JP3454631B2 - Predictive focusing device - Google Patents

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 further improves the followability of the predictive focusing, in the predictive focusing device that performs the 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. He proposed a focusing device (Japanese Patent Application No. 4-26245). With this proposal, it was possible to simplify the calculation, improve the responsiveness of focusing, and improve the excessive control. This device can accurately follow the movement of the image of the subject if it operates as ideal, but in reality, the focus information (distance to the subject) obtained by the distance measuring operation includes an error. .

[0003]

This error occurs due to various factors, but in the phase difference type distance measuring device, the error becomes larger as the subject has lower contrast and lower brightness. When this error is large, if the drive speed of the focus adjusting member is determined as it is, the drive speed becomes abnormal and the actual movement of the object is not followed. The object of the present invention is to
SUMMARY OF THE INVENTION It is an object of the present invention to provide a predictive focusing device which solves the above-mentioned problems and which suppresses an abnormal speed due to a distance measurement error and makes the followability of an in-focus position with respect to a subject smoother than in the conventional case.

[0004]

In order to achieve the above object, the predictive focusing apparatus according to the present invention calculates the ratio of the previous and present image velocities from the moving velocities of the image planes of the subject which are continuously obtained. In the predictive focusing apparatus that determines the predicted image speed and the amount of focus deviation, determines the drive speed of the focus adjusting member from these data, and performs focusing by speed controlling the focus adjusting member, the ratio of the image speeds And an upper limit is set for the focusing speed by controlling the speed of the focus adjusting member to a driving speed obtained by multiplying the determined driving speed by a coefficient of 1.0 or less.
It is configured so that it can follow the position . For example,
The coefficient is set to approximately 0.5. The upper limit of the image velocity ratio is determined based on the focal length of the lens, the predicted image velocity detection cycle, and the image velocity.

[0005]

By multiplying the driving speed determined as described above by a coefficient of 1.0 or less, it is possible to suppress an abnormal driving speed caused by a distance measurement error. It is effective that the value of the coefficient is set to a small value when the image plane speed of the subject is very slow, and is brought close to 1.0 as the image plane speed increases. This is because the influence of the error becomes very large when the image plane velocity is slow. Further, when a certain subject is being followed, when another object unexpectedly passes by in front of the object, the reaction of the drive is slowed down by suppressing the drive speed, and a large defocusing is less likely to occur.

Further, by setting an upper limit on the rate of change of the image velocity, it is possible to suppress an abnormal velocity similarly caused by a distance measurement error. The change in image velocity is determined based on the focal length of the lens, the predicted image velocity detection cycle, and the image velocity, and eliminates a velocity change rate that is practically impossible in this apparatus.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described 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 drive 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 the body drive device 5 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 illustrates the operation of the predictive focusing device according to the present invention.
In the figure for explaining the
It is a figure which shows an example of the process which is followed. The vertical axis is the subject
The image position from the infinite position to the closest position, and the horizontal axis is the time axis.
Represents each. A is the image plane trajectory of the subject, B is movable
The drive trajectory of the film surface of the body is shown respectively.
And the defocus amount of the image plane position between them is DF₁~
DF_Five, DF ₁’～ DF_Four’, Respectively.
Also, ΔT_nRepresents the distance measurement cycle time,
Time from distance measurement time (accumulation center time) to current distance measurement time
Interval or time from the end of the previous calculation to the end of this calculation
Is.

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. Calculating the moving amount of the subject by comparing the defocus amount DF _n of this distance measurement result with the defocus amount DF _n-1 of the image plane position obtained from the previous measurement result. 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 ; The image velocity change rate control device 2 determines the predicted image velocity of these objects and Using the current data of the defocus amount, the drive speed VB _n of the movable body (film surface) is calculated 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 decide. 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.

In addition to the control by the above algorithm, the following equations and conditions are added for control. (In the case of follow-up drive) Calculation of predicted image velocity The predicted image velocity is expressed by the equation (2) and the image velocity change rate (V _n /
The maximum value of V _n-1 ) is 2.0. Therefore, even if a value of 2.0 or more is calculated, it is calculated as 2.0. Sign reversal of image velocity When the sign of the image velocity is reversed, it is considered that the moving direction is reversed, so the drive speed is calculated at the current image velocity.

The equation (3) for calculating the movable body driving speed is an equation multiplied by a coefficient C, that is, VB _n = V
_It is calculated as _{n + 1} + DF _n '/ ΔT _n × C. The value of C is 0.5. However, if all of the previous time, current time, and prediction are 1.0 mm / s or more, C = 1.0. When the driving speed is calculated to be equal to or higher than the predetermined maximum driving speed, the driving speed = the maximum driving speed. When the drive speed is calculated to be equal to or less than the predetermined minimum drive speed, when the current defocus amount ≦ focus width, and when the image position is currently exceeded, the drive is stopped, When the current image position is not exceeded, the drive speed is set to the minimum drive speed. When the driving direction is reversed, driving is stopped. Drive after waiting for the next distance measurement result.

(When the release is on (except during continuous shooting)) The same as the one follow-up drive in the case of the follow-up drive, but ΔT _n is calculated not by the distance measurement cycle but by the release time lag. (When the release is ON (during continuous shooting)) At the movable body drive speed VB _n = V _{n + 1} + DF _n '/ ΔT _n × C,
It is calculated as C = 1, and ΔT _n is calculated not by the distance measurement cycle but by the release time lag. Other items are the same as the case of the follow-up drive.

FIG. 3 is a diagram for explaining a method of setting the upper limit value of the image velocity change rate, and is a graph showing the relationship of the image velocity (mm / S) to the subject distance (m) with the subject velocity as a parameter. is there. In this example, the speed of the subject is 1, 4, 10, 20, 40, 100, 200 km / h, respectively.
In the case of h, the image velocity of a subject distance of 0 to 800 m obtained by a camera equipped with a 300 mm telephoto lens is shown. Image velocities in the range of 0.01 to 10 mm / s are listed. For example, the speed of the subject is 100 km / h
When the subject distance is 50 m, the image velocity is 1.0
mm / s. Approaching at this speed, the subject distance is 36m
When the position reaches (the amount of movement is 14 m), the image velocity is 2.
The image velocity is 0 mm / s, and the rate of change in image velocity (V _n / V _n-1 ) is 2.0.

In the above situation, for example, if the photographer is 100 km / h
Distance of a car approaching at 50m is measured 3m further
This means that the shutter is released based on the data measured 6 meters before, and it is almost unthinkable to shoot in such a situation as a real problem. Under the above circumstances, for example, 300
When the distance is measured every ms, the distance is moved by 8.3 m before the next distance measurement, and the rate of change of the image velocity (V _n /
V _n-1 ) becomes 1.2. Therefore, even when shooting under the above conditions, the rate of change in image velocity (V _n / V _n-1 ) is about 1.2, and if the upper limit value of 2.0 is set, most shooting conditions And there is almost no room for error. From the above consideration, it is considered that the error is the cause when the rate of change (V _n / V _n-1 ) in the image velocity exceeds 2.0.

FIGS. 4 and 5 use a lens having a focal length of 300 mm, and the image plane with respect to time when the subject approaches at 100 km / h (subject distance of 100 m at the start) and away (subject distance of 50 m at the start). FIG. 6 is a diagram showing the locus of FIG. 4 and is an example of the case where the movement of the body (film surface) ideally follows the movement in image calculation without error. The vertical axis represents the movement of the image plane in the optical axis direction (full scale corresponds to 2 mm of the image plane), and the horizontal axis represents time (full scale is 2.5 seconds). Accumulation and calculation are repeated on the time axis, and (accumulation time + calculation time) is a distance measurement cycle.

A shows the movement of the image by calculation, and B shows the movement of the film surface. D is a range in which the photographer cannot determine the focus shift with the viewfinder, and if the focus is followed within this range, it can be seen that the focus is completely followed. The range of D is ± 42 μm in this example. It can be seen that the body is driven from the initial defocus amount, and the drive locus B on the film surface is completely on the movement locus A on the image surface. However, in reality, since the error is always included, it is not ideally followed in this way.

FIGS. 6 and 7 use a lens having a focal length of 300 mm, and the image plane with respect to time when the subject approaches at 100 km / h (subject distance of 100 m at the start) and away (subject distance of 50 m at the start). In the figure showing the locus of C = 1.
This is an example of following the body (film surface) when 0 (the same as the calculated body driving speed). 8 and 9 have the same conditions as those in FIGS. 6 and 7, respectively, and the difference is that C = 0.5. FIG. 6, where C = 1.0
As compared with FIG. 7, it can be seen that the followability of the film surface is better when C = 0.5.

FIGS. 10 and 11 show the case where the upper limit of 2.0 is set for the image velocity change rate in addition to the conditions of FIGS. 8 and 9. It can be seen that the followability of the film surface is further improved as compared with FIGS. 8 and 9. Although the above-mentioned embodiment is a description of the back-focus AF camera,
It is obvious that the same can be applied to the lens drive type AF camera.

[0022]

As described above, according to the present invention, the predicted image velocity of the image plane of the object and the focus shift amount thereof are obtained, and the driving speed of the focus adjusting member is determined from these data to determine the focus adjusting member. In a predictive focusing device that performs focusing by controlling the speed, by controlling the speed of the focus adjusting member to a driving speed obtained by multiplying the driving speed of the focus adjusting member by a coefficient of 1.0 or less It suppresses the abnormal speed that occurs and enables smooth tracking to the in-focus position.
Further, by setting an upper limit on the ratio of image velocities, it is possible to suppress an abnormal velocity similarly caused by a distance measurement error, and by using it in combination with the drive speed condition of the focus adjusting member, a smoother focusing can be achieved. Enables tracking of position.

[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 a method of setting an upper limit value of an image velocity change rate, and is a graph showing a relationship of an image velocity (mm / S) with respect to a subject distance (m) using a subject velocity as a parameter.

[Fig. 4] 100k using a lens with a focal length of 300mm
FIG. 6 is a diagram showing a locus of an image plane with respect to time when a subject approaches at m / h, and is an example in which movement of a body (film surface) ideally follows a movement in image calculation without error.

FIG. 5: 100 k using a lens with a focal length of 300 mm
It is a figure which shows the locus | trajectory of an image surface with respect to time when a to-be-photographed object goes away at m / h, and is an example in case the movement of a body (film surface) ideally follows the movement in calculation of an image without an error.

FIG. 6 uses a lens having a focal length of 300 mm and is 100 k
FIG. 11 is a diagram showing a locus of an image plane with respect to time when a subject approaches at m / h, and is an example of following a body (film surface) when C = 1.0 with respect to movement in image calculation.

FIG. 7: 100k using a lens with a focal length of 300mm
It is a figure which shows the locus | trajectory of an image surface with respect to time when a to-be-photographed object goes away at m / h, and is an example of following a body (film surface) in case C = 1.0 with respect to the movement in calculation of an image.

FIG. 8: 100 k using a lens with a focal length of 300 mm
FIG. 6 is a diagram showing a locus of an image plane with respect to time when a subject approaches at m / h, and is an example of following a body (film surface) when C = 0.5 with respect to movement in image calculation.

FIG. 9: 100k using a lens with a focal length of 300mm
It is a figure which shows the locus | trajectory of the image surface with respect to time at the time of a to-be-photographed object's moving away at m / h, and is an example of following the body (film surface) in case C = 0.5 with respect to the movement in calculation of an image.

FIG. 10 is a graph showing the result of using a lens having a focal length of 300 mm,
FIG. 3 is a diagram showing a locus of an image plane with respect to time when a subject approaches at km / h, and an example of following a body (film surface) when C = 0.5 and an upper limit value of 2.0 with respect to movement in image calculation. Is.

FIG. 11 is a graph showing the result of using a lens having a focal length of 300 mm,
FIG. 6 is a diagram showing a locus of an image plane with respect to time when a subject is moving away at km / h, where C = 0.5 for movement in image calculation,
It is an example of following the body (film surface) when the upper limit value is 2.0.

[Explanation of symbols]

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

Claims (3)

(57) [Claims] 1. A predicted image velocity and a focus shift amount thereof are calculated by calculating a ratio of a previous image velocity and a current image velocity from a moving velocity of an image plane of a subject which is continuously obtained, and a focus adjusting member is driven from these data. In a predictive focusing device that determines a speed and performs focusing by controlling the speed of the focus adjusting member, an upper limit is set for the ratio of the image velocities, and the determined drive speed is multiplied by a coefficient of 1.0 or less. In controlling the speed of the focus adjusting member to the obtained driving speed
A feature characterized by enabling more tracking to the in-focus position.
Focusing device. 2. The predictive focusing apparatus according to claim 1, wherein the coefficient is set to about 0.5. 3. The ratio of the image velocities is the focal length of the lens,
The predictive focusing device according to claim 1, wherein the upper limit value is determined based on the predicted image speed detection cycle and the image speed.