JPH01185083A - focus adjustment device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a focus adjustment device suitable for use in video cameras and the like.

[Conventional technology]

Conventionally, in video cameras and still cameras,
Automatic focus adjustment devices are widely used and have been extremely effective in improving operability.

There are various methods for automatic focusing devices, including a type that has a light emitting means and a light receiving means on the device side and measures the distance to the subject by detecting the reflected light of the light emitted by the light emitting means with the light receiving means. There are methods that have a dedicated optical system for focus detection, such as methods that measure distance from the deviation of object images incident on objects or paths with different optical path lengths; It can be roughly divided into two types: those that adjust the focus by detecting the in-focus point from the video signal output from an image sensor, etc. that converts it into a signal, but in recent years, the latter method has begun to require no dedicated optical system. In addition, because the focus is detected from the video signal itself, it is possible to perform more accurate focus detection on the subject.
Widely used.

[Problem to be solved by the invention]

However, in the above-mentioned automatic focus detection device, since the in-focus state is detected from the video signal output from the image sensor, especially the high-frequency component in the video signal, it is affected by the shape of the subject, the pattern, etc. For example, in the case of a subject whose entire surface is not fine, it may not be possible to obtain a sufficient detection output to indicate that the object is in focus, even if the object is in focus, and the imaging lens or image sensor may be moved to a close position without being able to detect the in-focus position. There was a problem in that it was impossible to take pictures because the reciprocating movement was repeated between the position and the infinite position.
This problem can also occur in low overall illumination.

In order to solve this problem, conventional methods have been used such as stopping the imaging lens or image sensor at the close end, infinity end, or the position before movement when the in-focus position cannot be detected. The position of the camera does not necessarily match the distance from the subject you are trying to photograph, so
Even with this method, it was not possible to accurately obtain the in-focus position.

(Means for Solving the Problems) The first object of the present invention is to solve the above-mentioned problems. a focus detection means for detecting a focus state of the object from a video signal output from the image pickup means; and a relative distance between the imaging lens and the imaging surface based on the detection result of the focus detection means. By providing a focus adjustment means that is displaced and a switching means that enables manual operation of the focus adjustment means when the focus position cannot be detected by the focus detection means, when automatic focus detection is impossible, This allows automatic switching to manual focus adjustment operation to prevent photographing in an out-of-focus state.

A second object of the present invention is to prevent malfunctions caused by erroneously operating the manual focus adjustment means during the automatic focus adjustment operation. , with means for inhibiting manual focusing operations.

A third object of the present invention is to display a message to make the operator aware that the automatic focus adjustment operation mode has been switched to the manual focus adjustment operation mode.

A fourth object of the present invention is to maintain a constant operational feel regardless of the focal length of the optical system, especially in manual focus adjustment operations.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the automatic focus adjustment device according to the present invention shown in the drawings will be described in detail below.

FIG. 1 is a block diagram showing a first embodiment of the present invention. In the same figure, 1 is an imaging lens, and 2 is a system for converting a subject image formed on an imaging surface by an optical lens 1 into an electrical signal, e.g. An imaging device such as a CCD, 3 is a supporting member arranged to support the imaging device 2 and move back and forth on the optical axis of the imaging lens 1 (a well-known means is used for the supporting means, and the illustration is not shown). (omitted), 4 is a motor as a driving means for moving the support member 3 in the optical axis direction, a lead screw 48 directly connected to the rotating shaft of the motor is screwed into the support member, and the support member is moved by rotation of the motor. I now work 6 shifts before and after my 3rd shift. Reference numeral 5 denotes a motor control circuit for driving and controlling the motor 4, which operates to drive the motor 4 based on the output of a focus detection circuit 8, which will be described later, and to position the image pickup device 2 to a focus matching position. Also 12
directly operates the motor control circuit 5 to drive the motor 4,
This is a manual focus adjustment operation button for moving the image sensor 2 to a desired position, and the focus can be adjusted by moving the image sensor back and forth while viewing a monitor image. By pressing the operation button in the manual focus adjustment mode, a drive signal corresponding to the direction is generated while the button is pressed, and the motor control circuit 5 drives the motor 4 according to this drive signal to take an image. The element 2 is moved in a predetermined direction. This allows manual focus adjustment.

6 is a video signal processing circuit that performs various signal processing such as blanking processing, addition of a synchronization signal, and gamma correction to the video signal output from the image sensor 2 and converts it into a television signal; 7 is a video signal processing circuit This is an electronic viewfinder connected to the output terminal 6a of the camera 6 and used to monitor the image that is incident on the image sensor 2.

Reference numeral 8 denotes a focus detection circuit for detecting a focused point, that is, a focus position where the imaging state on the imaging surface of the image sensor 2 is the best, based on the video signal supplied from the image sensor 2 to the video signal processing circuit 6. For example, as shown in this embodiment, there is a bypass filter (HPF) 81 that extracts a signal obtained by amplifying the output signal of the image sensor 2 to a predetermined level and extracts a predetermined high frequency component in the signal. Detection circuit 82) The detection circuit 82 detects the high frequency components extracted by the detection circuit 82 and outputs a focal voltage according to the degree of detail of the subject.) The focal voltage output from the detection circuit 82 is sampled and held at regular intervals, and the amount of time change in the focal voltage is calculated. The output of the differential hold circuit 83 is supplied as a motor drive signal to the motor control circuit 5 via a focus adjustment mode switching circuit, which will be described later. The signal output from the differential hold circuit 83 exhibits a characteristic that the polarity is reversed to positive and negative before and after O2 at the in-focus position, and the motor control circuit 5 drives the motor 4 based on this signal to bring the image sensor 2 into focus. Automatically moves to the focus position.

Reference numeral 9 is arranged between the focus detection circuit 8 and the motor drive circuit 5, and determines whether or not automatic focus adjustment is possible based on the signal obtained from the focus detection circuit 8 according to the degree of focus, and determines the determination result. The 6-focus adjustment mode switching circuit 9 is a focus adjustment mode switching circuit that switches between automatic and manual focus adjustment according to 5 and drives the motor 4 based on the output of the focus detection circuit 8 to enable automatic focus adjustment, and disables the operation of the manual operation button 12 by the control signal 9a. In addition, when the subject is a subject for which no change in high-frequency components can be obtained even if the image sensor is moved, and a focus detection signal cannot be obtained over the entire moving range of the image sensor 2, the focus detection signal is not supplied to the motor control circuit 5. At the same time, the control signal 9a is turned off to enable the manual operation button 12, and a manual focus adjustment mode is established.

Reference numeral 10 denotes a display circuit for displaying the state when the focus adjustment mode switching circuit 9 is switched to the manual mode. It is designed to be displayed.

In addition, when the subject changes and a focus detection signal can be obtained, the focus operation mode switching circuit 9 switches the focus detection circuit 8 again.
An automatic focus adjustment mode is entered in which the position of the image sensor 2 is controlled based on the output signal of.

In the figure, 11a and flb detect both ends of the movable range of the image sensor 2, that is, the closest end and the infinite end, and convert the detection results into predetermined signals via the switch circuit 11. This is a micro switch for output.

The present embodiment has the above configuration, and its operation will be explained next.

A subject image formed on the imaging surface of the image sensor 2 through the image sensor 1 is converted into an electrical signal by the image sensor 2, and then supplied to the video signal processing circuit 6, where it is converted into a television signal. The image is output to the output terminal 6a and monitored by the electronic viewfinder 7.

On the other hand, the video signal supplied to the video signal processing circuit 6 is supplied to the focus detection circuit 8, where a focus detection signal is output as the image sensor 2 is moved by the motor 4.

Note that the focus operation switching circuit is normally in automatic focus adjustment mode, and in this state, the motor 4 is driven based on the focus detection signal output from the focus detection circuit 8, and the image sensor 2 is moved to the in-focus position. will be moved. In addition, the manual operation button 12 is disabled by the control signal, and a safety measure is taken to prevent the relative position between the imaging lens 1 and the image sensor 2 from shifting even if the manual operation button is accidentally operated during automatic focus adjustment. There is.

Here, in a state where it is difficult for the focus detection circuit to detect the focus, such as when the subject itself does not have fine details and high frequency components are difficult to detect, the output level of the focus detection signal is lower than that of the focus detection circuit 8. Even if the image sensor 2 is moved on the optical axis, there is no change in the focus detection signal, and the in-focus position cannot be detected. In this embodiment, the microswitch 11a.

fib detects the six ranges of the image sensor 2, and if focus cannot be detected even after six ranges from the closest end to the infinity end, it is determined that automatic focus adjustment is impossible, and the focus is The adjustment mode switching circuit 9 switches from automatic focus adjustment mode to manual focus adjustment mode, and the focus detection circuit 8
At the same time, the control signal 9a is turned off, that is, the supply to the motor control circuit 5 is stopped, and the manual operation button 12 is made operable.

As a result, the motor control circuit 5 is operated by the manual operation button 12 regardless of the output of the focus detection circuit 8, and the image pickup device 2 can be manually moved to the in-focus position.

At the same time, the fact that the mode has been switched to the manual focus adjustment mode is displayed on the screen of the electronic viewfinder 7 via the display circuit 10 together with the video signal.

Figure 2 shows an example of such a display in the electronic viewfinder. Normally, in automatic focus adjustment mode, "AUTO" is displayed, and in manual focus adjustment mode, "MANUAL" is displayed. However, it goes without saying that other display methods may be used.This allows the photographer to easily recognize the current focus adjustment mode and perform appropriate operations.

Note that the focus operation switching circuit 9 detects the level of the focus detection signal output from the focus detection circuit 8 even during the manual focus adjustment mode, and when the level reaches a predetermined level or higher and focus detection becomes possible, as described above again. It operates to switch to automatic focus adjustment mode.

FIG. 3 is a flowchart showing a portion of the above-mentioned focus adjustment operation.

At the start of the focus adjustment operation, the automatic focus adjustment mode is selected by the focus adjustment mode switching circuit 9 (step
l), the manual operation button 12 is disabled by the control signal 9a to prevent erroneous operation (step 2). Subsequently, the image sensor 2 is moved in accordance with the focus signal output from the focus detection circuit 8, and the process proceeds to 5tep3. If the focus is found, the process proceeds to 5tep4 to stop the automatic focus adjustment operation. If there is a change in the focus signal at step 5, it is determined that the focus is out of focus, and the process returns to step 5 and the automatic focus adjustment operation is performed again.

On the other hand, if the focal point is not in focus at 5tep3,
Proceeding to step 6, the microswitches lla and 11b detect whether or not the image sensor 2 is at the end of the direction in which it is currently moving, and if it has not reached the end, the 5tepl
Return to the previous page to continue automatic focus adjustment. If the end is reached, the process proceeds to 5tep7, where the motor 4 is reversed to reverse the moving direction of the image sensor 2, and the focus adjustment operation is continued at 5tep8. If the focal point is determined at 5tep9, the process proceeds to 5tep4, and the focus adjustment operation is stopped as described above. Also, if it is not in focus at 5tep9, the process proceeds to 5teplo, and it is determined whether or not it is at the end in the current (after reversal) movement direction, and if it is not at the end, it is moved to 5tep8.
Return to and continue adjusting the focus, and if it is at the edge, adjust the focus to 5 tepH.
The automatic adjustment operation is stopped in step 5, and in step 12, the focus adjustment mode switching circuit 9 cancels the control signal 9a and switches to the manual focus adjustment mode. This allows focus adjustment to be performed using the manual operation button 12. The process then proceeds to step 513, where a message indicating that the manual mode has been switched is displayed on the screen of the electronic viewfinder 7.

Note that even in the manual focus adjustment mode, the focus signal is output from the focus detection circuit 8, and if the signal level reaches a level sufficient to enable focus detection in the focus signal at 5tep9, or if a change occurs, the focus signal returns to 5tepl and is output again. It becomes normal automatic focus adjustment mode.

FIG. 4 is a block diagram showing a second embodiment of the present invention.

Here, if the optical system including the imaging lens is a zoom lens 1' that can vary the focal length, the distance required to move the imaging device from the close end to the infinity end, that is, actually focus on the subject. There is a property that the amount of movement of the image sensor to achieve this change varies greatly depending on the focal length of the lens optical system. Therefore, if you ignore the focal length of the imaging lens and adjust the focus by moving the imaging element at a constant speed, the focusing speed will vary greatly depending on the focal length of the lens, resulting in poor operability.
There is a risk that it will be difficult to perform accurate focusing operations.

Here, the focal pressure l11f (mm) of the lens optical system, and the distance l from the imaging surface of the image sensor at each focal length from the infinity end.
! Amount of movement 1al required to focus on position l1tR
When tx (mm), these relationships are as shown in the following equation.

Figure 5 is a characteristic curve showing this relationship, where the horizontal axis shows the focal length f of the lens optical system and the vertical axis shows the amount of movement of the image sensor @X when distance R is used as a parameter, making it easy to understand. In order to Become.

Now, assuming a 6x zoom lens with f: 8mm to 48mm, f = 8mm and x = 0.065mm.

When f=48 mm, x=2.55 mm, and there is a difference of about 39 times in the amount of movement between the Te1e end and the Wide end of the zoom lens.

Therefore, when performing manual focus adjustment, it is difficult to manually compensate for the difference in the amount of movement described above, and good focus adjustment cannot be performed.

This embodiment solves this problem by detecting the focal length of the zoom lens using an encoder and controlling the moving speed of the image sensor according to the focal length. The focusing speed remains unchanged, greatly improving operability.

In FIG. 4, the same reference numerals are used for the same components as in the first embodiment in FIG. 1, and the explanation thereof will be omitted.

The difference from FIG. 1 is that a focal length detector, for example, a zoom encoder 13, is used to detect the focal length of the imaging lens 1'.
The output of the zoom encoder 12 is supplied to the motor control circuit 5', and the motor 4 is driven by calculating the output of this output and the output of the focus detection circuit. Therefore, the motor control circuit 5' controls the speed of the motor 4 to become slower as the focal length of the lens optical system becomes smaller, based on the characteristic curve shown in FIG. This means that a constant focusing speed can be maintained regardless of the focus.

Next, the operation of the above embodiment will be explained.

As in the first embodiment, the automatic focus adjustment mode is normally set, and the motor control circuit 5 is operated based on the focus detection signal output from the focus detection circuit 8 to automatically move the image sensor 2 to the focus position. It is in a state where it is controlled as if it is working hard.

If a sufficient focus detection signal is not obtained here and the focus adjustment operation switching circuit 9 switches to manual adjustment mode, the command is supplied to the motor control circuit 5' by operating the manual operation button 12 in the same way as described above. Based on this, the motor 4 is driven and the image sensor 2 is moved. Here, the Chiyo control circuit refers to the focal length of the imaging lens detected by the encoder 11 and calculates the focal length based on the above-mentioned equation (1). A calculation is performed to determine the amount of movement X of the image sensor 2. Therefore, the travel time of the image sensor 2 from close object distance to infinity is controlled so that it is always constant anywhere from the Te1e end to the Wide end, regardless of the focal length of the lens. Can be done.

In this way, the movement speed of the image sensor is changed according to the focal length of the imaging lens, and the focal point can be displaced at a constant speed, so the feeling of manual focus adjustment is always constant, making focus adjustment accurate and easy. becomes.

In each of the above-mentioned embodiments, the imaging lens is fixed and the focus adjustment is performed by moving the imaging element side. It is possible.

〔Effect of the invention〕

As described above, according to the automatic focus detection device of the present invention,
The state of the subject during automatic focus adjustment.

When the in-focus position becomes impossible to detect due to the environment, we immediately switch to manual focus adjustment mode, so the imaging lens or image sensor continues to move back and forth without being able to detect focus, or if it moves to a position that is not in focus. This can eliminate inconveniences such as stopping.

Furthermore, since the manual focus adjustment operation is disabled in the automatic focus adjustment mode, even if the manual operation member is operated by mistake during the automatic focus adjustment operation, there will be no malfunction due to this, and the operation is reliable.

In addition, the display indicates that the automatic focus adjustment mode has been switched to the manual focus adjustment mode, so the operator can always accurately grasp the operating status of the device and can prevent erroneous operation. can.

In addition, when performing manual focus adjustment, the moving distance of the optical system, which changes depending on the focal length of the optical system, is compensated for by varying the speed of the focus drive system, making it possible to eliminate variations in focusing speed. can improve sexual performance.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a first embodiment of a focus adjustment device according to the present invention, FIG. 2 is a diagram showing an example of a mode display on the monitor screen of an electronic viewfinder, and FIG. 3 is a block diagram showing a first embodiment of a focus adjustment device according to the present invention. FIG. 4 is a flowchart for explaining the operation, FIG. 4 is a block diagram showing a second embodiment of the present invention, and FIG. 5 is a characteristic diagram showing the relationship between the focal length and the moving distance of the optical system.

Claims (6)

[Claims] (1) an imaging means for converting the subject image formed on the imaging surface by the imaging lens into an electrical signal; a focus detection means for detecting the state of focus on the subject from the video signal output from the imaging means; a focus adjustment means for displacing the relative distance between the imaging lens and the imaging surface based on the detection result of the focus detection means; and the focus adjustment means can be operated manually when the focus position cannot be detected by the focus detection means. 1. A focus adjustment device comprising a switching means. (2) In claim (1), when the focus adjustment means is being driven based on the detection result of the focus detection means, means for prohibiting the manual operation of the focus adjustment means; A focus adjustment device comprising: (3) Claim (1) or (2), characterized in that the feature includes mode display means for displaying when the focus adjustment means is manually switched by the switching means. Focus adjustment device. (4) Claim (3), further comprising a focal length detection means for detecting the focal length of the imaging lens, and controlling the operating speed of the focus adjustment means in accordance with the output of the focal length detection means. A focusing device characterized in that it is configured as follows. (5) an imaging means for converting the subject image formed on the imaging surface by the imaging lens into an electrical signal; a focus detection means for detecting the degree of focus on the subject; and a focus detection means based on the detection result of the focus detection means. a first focus adjustment means for setting the relative position between the imaging lens and the imaging means; and a second focus adjustment means for setting the relative position between the imaging lens and the imaging means independently of the focus detection means. and a control means for disabling the operation of the second focus adjustment means when the first focus adjustment means is operating. (6) Claim (5), characterized in that it includes a switching means for switching between the first focus adjustment means and the second focus adjustment means based on the output of the focus detection means. Focus adjustment device.