JPS6345979A - Automatic focus controller - Google Patents

Abstract

PURPOSE:To simplify the constitution and to facilitate miniaturization by superimposing a focus error signal and an output signal of a signal generating means and displacing a prescribed element in an image pickup optical system vibratingly in an optical axis direction. CONSTITUTION:An output that an output signal of an oscillator 21 is mixed to a focus error voltage from a mixer 19 mis generated and is subjected to current amplification by a current amplifier 24 and given to a DC reversible motor 9. Thus, the motor 9 causes vibration synchronously with the output signal of the oscillator 21 to modulate the focus length. When a transistor (TR) 25 is turned on, then the output of the mixer 19 is earthed to stop focus control. Thus, only when the object is moved in the focus direction, the focus control is applied and after the focuses are coincident, the control loop is disconnected to prevent image quality deterioration due to modulation.

Description

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

[Conventional technology]

Devices for automatically focusing on a target subject in television cameras and the like are already known (for example, Japanese Utility Model Publication No. 40-26568). This is particularly effective under conditions where it is necessary to obtain a focused state in this manner. Among these types of devices, the method described in the above publication is generally called a passive method, and is configured to adjust the focus so as to maximize the high frequency component of the output of the imaging means. Unlike the active method, there is no need to specially install a projection means such as infrared light for focus detection, and it can operate with a relatively low power of -2°C, so it is especially suitable for small portable TV cameras, etc. Are suitable.

[Problem that the invention seeks to solve]

In the device described in Publication No. L, the movable lens of the camera is constantly vibrated and displaced by a focus fine adjustment device to detect the direction of defocus, and then perform two steps. (Thus, the direction of movement of the lens for focus adjustment is automatically identified.

Therefore, this device can quickly detect out-of-focus situations and direction when the subject repeatedly approaches and moves away from the camera. becomes possible.

However, in a 1-force distribution type device, the dynamic target 1; body G
In order to combine and adjust the 111 points, it is necessary to constantly change the separation in an oscillatory manner. In addition to the original focus mechanism for automatic focus adjustment, 1. Il, change the point distance vibrationally, \[! It is necessary to provide a special means for adjusting the focus (in the device described in Publication 1, a focusing fine mover provided separately from the servo motor), which complicates the configuration and reduces the size of the device. It also becomes an obstacle.

The present invention has been made in view of the above points, and it is an object of the present invention to provide an automatic focus control device of this type that is simple in structure and easy to downsize.

[Means and effects for solving the problems] In order to solve the above-mentioned problems, the present invention provides a non-life insurance optical system including elements such as an imaging lens and a photoelectric conversion means for imaging, and the above-mentioned photoelectric conversion means for imaging. a high-frequency component extracting means for extracting a high-frequency component from the output signal of the high-frequency component; a focus error signal forming means for forming a focus error signal corresponding to the degree of focus based on the output of the high-frequency component extracting means; a signal generating means for generating a repetitive signal; an I19 combination f stage for folding the focus error signal of the focus error signal forming means and the output signal of the signal generation means; and based on the output of the γIL combination stage 1. The predetermined base member 1 in the non-life insurance optical system is oscillatedly displaced by −1 in the optical axis direction, thereby forming an image in the imaging optical system a)).
Relative to the imaging surface of the photoelectric conversion means for recording the image (i7: rl!y) and the output of the mixing means (in the bar) - the output color of the component corresponding to the focus error signal Accordingly, it is provided with a means for moving the 19i constant correction in the imaging optical system. 11 displacements can be obtained.

〔Example〕

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

Reference numeral 1 designates a camera lens assembly, and an imaging tube (3) serving as a photoelectric conversion stage (F) for imaging is disposed on the optical axis of an imaging lens (2) of this assembly (1), and human power light (4) given through the lens (2) is transferred to the imaging tube. The image is formed on target 3a of No. 3.

1-Note 1 A damage optical system according to the present invention is configured including the Kamagawa lens 2 and the image pickup tube 3. The target 3a is connected to a video processor 5, and the output from the target 3a is subjected to signal processing and output as a video signal 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 the output side of this analog gate 11 includes a differentiation circuit 12, a detection circuit 13,
The voltage amplifier 14, the bandpass filter 15, and the sampling hold circuit 16 are connected in a v1 series in the above-mentioned order. The sampling hold circuit 16 is connected to the level sensor 17
It is connected to the R terminal of the flip-flop 18 via the R terminal of the flip-flop 18, and also to one input terminal of the mixer 19. A DC component removal circuit 20 is connected to the other input terminal of the mixer 19.
The output terminal of the oscillator 21 is connected through the oscillator 21. 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 has its base connected to the resistor of the flip-flop 18 through a resistor 26. 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, 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. Further, each output side of these synchronizing signal separators 28 and 29 is connected to an AND gate 3 via a wind pulse generator 3L32.
It is connected to the input side of 3. The output side of this AND gate 33 is connected to the analog gate 11 via a switch 34.

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, ta
+=9- is the waveform of the video signal, the peak) is the output waveform of the differentiating circuit 12, I
C) is the output waveform of the detection circuit 13. Further, the relationship between the output of the detection circuit 13 and the focal length is shown in FIG. As already explained, the output voltage of the detection circuit 13 reaches the maximum level in the state of best focus. In this case, if the focal length is modulated by a modulation signal of a constant frequency by displacing a predetermined element in the imaging optical system such as a lens, for example, in the focal state at point A in FIG.
When modulation is applied in the sinusoidal waveform state shown in , the detection circuit 13 produces an output similar to the above modulated waveform a as shown in a'.

In particular, in the present invention, this focal length modulation is achieved by rotating the DC reversible motor 9, which is the same as the one for focal length control described above with reference to FIG. For example, it is configured to perform this by applying it to the lens 2. This vibration is obtained in the following way. That is, oscillator 2
1 generates an output that becomes the original signal of the vibration frequency. This output is supplied to one input terminal of the mixer 19 via the DC component removal circuit 20. Here, the DC component removal circuit 20 includes a capacitor and removes the DC component of the oscillator 21 and provides only the modulated signal component to the mixer 19. The reason for this is that when direct immersion 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 to be generated in the control system, reducing control accuracy. It is from. Meanwhile, mixer 1! A focus error voltage (this voltage will be explained in detail later) is applied to the other input terminal of -ζ. Then, the mixer 19 generates an output in which the output signal of the oscillator 21 is mixed with the focus error voltage.
This output is current-amplified by a current amplifier 24 and applied to the DC reversible motor 9. This causes the motor 9 to generate an oscillator 21
Pisillation occurs in synchronization with the output signal of the lens, and the focal length is modulated.

In this case, the relationship between the focal length and the output of the detection circuit 13 when the focal point V distance is modulated is as shown in FIG.

That is, as shown in the figure, the focal length 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 a', t/d, and d in the figure. To further explain this with reference to FIG. 8, the modulation waveform is shown in FIG.
Then, the output waveform a' of the detection circuit 13 corresponding to a in FIG. 7 is +al in the figure, and the output waveform d corresponding to C in the figure is (c
), and the output waveform b' corresponding to b (the best point of focal length) is as 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 CffI region and in the d 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.

In general, the filter 15 has a characteristic of passing the light mainly at 511z, which is illustrated in FIG. 9. In this case, the pass band is around 5 Hz, which is twice this, 1011
It is desirable to have sufficient attenuation near z.

The output of the bandpass filter 15 is sampled and held by a sampling hold circuit 16. The limp ring pulse at this time is generated by the sampling pulse generator 23, which is triggered by the output of the delay circuit 22 that is triggered by the zero-crossing point of the sine wave that is the output of the oscillator 21. Ru. In this case, the delay amount of the delay circuit 22 is set so that the sampling pulse can sample the change point of the output of the Hashi 1' pass filter 15 (the center point between zero crosses). The current relationship is shown in FIG. In the figure (al is the output waveform of the oscillator 21, (b) is the output waveform of the delay circuit 22, (C) is the output of the limp ring pulse generator 23, that is, the sampling pulse, and fdl is the c j J (area The detection circuit 13 corresponds to
(e) is the output waveform of the filter 15 obtained from the output of the detection circuit 13 corresponding to the d fil region, and as can be seen from the figure, the sampling pulse fc) The output of the filter 15, that is, the peak point of (dl or (e)) can be sampled. That is, the sampling hold circuit 16
With the output of , when the phase of the oscillator 21 is referenced,
The phase of the output of filter 15 will be discriminated. Here, ff in FIG. 10 is the output of the detection circuit 13 at the best point (i.e., substantially 1011z shown in FIG. 8 (bl)
This is the output waveform obtained by passing the signal output (signal output) through the filter 15 having the characteristics shown in FIG.
Therefore, the output voltage becomes Ov.

As a result, a focus error signal or error voltage is generated at the output of the sampling and holding circuit 16 depending on the degree of focus, that is, front focus or rear focus, and when the focus is at its best, it becomes Ov ( Figure 10(f)). This focus error voltage is then input to the mixer 19. Therefore, the focus error voltage is mixed with the modulation signal, the current is amplified by the current amplifier 24, and the current is supplied to the l\1' flow 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 zero, and as a result, the optimal This results in a focal length of .

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 to stop focus control. °This is because there is no need to perform focus control all the time; focus control is applied only when the subject moves in the focal length direction, and the focus is matched. The control loop is then cut off to prevent image quality deterioration due to modulation. In this case, ■-Dosuinochi 2
7 is turned on, the output of the flip-flop 18 becomes “1”.
” to “0” and the transistor 25 is connected via the resistor 26.
is turned off. As a result, focus control is started, and when the focus becomes optimal, the output of the sampling and holding circuit 16 becomes near O■. This output is then detected by the sensor 17, and when the output at this time falls within the threshold set for the sensor 17, the output of the sensor 17 switches from "1" to "0". As a result, the flip-flop 18 is reset and 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 30 synchronized with the video signal 6 is transmitted 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 for only the video signal shown in the diagonal line, that is, a specific area within the screen is 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 description, instead of arranging the analog gate 11 as shown in FIG. Even if it is inserted at an appropriate location in the signal path, the focus target area can be specified in the same way as in this example.

As mentioned above with reference to FIG. 2, it goes without saying that if the circuit constants of the wind pulse generators 31 and 32 are designed to be variable or semi-fixed, the range of focus within the screen can be made wider. can be selected. 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. You can always get a clear screen because you can get a precise focus position. 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 elements of the imaging optical system and the drive of the elements for original focus adjustment are performed by means of rotational movement, the configuration is extremely simple and miniaturization is easy. .

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 vibrate and displace.

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, while maintaining the advantage of the conventional passive autofocus control device that it can operate with low power, a means for applying minute vibrational displacement to the elements of the imaging optical system and the original focus adjustment are provided. Since the same device can be used as the means for applying the displacement for the purpose, the structure is extremely simple and it is easy to downsize.

[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-----1--Lens assembly 2-------
Lens 3 ------- One image pickup tube 3 a ---- Target 4 ------- Individual emitted light 5 ----
------Video processor 6-----1 video 1 word
7, 8, 10---Ikko Gear 9------
DC reversible motor 11 --- Analog gate 12 --- One thorough circuit 13 --- Detection circuit 14 --- One --- Voltage amplifier 15 ---- Band pass filter 16 --- Sampling hold circuit 17 -Level sensor 1 B--1--Flip-flop 19--1 Mixer 20 DC component removal circuit 21--1--
Oscillator 22---Delay circuit

Claims (1)

[Scope of Claims] An imaging optical system including elements such as an imaging lens and an imaging photoelectric conversion means; a high frequency component extraction means for extracting a high frequency component from an output signal of the imaging photoelectric conversion means; a focus error signal forming means for forming a focus error signal according to the degree of focus based on the output of the area component extracting means; a signal generating means for generating a repetitive signal of a predetermined frequency; and a focal point of the focus error signal forming means. a mixing means for superimposing an error signal and an output signal of the signal generating means; and a predetermined element in the imaging optical system is vibrably displaced in the optical axis direction based on the output of the mixing means, thereby controlling the imaging optical system. The imaging optical system modulates the relative position between the imaging position in the system and the imaging surface of the imaging photoelectric conversion means, and also modulates the output level of the component corresponding to the focus error signal in the output signal of the mixing means. an automatic focus control device comprising means for moving a predetermined element therein.