JPH0714969Y2 - Camera autofocus device - Google Patents

Description

[Technical field] The present invention relates to an automatic focusing device for a camera, and particularly, to prevent a shutter chance from being missed even when an object is temporarily out of a distance measuring zone. Automatic focus device.

[Prior Art and its Problems] Recent single-lens reflex cameras are mainly equipped with an autofocus device. The autofocus device of such a single-lens reflex camera (hereinafter referred to as "AF single-lens reflex camera") measures a part of the aerial image of the object (usually the object around the optical axis) formed by the shooting lens by dividing it into two parts. An image is formed on the light receiving surface of the distance sensor (CCD), a predetermined distance calculation is performed based on the two-divided object image signal from the distance measurement sensor, the defocus amount is calculated, and the focus is determined according to the defocus amount. The lens was driven to the in-focus position and focused. Then, in order to inform the user of the range of the subject to be focused (provided for the distance measurement calculation), a distance measurement zone (frame) is provided within the viewfinder field.

In addition, in the conventional AF single-lens reflex camera, when the shutter button is pressed halfway down, the autofocus device is activated, the distance measurement calculation is executed at predetermined time intervals to obtain the defocus amount, and the focus lens is based on that value. When the lens was driven to the in-focus position and the shutter button was pressed all the way down, the exposure device consisting of the shutter, diaphragm and the like was activated to expose the film.

For the focusing operation, the autofocus device maintains the operating state while the shutter button is pressed halfway, that is, the focusing lens is once moved to the position where the subject in the focusing zone is focused. Even if the subject distance in the distance measuring zone changes, the focus lens is moved to follow this and maintain the in-focus state (hereinafter referred to as "servo AF mode").
There is.

When shooting with such a conventional AF SLR camera,
The user has to put the subject in the range-finding zone described above in order to focus on the subject to be shot.
Alternatively, the camera is moved so as to include the distance measurement zone and the shutter button is pressed.

If the subject is a moving car, for example,
The user, in the servo AF mode, moves the camera while pressing the shutter button halfway while catching the vehicle in the distance measurement zone, and after focusing, fully presses the shutter button at a desired time.

However, in such a conventional camera, when the distance measuring zone deviates from the subject to capture a landscape at infinity or conversely, or when a person enters between the subject and the camera, At present, the focusing operation is performed on the object captured by the distance measuring zone. Therefore, even if the subject is captured in the distance measurement zone again, it may take time before the subject is focused again, and in some cases, the shutter chance may be missed, and the intended photograph may not be taken.

In particular, the above problem is likely to occur when a moving object such as an automobile moving at high speed is photographed using a super telephoto lens having a long focusing time.

[Object of the Invention] The present invention has been made in order to solve such a conventional problem.
To provide an autofocus device that stops the focusing operation when the subject distance changes abruptly after focusing once, and performs the focusing operation again when the subject distance at the time of focusing is approached. To aim.

[Outline of the Invention] In order to achieve the above object, the present invention combines a distance measuring unit that repeatedly measures an object distance at a predetermined time interval and a focusing lens based on the object distance information measured by the distance measuring unit. A lens driving unit that drives to a focus position, a focus determination unit that determines whether or not focus is achieved, a storage unit that stores subject distance information when the focus determination unit determines that focus is achieved, and a subject An allowable change amount storage unit that stores an allowable change amount related to distance information, and when the focus determination unit determines that the object is in focus, the subject distance information at that time is stored in the storage unit, and then measured by the distance measurement unit. The absolute value of the difference between the current subject distance information and the stored subject distance information is compared to see if it is larger than the allowable change amount. It is characterized in that focus control means for activating the lens drive means and not operating the lens drive means if large is provided.

According to the above configuration, even when the distance measuring zone is temporarily separated from the subject and the subject is captured again in the distance measuring zone during moving object shooting, the subject is not focused until the subject is focused again. It will not take much time. Therefore, in the above case, the possibility of missing a photo opportunity is reduced, and the user can take an intended photograph.

Embodiments of the Invention Next, embodiments of the focusing device of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram of the autofocus device of the present invention.
As shown in the figure, the distance measuring unit 11 as a distance measuring unit that measures the distance to the subject and outputs a signal related to the distance.
Is connected to a focus control section 12 as a focus determination means and a focus control means for generally controlling the operation of the autofocus device of the present invention. The distance measuring unit 11 is a known distance measuring sensor (CC
D), and a part of the aerial image of the subject (usually the subject around the optical axis) formed by the taking lens is guided to the light receiving surface of the distance measuring sensor in two. Then, the distance measuring sensor outputs an image signal regarding each of the two divided images to the focus control unit 12.

In addition, the focus control unit 12 includes the focus lens of the shooting lens.
A lens drive unit 13 that drives 18 is connected via a lens drive circuit 14 that drives the lens drive unit 13.
The lens drive unit 13 has an AF motor as a power source,
The lens driving circuit 13 and the lens driving circuit 14 constitute lens advance driving means.

Up to this point, a feedback system for focusing is configured, and the focusing control unit 12 normally obtains the defocus amount based on the pair of image signals output from the distance measuring unit 11, and the lens based on this value. Drive unit 13 and lens drive circuit 14
Focus lens to focus on the target subject by
18 will be driven.

In addition, the focus control unit 12
It is output from the release button 15 that causes the shutter 12 to perform the above-described focusing operation and releases the shutter when it is fully pressed, and the distance measuring unit 11 when the focus control unit 12 determines that the subject is in focus. Subject distance storage unit 16 as a storage unit that stores information about the subject distance, and the distance to the current subject measured by distance measuring unit 11 and subject distance storage unit 16
The permissible change amount storage unit 17 as the permissible change amount storage unit that stores the permissible change amount with respect to the distance to the subject at the time of focusing stored in is connected.

The focus control unit 12 functions by pressing the release button 5 halfway, and when it is determined that the focus is achieved during the above-described focus operation, the focus distance control unit 12 stores in the subject distance storage unit 16 the distance measuring unit at the time of the focus. The information regarding the distance output from 11 is stored.

Then, after that, the amount of change between the distance stored in the subject distance storage unit 16 and the distance currently output from the distance measuring unit 11 is smaller than the allowable change amount stored in the allowable change amount storage unit 17. Judge whether it is large or not.

As a result of this determination, if the amount of change is larger than the allowable amount of change, the focusing operation is stopped so as to maintain the current state, and if it is smaller, the normal focusing operation described above is performed.

The autofocus device of the present invention thus constructed operates in the following general manner in actual use. This operation will be described with reference to FIGS. 2 (A) and 2 (B).

As shown in the figure, consider a case where a user photographs an airplane in flight as a subject. When shooting an airplane moving at such a high speed, as shown in FIG.
While looking through the viewfinder, the user moves the camera so that the airplane 20 is located within the distance measuring zone 19. When the release button 15 is pressed halfway in this state, the focusing lens 18 is driven so as to always focus on this airplane.

However, when the user cannot follow the airplane 20 and the airplane 20 deviates from the distance measuring zone 19 as shown in FIG. 2 (B), the lens position that was focused immediately before is maintained.

Then, when the user moves the camera and again captures the airplane 20 in the distance measuring zone 19 as shown in FIG. 2 (A), as described above, the lens is always focused on this airplane. Is driven.

Therefore, even if the subject is lost, the focus can be achieved in a short time when the subject is captured again.

The above operation may be performed uniformly in the control of the camera, or a mode for intentionally performing such an operation may be provided and performed when this mode is selected. Good.

Further, the above focusing operation will be described in detail with reference to the flowcharts shown in FIGS. This operation is performed by the CPU according to the program stored in the ROM in the focus control section 12. In normal camera operation, AE calculation processing for obtaining exposure values such as shutter speed and aperture value, exposure processing for exposing the film by operating the shutter and aperture based on the exposure value, film winding processing, and other Although the processing is executed, it will not be described because it is unnecessary for understanding the present invention.

FIG. 3 is a flow chart of mode setting when the camera performs the focusing operation as shown in this embodiment. When setting the mode, first, the mode switch provided on the body of the camera is operated to select the servo AF mode (step 21). When this mode is selected, the camera is set to servo AF mode (step 22). As described above, this mode may be performed uniformly as a series of control of the camera.

Next, FIG. 4 is a flowchart for monitoring the state of the switch (release button 15) for executing the above-described focusing operation. This process is periodically performed at predetermined time intervals by a timer interrupt.

First, when an interrupt signal is output, the release button 15 is pressed, that is, whether the release button 15 is not pressed at all, is in a half-pressed state, or is in a fully-pressed state ( Step 31).

Then, if the release button 15 is half-pressed, the process proceeds to a subroutine relating to focusing processing (step 32), and if it is not half-pressed but full-pressed, exposure processing is executed and then END processing is performed (steps 33 and 34). If it is neither half-pressed nor full-pressed, it proceeds to END processing and waits for the timer interrupt to be applied again. In the exposure processing, photometry and AE calculation are executed before the exposure operation to the film, and the film is wound up by one frame after the exposure.

In short, this interrupt subroutine
This is for periodically monitoring whether is pressed halfway.

The sub-routine relating to the focusing processing to be carried out here is a sub-routine relating to the AF mode set in the mode setting sub-routine. Since the servo AF mode is selected in this embodiment, the processing advances to the servo AF sub-routine.

FIG. 5 is a main flowchart for the servo AF operation of this embodiment. This process is shown in FIGS. 1 and 2 (A).
A description will be given with reference to (B) and.

In step 41, it is checked whether or not the release button 15 is half pressed, and if it is half pressed, step 42
If not, proceed to END processing.

In step 42, it is checked whether or not the release button 15 is fully pressed. If not fully pressed, the process proceeds to step 4, and if fully pressed, the exposure process is performed. In the exposure processing, photometry and AE calculation are executed before the exposure operation to the film.

In step 43, the distance measuring unit 11 is activated to measure the distance, and the focus control unit 12 executes the distance measuring operation based on the distance measuring signal to calculate the defocus amount (the rotation speed and the rotation direction of the AF motor). )
Ask for. Then go to step 44.

In step 44, the lens driving unit 13 is driven via the lens driving circuit 14 to move the focusing lens 18 in the focusing position direction. Then, it proceeds to step 45.

In step 45, it is checked whether or not the focusing lens 18 has moved to the in-focus position, that is, whether or not it is in focus. If it is not in focus, the process returns to step 41 to continue the focus operation, and if it is in focus, the process proceeds to step 46.

In step 46, the subject distance L at the time of focusing is stored and the process proceeds to step 47.

In steps 47 and 48, the state of the release button is judged in the same way as in steps 41 and 42, and if the release button 15 is not fully pressed but half pressed
Proceed to 49.

In step 49, distance measurement processing is executed to obtain the subject distance (distance measurement distance L ₀ ). Then go to step 50.

In step 50, it is checked whether or not the absolute value of the difference between the in-focus distance L and the distance-measuring distance L ₀ is larger than the allowable change amount A stored in the focus control section 12. In other words, check if the subject distance has changed drastically. If it has changed abruptly, the process of moving the focusing lens is not executed and the process returns to step 47. If it has not changed, the process proceeds to step 51.

Through the above processing, it is determined whether or not the distance to the subject has suddenly changed significantly. In other words, as shown in FIG. 2 (B), it is judged whether or not the subject is out of the distance measuring zone.

In step 51, the focus lens is calculated based on the distance measurement distance L _0.
A lens driving process for driving 18 is executed, and the process proceeds to step 52.

In step 52, it is checked whether or not the subject is in focus. If it is not in focus, step to execute focus processing again
Returning to 47, if in focus, proceed to step 53. If the distance measurement distance L ₀ measured in step 49 returns to step 47 and is larger than the allowable change amount A, the operation of the lens drive unit 14 is stopped or the object distance storage unit 16 stores It is operated so as to focus on the determined subject distance L.

In step 53, the distance-measuring distance L ₀ is stored as the subject distance L when focusing, the process returns to step 47, and the above-mentioned processing is repeated.

In short, the present auto-focusing device determines whether or not the subject distance (distance-measuring distance L ₀ ) suddenly changes greatly once the subject is in focus, in other words, as shown in FIG.
It is determined whether 20 is out of the distance measuring zone 19 (step 50). As a result of this determination, if the amount of change is equal to or less than the allowable amount of change A, the focusing lens 18 is driven so that the in-focus state is always maintained (step 51), and the subject distance L is updated each time the in-focus state is achieved. Yes (step 53). Then, the above-mentioned processing is repeated while the half-pressed state of the release button 15 is maintained (step 47 to step 53).

On the other hand, when the subject moves out of the distance measuring zone 19, the change in the subject distance L and the distance measuring distance L ₀ at the time of focusing is larger than the allowable change amount A, provided that the release button 15 is half pressed. Only the determination as to whether or not it is repeated is stopped, and the driving of the focusing lens 18 is stopped until it becomes small (steps 47 to 50).

In addition, while the focusing and lens driving unit 13 repeats the focusing operation after focusing once, the focusing distance L ₀ (step 47
If the measured distance L ₀ measured in step 49 is greater than the allowable change amount A, the lens drive unit 13 is stopped, but the object distance L stored in the object distance storage unit 16 is stopped. Alternatively, the focusing operation may be performed with respect to the distance-measuring distance immediately before the allowable variation amount A is exceeded.

The in-focus object distance L stored in the object distance storage section 16 is initialized when the release button 15 is turned off.

As described above, in the autofocus device of the present invention, when the subject distance changes rapidly after focusing, the lens driving operation is not performed, so that the time required for refocusing can be shortened. If the amount of change in the subject distance is within the allowable amount of change, the operating distance during focusing is always set, so that it is possible to follow the moving subject.

Although the change amount is used as the parameter for determining whether or not the lens driving operation is performed, the change rate may be used. Also, the subject distance was used as the same criterion,
The defocus value or the image magnification obtained by the CCD image sensor may be used instead of the object distance.

Further, it is preferable that the allowable change amount is changed according to the focal length of the lens and the subject distance at the time of focusing. For example, the longer the focal length of the lens, the smaller the distance, and the shorter the in-focus object distance, the smaller.

[Effects of the Invention] As is clear from the above description, in the automatic focusing device of the present invention, the distance information suddenly changes once the focus is achieved during continuous distance measurement and focus operation. In this case, the focusing operation is stopped and the focusing operation is performed again when the distance information approaches the information before the rapid change. Even when the target object is temporarily removed and the desired object is captured again in the distance measurement zone, the focusing time when the desired object is captured again is shortened, so the user misses a photo opportunity. You're less likely to be able to take the picture you want.

[Brief description of drawings]

FIG. 1 is a block diagram of an automatic focusing device according to the present invention, FIGS. 2 (A) and 2 (B) are operation explanatory views of the automatic focusing device according to the present invention, FIGS. 3, 4, and 5. The figure is an operation flowchart of the autofocus device according to the present invention. 11: Distance measuring unit (distance measuring unit), 12: Focus control unit (focus control unit), 13: Lens drive unit (lens drive unit), 14
...... Lens drive circuit (lens drive means), 15 ...... Release button, 16 …… Subject distance storage section (storage means), 17 ・ ・ ・
... Allowable change amount storage unit (allowable change amount storage means)

Claims (1)

[Scope of utility model registration request] 1. Distance measuring means for repeatedly measuring a subject distance at predetermined time intervals, lens driving means for driving a focusing lens to a focusing position based on subject distance information measured by the distance measuring means, and focusing. Focus determination means for determining whether or not, storage means for storing subject distance information when the focus determination means determines focus, and allowable change amount for storing allowable change amount regarding subject distance information When the storage means and the in-focus determination means determine in-focus, the subject distance information at that time is stored in the storage means, and then the current subject distance information measured by the distance measuring means and the stored subject distance. Whether the absolute value of the difference from the information is larger than the allowable change amount is compared, and if smaller, the lens driving means is operated based on the current object distance information, Re If the camera autofocus apparatus being characterized in that and a focusing control unit not to operate the lens driving means.