JPH0773341B2 - Automatic focusing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focusing device for video cameras. 2. Description of the Related Art Conventionally, as an automatic focusing device for a video camera, a fineness of a screen is detected by a high frequency component in a video signal, and a focusing ring of a lens (hereinafter referred to as a helicoid) is used to maximize the fineness. A so-called hill-climbing control is known in which the rotation control of the This method is NHK
Technical Research Report Sho 40. Volume 17, Issue 1 Issue 86 2
It is described in detail on page 1 as "Automatic focus adjustment of TV camera by mountain climbing servo system" by Ishida et al.
This method will be briefly described below with reference to FIGS. FIG. 1 is a block diagram showing a configuration of an automatic focusing device (hereinafter referred to as an AF device) by a hill climbing method. 1 is a lens system, 2 is a camera circuit, 3 is a video signal output terminal, 4 is a high-pass filter, 5 is a detector,
6 is a difference hold circuit, 7 is a motor drive circuit, and 8 is a motor for rotating the helicoid of the lens system 1. The operation of the configuration of FIG. 1 will be described below with reference to the characteristic diagram of FIG. From the subject (not shown) to the lens system 1
The optical information incident on is converted into an electric signal by the camera circuit 2 and output to the terminal 3 as a video signal. Only the high frequency component of the video signal is extracted by the high pass filter 4, detected by the wave detector 5, and then appears at the terminal 51. Voltage corresponding to high frequency component of video signal (hereinafter referred to as focus voltage)
Corresponds to the definition of the captured image, so that the focus voltage appearing at the terminal 51 as shown in FIG. 2 is as long as the helicoid position (A) of the lens system 1 matches the distance to the subject. It becomes maximum and decreases as the helicoid position of the lens system 1 deviates from the position A. The helicoid position is controlled by some means, and the terminal 51
If the position of the helicoid is controlled so that the focus voltage supplied to the lens is maximized, the focusing is automatically performed. The differential hold circuit 6 has a terminal 5 as shown in FIG.
The focus voltage appearing in No. 1 is sampled and held at fixed time intervals, and a positive voltage is generated when the focus voltage increases with time, and a negative voltage is generated when the focus voltage decreases with time. If the output voltage of the differential hold circuit 6 appearing at the terminal 61 is positive, the motor drive circuit 7 moves the motor 8 forward, for example, to move the helicoid position in the forward direction, and the output voltage is negative. Then motor 8
Reverse to move the helicoid position in the opposite direction. The output voltage of the differential hold circuit 6 shown in FIG. 2 shows the case where the helicoid is rotated from the infinity direction to the infinity direction, but the same applies when the helicoid is rotated from the infinity direction to the infinity direction. Easily understood. In this way, the control system for controlling the helicoid position of the motor 8 climbs the mountain formed by the focus voltage of the mountain climbing circuit 9 by the output voltage of the differential hold circuit 6, and finally this mountain. Focusing is automatically achieved by reaching steady state with small vibrations at the top. The above is an automatic focusing device for a video camera by the hill climbing method. Although the above-mentioned device has sufficient performance as an automatic focusing device, it has the following drawbacks. The first drawback is due to the characteristics of the lens system 1. The lens system has a front-lens rotating focusing mechanism which is mainly used at present, that is, the lens system is arranged at a position close to an object. In the system for moving the position of the objective lens to perform focusing, when the helicoid position is moved for focusing, the lens system 1
The focal length itself of the lens system 1 slightly changes with the in-focus distance. In other words, the hill climbing method is a method in which the focus signal increases and decreases by feeding back, so that the helicoid position oscillates with the top of the mountain as the center of gravity during focusing.
The focal length of the lens system 1 is also slightly vibrating for the above reason. Since the change in the focal length of the lens system 1 directly means the change in the angle of view of the image of the lens system 1, that is, the change in the magnification of the taken image, the image taken by the hill-climbing automatic focusing device is always the same. The size of the image is vibrating. The vibration of the size of this image has a steep slope of the mountain due to the focus signal in the case where the lens system 1 has a shallow depth of field such as a small aperture value and a high zoom magnification. The amplitude of the vibration is small, which is almost unnoticeable, but when the depth of field is deep, such as when the aperture value of the lens system 1 is large and the zoom magnification is low, the slope of the mountain due to the focus signal is very broad. Therefore, the amplitude of the vibration of the helicoid becomes large, and the size of the captured image changes by several percent or more in accordance with the vibration at the helicoid position. The second drawback is that the power consumption is large, though not as fatal as the above-mentioned first drawback. That is, in this method, since the helicoid needs to be constantly rotating, the motor 8 for driving the helicoid constantly consumes power, and in the case of a camera such as a portable video camera in which power supply is a problem. Then it becomes a big fault. An object of the present invention is to eliminate the above-mentioned conventional drawbacks and to provide an automatic focusing device which does not cause a noticeable vibration of the size of a captured image at the time of focusing. In the present invention, the depth of field of the lens at that time is calculated using the aperture value and the focal length (zoom magnification) of the lens, and the depth of field is taken into consideration. To calculate the helicoid stop position that can cover from close range to infinity (hereinafter referred to as Haken point), and to find out which of these stop positions is the in-focus position. Using the climbing method, once the focus is achieved, the closed loop of the mountain climber is released and at the same time the helicoid is stopped at a predetermined position (Haken point) closest to the mountain top. And
When the focus is out of focus for some reason, the mountain climbing closed loop is closed again to restart the mountain climbing type focusing function. As a result, an unnecessary vibration phenomenon in the focused state can be prevented, and when the photographing state changes and the lens aperture value and the focal length need to be adjusted, the automatic focusing function can be performed again. I tried to work. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described in detail below with reference to FIGS. FIG. 3 is a block diagram showing the configuration of an embodiment of the automatic focusing device according to the present invention. 1, 2, 8, 9, 51, and 61 output the same lens system, camera circuit, motor, mountain climbing circuit, and focus voltage as those used in the conventional automatic focusing circuit described with reference to FIG. And a terminal for outputting the output voltage of the differential hold circuit. Reference numerals 11 to 14 respectively convert the focal voltage, the focal length information of the lens system 1, the focal length information of the lens system 1, the aperture value information of the lens system 1, and the helicoid position information of the lens system 1 into digital values. Is an A / D converter for. 15 is a Haken point calculation circuit, 16 is a Haken point memory, 17, 19, 21, 23 are comparison circuits,
18 is a stop Haken point memory, 20 is a Haken point number memory, 22 is a focus voltage memory, 24 and 25 are sum circuits, 26 is a counter, 27 is a first helicoid position memory, 28 is a second helicoid position memory, and 29 is an average. A value circuit, 30 is a motor drive circuit, and 31 is an electronic switch. The motor drive circuit 30 operates in the same manner as the conventional motor drive circuit 7 in FIG. 1 when a signal is applied to the C side input line, but stops the motor 8 when a signal is applied to the D side input line. Have. Before describing the automatic focusing operation in the present invention, the Haken points will be described. The Haken point is a predetermined stop position of the helicoid that can cover from a close-up distance to infinity (hereinafter referred to as ∞) in consideration of the depth of field of the lens system 1 at that time. Equation 1] can be used for calculation. [Equation 1] However, i is a positive integer ... [Equation 1], where R
i is the i-th Haken point counted from the infinity ∞ side,
ρ is the diameter of the permissible circle of confusion of the captured image, f is the focal length of the lens 1, and F is the aperture value of the lens 1. Further, the number N of required Haken points is N, where Rmin is the close range in which the lens 1 can be imaged.
Since the second Haken point should be equal to or smaller than Rmin, it can be calculated by the following [Equation 2]. [Equation 2] For example, as the lens 1, the focal length f = 5
0mm, aperture value F = 1.8, close range Rmin = 1m,
When the diameter of the permissible circle of confusion is ρ = 40 μm, [Equation 2]
Therefore, the number of Haken points N is 18, and from [Equation 1], the position Ri of each Haken point is R ₁ = 34.72 m, R
_{2 = 11.57m, R 3 = 6.94m} , ......... R 18 = 0.9
It is 9m. That is, in this case, the position of the helicoid is set to the Haken point R ₁ ~
If you select the most suitable one of R ₁₈ , you can shoot with a certain focus. The above is the explanation of Haken point. In the present invention, the conventional mountain climbing method is used to find the optimum Haken point. The operation will be described below. Information on the aperture value F and the information on the focal length f of the lens system 1 are A / D converted by the A / D converters 11 and 12, respectively.
It is D-converted into a digital code, which is input to the Haken point calculation circuit 15. The Haken point calculation circuit 15 calculates the Haken point number N and Haken point positions R1 to RN based on the above [Equation 1] and [Equation 2], stores the Haken point number in the Haken point number memory 20, and stores each Haken point number. The point position is stored in the Haken point memory 16. The operation of the configuration shown in FIG. 3 will be described below in three stages. (First stage) The halken point position where the helicoid of the lens system 1 should stop is determined. (Second step) The helicoid is controlled to the Haken point position determined in the first step and stopped. (Third step) It is detected again whether or not the focusing operation is necessary, and the focusing operation is started again. First, the first stage will be described. The first stage is divided into the following two small stages. (Step 1.1) The number of Haken points and each Haken point position are calculated and stored from the focal length f and the aperture value F of the lens system 1 by the above [Equation 1] and [Equation 2]. (Step 1.2) The in-focus helicoid position is obtained by the mountain climbing method which is almost the same as the conventional one, and then the optimum Haken point position is obtained. In step 1.1, the information on the focal length f of the lens 1 and the information on the aperture value F are obtained from the A / D converter 1 respectively.
It is converted into a digital value at 1 and 12 and input to the Haken point calculation circuit 15. The Haken point calculation circuit 15 calculates the Haken point number and each Haken point position R _{1 to} Rn by the above [Mathematical Expression 1] and [Mathematical Expression 2], and stores them in the Haken point number memory 20 and the Haken point memory 16, respectively. At the 1.2th stage, the electronic switch 31 is on the A side, so that the focusing operation is performed by almost the same operation as the conventional mountain climbing method described with reference to FIG. After the reverse rotation (up to 3 times), the electronic switch 31 is on the B side and the mountain climbing loop is opened. This operation will be described with reference to FIG. FIG. 6A shows the peak of the focus voltage, where the helicoid operation start point is h ₁ and the new helicoid position is h ₂ . This state occurs, for example, when the helicoid at the position h ₁ moves to the position h ₂ . At the start of mountain climbing operation, when the motor 8 starts moving the helicoid in the direction of climbing the mountain as shown in FIG. 4B, the locus traced by the helicoid position climbs the mountain as it is, and the focus position h ₂ , the position h ₂ is passed, the output signal of the terminal 61 is inverted, and the in-focus position h ₂ is moved in a reverse direction from the position h ₃ which is a little too far, and the position h ₂ is passed again and the position h is passed again. _{Use 4} to move in the opposite direction. If the hill climbing loop is closed as it is, the helicoid continues to oscillate between the positions h ₃ and h _{4 as in} the conventional example. However, the fact that the helicoid position has reached the vicinity of the in-focus position h ₂ is known by detecting the above-mentioned two reversals. Therefore, in the configuration of FIG. 3, the counter 26 calculates the reverse rotation signal which is the output signal of the terminal 61, and the information of the helicoid position h ₃ at the time of the first reverse rotation is stored in the first helicoid position memory 27 and the second time. Information on the helicoid position h ₄ at the time of reverse rotation is stored in the second helicoid position memory 28, and at the same time as the second reverse rotation, the sum circuit 2
The electronic switch 31 is set to the B side via 5 to open the mountain climbing loop. Further, when the motor 8 at the start of the mountain climbing operation began moving the helicoid in the direction of descending a mountain as shown in FIG. 4 (c), helicoid trajectory drawing before reaching the focus position h ₂ Position h before it overlaps the trajectory of (b)
_The motor 8 needs to reverse once from ₁ to the position h _{5 to the} position h ₂ . In this case, the determination circuit 32 knows that the output voltage of the terminal 61 has decreased at the start of the mountain climbing operation and is descending the mountain, and resets the contents of the counter 26 after the first inversion, and then the second In order to prepare for the third reverse rotation, also in the case of FIG. 4C, the helicoid position is near the in-focus position h ₂ by the second and third reverse rotations as in the case of FIG. 4B. When it is reached, the hill climbing loop is released. Now, when the content of the counter 26 becomes the value 2 and the hill climbing loop is opened, the content of the Haken point memory 16 is sequentially input to the comparison circuit 17,
The contents of the first helicoid position memory 27 and the second helicoid position memory 28 are compared with a value averaged by the average value circuit 29, and the contents of the Haken point memory 16 closest to the average value are stored in the stopped Haken point memory 18. It Next, the comparison circuit 19 controls the helicoid position of the lens system 1 via the B side of the electronic switch 31, the motor drive circuit 30, and the motor 8 and inputs the contents of the stop halken point memory 18 and A / D. The information on the helicoid position of the lens system 1 which is the output of the converter 14 is made to match, and when they match, a signal is supplied to the motor drive circuit 30 through the input line on the D side, and the second stage is ended. Next, a description will be given of the case where it is necessary to refocus again due to a change in the distance between the object and the camera in the third stage and a change in the aperture value F focal length f of the lens system 1. Aperture value F and focal length f of the lens system 1
Is changed, if the contents of the Haken point number memory 20 input to the comparison circuit 21 and the new Haken point number input from the Haken point calculation circuit 15 are the same, it is not necessary to perform the focusing operation again. However, when they are different, the comparison circuit 21 performs the focusing operation again, so that the electronic switch 31 is connected to the A side via the summing circuits 24 and 25, the determination circuit 32 resets the counter 26, and the comparison is started from the first stage. Start the focusing operation. When the distance between the subject and the camera changes, the focus voltage output from the A / D converter 13 input to the comparison circuit 23 and the output voltage of the focus voltage memory 22 are different from each other. When the value exceeds a predetermined value, the comparison circuit 23 performs the focusing operation again, so that the sum circuits 24 and 25 are added.
The electronic switch 31 is connected to the A side via the, and the determination circuit 32 resets the counter 26 to start the focusing operation from the first stage. In any of the above cases, after the motor 8 is rotated, the initial value of the helicoid position is not the position h ₁ as described with reference to FIG. 4, but another value as shown in FIG.
A new focal point can be reached through a process similar to that described with. In the above description, the focusing operation is not described when the helicoid is at infinity or infinity during operation, but in this case, the motor 8 is unconditionally reversed. To continue the operation from. It has been explained that the refocusing operation when the distance between the subject and the lens changes after focusing is started immediately if the focus voltage memory and the focus voltage at that time are different. For example, it has been found that it is preferable to perform the refocusing operation only after the difference between the two is about 10% to 20%. Further, in the description of the embodiment of the present invention, the number of Haken points is set to the minimum number for covering the depth of field without any gap, and the position of each Haken point is selected so as to correspond to the number of Haken points. However, the number of Haken points used in the present invention may be any number as long as it is equal to or more than the above-mentioned minimum number, and the Haken point position in this case is only required as long as the depths of field covered by the adjacent Haken points overlap each other. It goes without saying that it is good. Furthermore, in the special case where the number of halken points calculated by the halken point calculating circuit 15 in FIG. 3 is 1, the helicoid may be unconditionally moved to the halken point without performing the hill climbing operation. According to the present invention, after focusing, the helicoid can be completely stopped until it becomes necessary to perform the focusing operation again due to the movement of the subject or the movement of the camera. It is possible to capture a good image without vibration of the film angle caused by the vibration of the helicoid that existed in the mountain climbing method.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a conventional mountain climbing type automatic focusing device. FIG. 2 is a waveform diagram for explaining the operation of the configuration of FIG. FIG. 3 is a block diagram showing an embodiment of an automatic focusing device according to the present invention. FIG. 4 is a waveform diagram for explaining the operation of the configuration of FIG. [Explanation of Codes] 1 ... Lens system, 2 ... Camera circuit (photoelectric conversion means), 7 ... Motor drive circuit, 8 ... Motor, 9 ... Mountain climbing circuit (focus voltage detection means), 22 ... Focus voltage memory (storage means) ), 23 ... comparison circuit, 30 ... motor drive circuit, 31 ... electronic switch (switch means).

Claims (1)

[Claims] 1. An image pickup means for converting light from a subject into a video signal; a lens provided between the subject and the image pickup means, movable in the optical axis direction; and a motor for moving the lens position of the lens in the optical axis direction, A focus having a characteristic that a high frequency component of the video signal output from the image pickup means is extracted, becomes maximum at a focusing lens position in the middle of the moving range of the lens, and decreases as the lens moves away from the focusing lens position. When performing an automatic focusing operation by a feedback loop consisting of a focus voltage generating unit that generates a voltage and a motor driving unit that controls the rotation of the motor so that the lens moves in the direction in which the focus voltage increases. In, when the focus position detection means for detecting that the lens has reached the focus lens position, and the detection by the focus position detection means, A lens setting means for opening the feedback loop to stop the movement of the lens, a storage means for storing the focus voltage when the lens is stopped, a value stored in the storage means, and a sequential input And a comparing means for generating an output signal for closing the feedback loop when the difference between the two exceeds a predetermined value of 10% or more. An automatic focusing device, characterized in that the vibration of the lens caused near the position of the focusing lens is prevented by the automatic focusing operation by the feedback loop, and the automatic focusing operation is restarted in response to the change of the photographing condition.