JPS6345980A - Automatic focus controller - Google Patents

Abstract

PURPOSE:To select a focusing range as desired by extracting a high frequency component as to a part relating to a specific region in a picture by an area specifying means. CONSTITUTION:A composite synchronizing signal 30 synchronously with a video signal 6 is separated to a vertical synchronizing signal and a horizontal synchronizing signal by a vertical synchronizing signal separator 28 and a horizontal synchronizing signal separator 29 respectively, which trigger window pulse generator 31, 32 and a signal is produced, where the vertical and horizontal directions are gated by a window pulse. By turning on the switch 34, part of the picture is masked and the specific area in the picture is used as a focusing range to apply focus control. In when the circuit constants of the window pulse generators 31, 32 are variably or semi-fixedly designed, the focusing range in the picture is selected further in a board range.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an automatic focus control device applied to television cameras and electronic still cameras.

[Conventional technology]

2. Description of the Related Art A device for automatically focusing a target object in a television camera or the like is already known (for example, Japanese Utility Model Publication No. 40-26568).

This type of device is particularly effective under conditions where it is necessary to follow a moving subject to obtain a focused state. Among these types of devices, the method described in the above publication is generally called a passive method, and is configured to perform focusing adjustment so as to maximize the high frequency component of the output of the imaging means.
Unlike the so-called active method, there is no need to specially install a projection means such as infrared light for focus detection, and therefore it can operate with relatively low power, so it is particularly suitable for small portable television cameras, etc. .

[Problem that the invention seeks to solve]

In the device described in this publication, the direction of defocus is detected by constantly vibrating the movable lens of the camera using a focus fine adjustment device, and based on this, the direction of focus adjustment is adjusted. The direction of movement of the lens is automatically identified.

On the other hand, the range to be focused within the imaging screen usually varies depending on the user's needs. That is, when photographing a person located in the center of the screen against a background of a distant forest or mountain range, the focus area should be a predetermined area in the center of the screen that includes the -1-half of the person's body. ) When photographing sports events such as tennis or American football, the subject moves often, so it is desirable to focus on almost the entire screen.C7.・Tsu.

Furthermore, if you want to focus on a relatively small specific subject within the frame, such as a small bird flying between the trees,
Alternatively, during wide-angle photography, there is a demand to limit the focus range to a relatively small area within the screen.

However, the conventional devices described above do not meet such demands.

The present invention has been made in view of the above-mentioned points, and it is an object of the present invention to provide an automatic focus control device of this type in which a focusing range can be selected as desired.

[Means and effects for solving the problems] In order to solve the above problems, the present invention provides an imaging optical system including elements such as an imaging lens and a photoelectric conversion means for imaging, and an arbitrary operation by an operator. an area specifying means for specifying a portion related to a predetermined area within the screen with respect to the output of the imaging photoelectric conversion means based on the above, and a predetermined element in the imaging optical system that is vibrationally displaced in the optical axis direction, vibrating means for modulating the relative position between the imaging position in the imaging optical system and the image plane of the photoelectric conversion means for imaging; a high frequency component extracting means for extracting a high frequency component of a portion related to the region specified by the means; and a predetermined element in the imaging optical system in a direction that maximizes the output level of the high frequency component extracting means. By means of the first region specifying f, a focus adjustment operation is performed based on the image output regarding the focus target range within the screen.

〔Example〕

First, the mechanical configuration will be explained with reference to FIG.

Reference numeral 1 designates a camera lens assembly, in which an imaging tube 3 as an imaging photoelectric conversion means is disposed on the optical axis of an imaging lens 2 of this assembly 1, and input light 4 given through the lens 2 is transferred to the imaging tube 3. %z so that the image is formed on the target 3a.

The imaging optical system according to the present invention includes the imaging lens 2 and the imaging tube 3. The target computer 3a is connected to a video processor 5, and the output from the target computer 3a is subjected to signal processing and output as a video image 6. In FIG. 1, illustration of a deflection circuit and the like necessary for the image pickup tube 3 is omitted.

On the other hand, a gear 7 is formed on the circumferential surface of the assembly 1, and this gear 7 meshes with a gear 10 provided on the rotating shaft of a DC reversible motor 9 via a gear 8, so that the assembly 1 is rotated by the rotation of the motor 9. By doing this, the focal length is controlled.

Next, the electric circuit will be explained with reference to FIG. Reference numeral 11 denotes an analog gate into which the above-mentioned video signal 6 is input, and on the output side of this analog gate 11 there are a differentiation circuit 12, a detection circuit 13,
A voltage amplifier 14, a bandpass filter 15 and a sampling hold circuit 16 are connected in cascade in the above order. A sampling hold circuit 16 is connected to an R terminal of a flip-flop 18 via a level sensor 17 and to one input terminal of a mixer 19. The output terminal of an oscillator 21 is connected to the other input terminal of the mixer 19 via a DC component removal circuit 20. The output terminal of the oscillator 21 is also connected to the sampling signal input terminal of the sampling hold circuit 16 via the delay circuit 22 and the sampling pulse generator 23 in the above-mentioned order.

Further, the output terminal of the mixer 19 is connected to the above-mentioned DC reversible motor 9 via a current amplifier 24 and is grounded via a transistor 25. This transistor 25 connects its base to the flip-flop 1 through a resistor 26.
It is connected to the b terminal of 8. As shown in the figure, this flip-flop 18 is configured such that its S terminal can be grounded via a switch 27.

On the other hand, 28 is a vertical synchronizing signal separator, and 29 is a horizontal synchronizing signal separator, and a composite synchronizing signal 30 is input to each input side of these synchronizing signal separators 28 and 29. Also, these synchronizing signal separators 28. Each output side of φ9 is connected to an AND gate 33 via a wind pulse generator 3L32.
is connected to the input side of the The output side of this AND gate 33 is connected to the analog gate 11 through a switch (4).

Next, the operation of the apparatus constructed as above will be described. first,
In FIG. 1, when incident light 4 from a subject (not shown) is focused on a target 3a of an image pickup tube 3 through a lens 2, the output of the target 3a is processed by a video processor 5 and output as a video signal 6. Ru. The video signal 6 in this case does not include a composite synchronization signal (vertical synchronization signal and horizontal synchronization signal). As is well known, the frequency components of such video signals vary depending on the degree of focus. In other words, if the incident light 4 is focused on the light-receiving surface, that is, the target 3a, in the best condition, the image will be clear, but if it is poor, the image will be unclear. When the image is blurred, low frequency components increase (that is, high frequency components relatively decrease).

This video signal 6 is applied to a differentiating circuit 12 via an analog gate 11. Here, the analog gate 11 is normally in a conductive state. The differentiating circuit 12 has frequency characteristics as shown in FIG. 3, and is composed of C and R circuits as shown in FIG. 4. As can be easily understood from FIG. 3, the differentiating circuit 12 serves as high frequency component extracting means for extracting high frequency components from the video signal 6. As mentioned above, the better the in-focus state, the more high-frequency components of the video signal will be present, so the output level of the differentiating circuit 12 will change depending on the degree of focus, and the best focus will be achieved. maximum output voltage will occur when the

The output of the differentiating circuit 12 is detected by a detection circuit 13 and voltage amplified by an amplifier 14. Here, since the detection circuit 13 converts the output of the differentiating circuit 12 into a DC signal, it is necessary to have a sufficiently large time constant, but if this time constant is too large, the response time of the control will become long, so the optimal It is necessary to set it to a value. Here, FIG. 5 shows operating waveforms of the differentiating circuit 12 and the detection circuit 13. In the figure (a
l is the waveform of the video signal, (bl is the output waveform of the differentiating circuit 12, and ((+) is the output waveform of the detection circuit 13. Also, the relationship between the output of the detection circuit 13 and the focal length is shown in FIG. 6. As already explained, the output voltage of the detection circuit 13 reaches the maximum level in the state of best focus.In this case, the focal length is adjusted by displacing a predetermined element in the imaging optical system such as a lens. When is modulated by a modulation signal of a constant frequency, that is, when modulation is applied in the sine waveform state shown at a in the focused state at point A in FIG. It produces an output similar to a.The modulation of the focal length is performed by rotating the DC reversible motor 9 left and right by a constant width to apply so-called vibration to the element in the imaging optical system, for example, the lens 2. This vibration is obtained in the following manner. That is, the oscillator 21 generates an output that becomes the original signal of the vibration frequency. This output is sent to one side of the mixer 19 via the DC component removal circuit 20. Here, the DC component removal circuit 20 includes a capacitor, removes the DC component of the oscillator 21, and sends only -10= of the modulated signal component to the mixer 19. The reason for this is that when the DC component is applied from the mixer 19 to the DC reversible motor 9, which will be described later, a unidirectional rotational force is generated in the motor 9, which causes an offset voltage in the control system and reduces control accuracy. On the other hand, the other input terminal of the mixer 19 is given a focus error voltage (this voltage will be explained in detail later).Then, the mixer 19 increases the focus error voltage. An output mixed with the output signal of the oscillator 21 is generated, and this output is current-amplified by the current amplifier 24 and given to the DC reversible motor 9. As a result, the motor 9 generates vibration in synchronization with the output signal of the oscillator 21. , the focal length will be modulated.

In this case, the relationship between the focal length and the output of the detection circuit 13 when the focal length is modulated is as shown in FIG. That is, as shown in the figure, the focal length 1 is modulated at a constant frequency and the focal length is a.

When the waveform changes to three points b and c, the output waveforms of the detection circuit 13 become as shown in aI, bl, and cl in the figure.

To further explain this with reference to Fig. 8, the modulation waveform is shown in Fig.
(The frequency of this modulated wave is set in a range that the lens assembly 1 can sufficiently track, and is usually about 511z). Then, the output waveform a' of the detection circuit 13 corresponding to a in FIG. 7 is as shown in FIG. 1al, The output waveform C' corresponding to C is as shown in fc in the same figure, and the output waveform b' corresponding to b (the best point of focal length) is shown in FIG. Therefore, as is clear from FIG. 8, the phase of the output waveform of the detection circuit 13 is reversed when the focal length is in the CtM region and in the dwI region in FIG. 6, and when the focal length is at the best point. In this case, the output level of the detection circuit 13 is lowered, and its frequency is twice the modulation frequency.

Next, returning to FIG. 2, the output of the voltage amplifier 14 that amplifies the output of the detection circuit 13 exhibiting the characteristics described above is given to the bandpass filter 15.

Here, the filter 15 has a characteristic of passing around 5 Hz, which is illustrated in FIG. 9. In this case, the pass band is near 5 H2 and is twice this 10) 1
It is desirable to have sufficient attenuation near z.

The output of the bandpass filter 15 is sampled and held by a sampling and holding circuit 16. The sampling pulse at this time is the sampling pulse generator 2.
The sampling pulse generator 23 is triggered by the output of the delay circuit 22 which is triggered by the zero crossing point of the sine wave which is the output of the oscillator 21. The amount of delay is set so that the sampling pulse can be sampled at the point of change in the output of the edge bandpass filter 15 (the center point between zero and zero crosses).The relationship at this point is shown in FIG. In the figure, fal is the output waveform of the oscillator 21, (
b) is the output waveform of the delay circuit 22, (C) is the output of the sampling pulse generator 23, that is, the sampling pulse, l
dl is 1 - the output waveform of the filter 15 obtained from the output of the detection circuit 13 corresponding to the region C in FIG. 6, +
(Above) is the output waveform of the filter 15 obtained from the output of the detection circuit 13 corresponding to the dil range. The peak point of e) can be sampled. That is, the output of the sampling hold circuit 16
The phase of the output of the filter 15 with respect to the phase of the oscillator 21 is discriminated. Here, if) in FIG. 10 is the output of the detection circuit 13 at the best point (i.e., the 8th
This is the output waveform obtained by passing the substantially 10 Hz signal output shown in FIG. 9('b) through a filter 15 having the characteristics shown in FIG.

As a result, the output of the sampling and holding circuit 16 generates a focus error signal, that is, an error voltage, depending on the degree of focus, that is, front focus, rear focus, or focus, and when the focus is at its best, it becomes O■. (Figure 10(f)). This focus error voltage is then applied to mixer 19. Therefore, the focus error voltage is mixed with the modulation signal, the current is amplified by the current amplifier 24, and the amplified signal is supplied to the DC reversible motor 9. This causes vibration in the motor 9 and further modulates the focal length, but by making the loop system negative feedback, the focus error voltage is controlled to be zero, and as a result, the focal length is automatically adjusted. This will give you the best focal length.

By the way, if the focal length is constantly modulated in this way, it is conceivable that this will have an adverse effect on the video signal as visual flicker. Therefore, in the device of this example, the transistor 25 is used to turn the modulation on and off. That is, when the transistor 25 is on, the output of the mixer 19 is grounded and focus control is stopped. This is because there is no need to constantly perform focus control; focus control is applied only when the subject moves in the focal length direction, and the control loop is cut off after the subject is in focus to prevent image quality deterioration due to modulation. In this case, when the manual switch 27 is turned on, the output valley of the flip-flop 18 changes from "1" to "0" and the transistor 25 is turned off via the resistor 26. As a result, focus control is started, and when the focus becomes optimal, the output of the sampling and holding circuit 16 becomes O.
Beside the VJ. Then, this output is detected by the sensor 17, and if the output at this time falls within the threshold set for the sensor 17, the output of the sensor 17 becomes "1".
It switches from “0” to “0”. This causes flip-flop 1
8 is reset, the output Q changes from "0" to "1", and the transistor 25 is turned on. As a result, focus control is started after the switch 27 is pressed, and at the same time as the focus adjustment becomes optimal, the control loop is broken and the optimal state is maintained. After that, focus control will not be performed unless a command is given to the switch 27.

On the other hand, as described above with reference to FIG. 2, the composite synchronization signal 3o synchronized with the video signal 6 is sent to the vertical synchronization signal separator 28. A horizontal synchronizing signal separator 29 separates the signal into a vertical synchronizing signal and a horizontal synchronizing signal.

These separated signals are sent to wind pulse generators 31 and 3.
2 and each wind pulse is applied to an AND gate 33. Then, signals gated by wind pulses in the vertical and horizontal directions are generated in the AND gate 33. This signal is then applied to the analog gate 11 through the switch 34. Therefore, by turning on the switch 34, a part of the screen can be masked as shown in FIG. 11, and focus control can be performed only for the video signal indicated by the diagonal line, that is, a specific area within the screen is set as the focus target range. You can also do this.

Since the switch 34 can be easily operated from the outside at the operator's discretion, focus control for the entire screen can be performed by turning off the switch 34 as desired. As can be easily understood from the above, instead of arranging the analog gate 11 as shown in FIG. Even if it is provided so as to be inserted at an appropriate location in the path, the focus target region can be specified in the same way as in this example.

As mentioned above with reference to FIG. 2, it is obvious that if the circuit constants of the wind pulse generators 31 and 32 are designed to be variable or semi-fixed, the range to be focused within the screen can be selected from a wider range. It becomes possible. Therefore, to photograph a person in the center of the screen, you may choose to focus on a rectangular area in the center of the screen that includes the person's upper body, or you may choose to focus on a fast-moving subject such as a sports event by focusing on the entire screen. It is possible to select, as desired, to shoot as a target range, or to limit the focus range to a relatively small area during wide-angle shooting, such as shooting small birds flying between trees.

As described above, according to the device of this example, according to the subject,
Since it is possible to automatically obtain the best focal length for the focus target range selected as desired, this process requires much less effort than the conventional method of adjusting the focus each time according to the movement of the subject. Moreover, since a positive focus position can be obtained, a clear screen can always be obtained. Furthermore, with respect to flicker-like screen deterioration due to modulation, it is possible to prevent screen deterioration by automatically stopping modulation when the focus is controlled to the best condition.

In addition, since the vibrational displacement of the element of the 1M image optical system and the drive of the element for original focus adjustment are configured by the same moving means, the configuration is extremely simple.
Easy to downsize.

It should be noted that the present invention is not limited to the above-mentioned embodiments, but can be implemented with appropriate modifications within the scope without changing the gist. That is, in the above embodiments, a lens.

Although the lens, which is one element of the imaging optical system including the image pickup tube, is configured to be vibratedly displaced in the optical axis direction, it is possible to displace the lens, which is one element of the imaging optical system including the image pickup tube, in the optical axis direction. Alternatively, a solid-state image sensor or the like may be configured to cause vibrational displacement.

Further, the means for moving the elements of the imaging optical system is not limited to the DC motor, and it goes without saying that various driving sources having the same type of functions can be used.

〔Effect of the invention〕

According to the present invention, it is possible to select the range of focus within the screen as desired while maintaining the advantage of the conventional panosive force automatic focus control device that it can operate with low power.

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram showing the mechanical components of an embodiment of the present invention, Fig. 2 is a block diagram showing the electric circuit of the embodiment, and Figs. 3 to 11 explain the embodiment. This is a diagram for 1- Lens terra assembly 2-- Lens 3-
Image pickup tube 3a -Target 4- Incident light 5
------Video processor 6-----1 video signal
7, 8, 10---Gear 9-m-DC reversible motor 11 Analog gate 12--Differential circuit 13
Detection circuit 14 - Voltage amplifier 15 Band pass filter 16 - Sampling hold circuit 17 - Level sensor 18 - Flip-flop 19 - Mixer 20 -
- DC component removal circuit 21 - Oscillator 22 - Delay circuit 23 - Sampling pulse generator 24 Current amplifier 25 - Transistor 2 ()
Resistor 27 - Switch 2) +, 2
Signal separator 30-Synchronization signal 31.32
Wind pulse generator (3 and gate 34
For switch patents I11 Olympus Optical Industry Co., Ltd. Figure 1 Figure 3 Port;

Claims (1)

[Scope of Claims] An imaging optical system including elements such as an imaging lens and a photoelectric conversion means for imaging; and an area specifying means for specifying a portion related to the image pickup optical system; and an area specifying means for specifying a portion related to the image pickup optical system; vibrating means for modulating the relative position of the imaging photoelectric conversion means; high-frequency component extraction means for extracting a high frequency component of at least a portion related to the area specified by the area specifying means from the output signal of the imaging photoelectric conversion means; An automatic focus control device comprising means for moving a predetermined element in the imaging optical system in a direction that maximizes the output level of the area component extraction means.