subject is moving slowly and is a moving body or a stationary body. While one second has not elapsed, the difference between the current defocus amount and the current defocus amount in S301 is determined, and if 250 μm is moved, it is determined that the object is a moving object, and the process proceeds to S307. 25
If it does not move by 0 μm or more, it is determined to be a stationary body at this moment. When 1 second has elapsed, the counting for 1 second is restarted. Then, it is determined whether or not the difference between the defocus amount one second before and the current defocus amount is 250 μm or more (S303, S304). If the thickness is 250 μm or more, the process proceeds to S307. In the case of 250 μm or less, since there is no movement of 250 μm or more for 1 second or more, it is determined that the object is a stationary body, and the process proceeds to drive pulse number calculation (S306).

FIG. 4 is a diagram showing the followability of the body (film surface) when the subject is stationary, and it is when the moving body or the stationary body is not judged. This example shows a focal length of 300
A lens of mm is used. Even when the image position is stationary, the film surface follows the stationary position while moving slightly. Since the follow-up is within the permissible range D, the focus does not deviate, but the position of the film surface is always unstable in movement. FIG. 5 is a diagram showing the followability of the body (film surface) when the subject is stationary. Control is performed to accurately determine whether the object is a moving body or a stationary body, and to stop the driving of the film surface in the case of a stationary body. This is the case. In the present invention, since the moving body and the moving body can be accurately determined, the driving of the film surface can be stopped to eliminate unnecessary movements and the follow-up operation can be stabilized.

[0015]

As described above, according to the present invention, the predicted image velocity and its focus shift amount are calculated by calculating the rate of change of the image velocity from the moving velocity of the image plane of the subject which is continuously obtained. In the predictive focusing device that determines the driving speed of the focus adjusting member from the data and performs focus control by controlling the speed of the focus adjusting member, whether the object is a moving object or a stationary object from continuously measured object distance measurement data. The determination means is provided to determine the difference between the defocus amount of the focus adjustment member with respect to the image position of the subject measured last time and the defocus amount of the focus adjustment member with respect to the image position of the subject measured this time by a predetermined value. A smaller defocus amount of the focus adjustment member for the image position of the object measured immediately before the elapse of a certain time after the elapse of a certain time and the focus adjustment member for the image position of the object measured this time. When the difference between the focus amount is smaller than a predetermined value is to determine the subject is stationary body. Therefore, even when the vehicle is moving at a slow speed that is buried in the distance measurement error, it can be detected as surely moving, and stable tracking characteristics of the moving object predicting operation can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a back focus control type auto focus camera equipped with a predictive focusing device according to the present invention, and shows only a portion directly related to the present invention.

FIG. 2 is a diagram for explaining a focusing operation by the predictive focusing device according to the present invention, and is a diagram showing an example of a process of causing the film surface to follow the locus of image movement.

FIG. 3 is a diagram for explaining the operation of the predictive focusing device according to the present invention, and is a flowchart for determining a stationary body or a moving body of a subject.

FIG. 4 is a diagram showing the followability of a body (film surface) when a subject is stationary, which is a case where a moving body or a stationary body is not judged.

FIG. 5 is a diagram showing the followability of a body (film surface) when a subject is stationary, and is a case where it is determined to be a stationary body after a certain period of time has elapsed.

[Explanation of symbols]

 1 ... Distance measuring device 2 ... Control device 3 ... Photographing lens 4 ... Memory circuit 5 ... Body drive device 7 ... Release button 8 ... AF sensor 11 ... Movable body

Claims (2)

[Claims] 1. A predictive image velocity and a focus shift amount thereof are calculated by calculating a rate of change in image velocity from a moving velocity of an image plane of a subject which is continuously obtained, and a driving velocity of a focus adjusting member is determined from these data. In the predictive focusing device that performs focusing by controlling the speed of the focus adjusting member, a determination unit that determines whether the object is a moving object or a stationary object from continuously obtained object distance measurement data is provided. The determination means is configured such that the difference between the defocus amount of the focus adjusting member with respect to the image position of the subject measured last time and the defocus amount of the focus adjusting member with respect to the image position of the subject measured this time is smaller than a predetermined value and is constant. After the passage of time,
When the difference between the defocus amount of the focus adjusting member with respect to the image position of the subject measured immediately before the elapse of the certain time and the defocus amount of the focus adjusting member with respect to the image position of the subject measured this time is smaller than a predetermined value, the subject Is a predictive focusing device characterized by determining that is a stationary body. 2. The predictive focusing apparatus according to claim 1, wherein when the defocus amount changes by the predetermined value or more before the lapse of the predetermined time, the subject is determined to be a moving body.