JPH02210977A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To eliminate vibration of a picture angle by obtaining a harken point position where a helicoid of a lens system is to be stopped and controlling the helicoid to the obtained harken point position. CONSTITUTION:A herken point calculation circuit 15 calculates a harken point number and a harken point location from the information of an aperture and focus of a lens system 1. A comparator circuit 19 controls a helicoid location of the system 1 via a B position of an electronic switch 31, a motor drive circuit 30 and a motor 8 to make the content of an inputted stop harken point memory 18 with the information of a helicoid position of the system 1. Moreover, when a distance between an object and a camera is changed, the switch 31 is thrown to the position A via sum circuits 24, 25 to allow focusing of the comparator circuit 23, a discrimination circuit 32 sets a counter 26 to start the focusing.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic focusing device for a video camera.

Traditionally, automatic focusing devices for video cameras detect the definition of the screen based on high-frequency components in the video signal, and then control the rotation of the lens focusing ring (hereinafter referred to as helicoid) to maximize the definition. So-called mountain climbing control is known.

This method was introduced in the NHK technical research report in 1974. Volume 17.

No. 1, Volume 86, page 21, it is described in detail by Ishida et al. as ``Automatic focus adjustment of television camera using mountain-climbing servo method'', but this method will be briefly explained below using Figures 1 and 2. explain.

Figure 1 shows a hill-climbing automatic focusing device (hereinafter referred to as A).
FIG. 2 is a block diagram showing the configuration of an F device. 1 is a lens system, 2 is a camera circuit, 3 is a video signal output terminal, 4 is a bypass filter, 5 is a detector, 6 is a differential hold circuit, 7 is a motor movement circuit, 8 is a helicoid of lens system 1 This is a motor for rotation.

The operation of the configuration shown in FIG. 1 will be explained below using the characteristic diagram shown in FIG. 2.

Optical information incident on the lens system 1 from a subject (not shown) is converted into an electrical signal by the camera circuit 2 and sent to the terminal 3.
is output as a video signal. Only high frequency components of the video signal are extracted by a bypass filter 4, detected by a detector 5, and then applied to a terminal 51. The voltage corresponding to the high-frequency component of the video signal (hereinafter referred to as focal voltage) corresponds to the definition of the captured image, so as shown in FIG.
The focal voltage that appears at the helicoid position of lens system 1 (assumed MCA) is maximum if it matches the distance to the subject, and as the helicoid position of lens system 1 deviates from the above position A, descend. If the helicoid position is controlled by some means such that the focusing voltage supplied to the terminal 51 is maximized, focusing will be performed automatically.

As shown in FIG. 2, the differential hold circuit 6 samples and holds the focal voltage applied to the terminal 51 at fixed time intervals.
The motor drive circuit 7 is a circuit that generates a positive voltage when the focal voltage increases over time, and a negative voltage when the focal voltage decreases over time.
1, if the output voltage of the differential hold circuit N6 is positive, the motor 8 is rotated in the forward direction to move the helicoid position in the forward direction, and if the same output voltage is negative, the motor 8 is rotated in the reverse direction to move the helicoid position. , move the id position in the opposite direction.

The output voltage of the differential hold circuit 6 shown in FIG. 2 is shown when the helicoid is rotated from close to infinity, but the same applies when the helicoid is rotated from infinity to close. This is easily understood.

In this way, the control system that controls the helicoid position of the motor 8 climbs the mountain created by the focal voltage of the mountain climbing circuit 9 using the output voltage of the differential hold circuit 6, and finally reaches the top of this mountain. By vibrating in small increments and reaching a steady state, the focus is automatically adjusted.

The above is an automatic focusing device for a video camera using the mountain climbing method.

Although the above-mentioned device has sufficient performance as an automatic focusing device, it has the following drawbacks.

The first drawback lies in the characteristics of the lens system 1, which is currently mainly used in lens systems having a front lens rotation type focusing mechanism.

In other words, in a system that focuses by moving the position of an objective lens placed close to the subject, when the helicoid position is moved for focusing, the focal length of the lens system 1 changes as well as the focusing distance of the lens system 1. The distance itself will change slightly. In other words, in the mountain climbing method, the helicoid position vibrates and stays at the top of the mountain by feeding back the increase and decrease of the focus signal, so even during one focusing, the helicoid position oscillates with the center of gravity at the top of the mountain, and the lens system The focal length of 1 also oscillates, albeit slightly, for the reasons mentioned above. A change in the focal length of the lens system 1 directly means a change in the angle of view of the lens system 1, that is, a change in the magnification of the captured image. This means that the size of the image is oscillating. This fluctuation in image size is caused by the steep slope of the mountain caused by the focus signal when shooting when the depth of field of the lens system 1 is shallow, such as when the aperture value is small and the zoom magnification is high. The amplitude of the vibration is also small and hardly noticeable, but when the depth of field is deep, such as when the aperture value of lens system 1 is large and the zoom magnification is low, the slope of the mountain caused by the focus signal becomes very noticeable. As a result, the amplitude of the helicoid's vibration increases, and the size of the captured image changes by several percent or more in accordance with the vibration of the helicoid's position.

The second drawback is that the power consumption is large, although the first drawback described above is not fatal. In other words, this method requires the helicoid to be constantly rotating, so
The motor 8 for driving the helicoid constantly consumes power, which is a major drawback in cameras where power supply is a problem, such as a portable video camera.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned conventional drawbacks and to provide an automatic focusing device that does not cause noticeable vibration in the size of a photographed image during focusing.

The drawback of conventional autofocusing devices using the mountain climbing method is that they always control the helicoid. Therefore, when the depth of field is large and the subject is virtually in focus no matter where the helicoid is located, the shape of the mountain becomes very broad, imitating the vibrations of a large helicoid.

In the present invention, the depth of field of the lens at that point is calculated using the aperture value and focal length (zoom magnification) of the lens,
Considering the depth of field, calculate the stopping positions of the helicoid that covers from close range to infinity (hereinafter referred to as Birken points), and determine which of these stopping positions is the in-focus position. Use the mountain climbing method only to find the mountain peak, and once you have focused, you can open the mountain climbing closed loop and at the same time move the helicoid to a predetermined position closest to the mountain top! (Birken point). When the camera goes out of focus for some reason, the mountain climbing closed loop is closed again, and the mountain climbing method focusing function is restarted.

Hereinafter, one embodiment of the present invention will be described in detail with reference to FIGS. 3 and 4.

FIG. 3 is a block diagram showing the configuration of an embodiment of an automatic focusing device according to the present invention.

1. 2, 8, 9, 51, and 61 are the same lens system, camera circuit, and motor as used in the conventional automatic focusing circuit explained using FIG. 1, respectively.

These are the terminal to which the mountain climbing circuit, the focal voltage is output, and the terminal to which the output voltage of the differential hold circuit is output.

11 to 14 are A/D converters for converting the focal voltage, information on the focal length of the lens system 1, information on the aperture value of the lens system 1, and information on the helicoid position of the lens system 1 into digital values, respectively. be. 15 is a Birken point calculation circuit, 16 is a Birken point memory, 1
7,19゜21.23 is a comparison circuit, 18 is a stop Birken point memory, 20 is a Birken point number memory, 2
2 is a focal voltage memory, 24.25 is a summation circuit, 26 is a counter, and 27 is a first helicoid position memory.

28 is a second helicoid position memory, 29 is an average value circuit,
30 is a motor drive circuit, and 31 is an electronic switch. The motor braking circuit 30 operates in the same way as the conventional motor drive circuit 7 shown in FIG. 1 when a signal is applied to the input line on the C side, but stops the motor 8 when a signal is applied to the input line on the D side. Has a function.

Before explaining the automatic focusing operation in the present invention, the Birken point will be explained.

The Birken point is a predetermined stopping position of the helicoid that covers the distance from close range to infinity (hereinafter referred to as Q) considering the depth of field of the lens system 1 at that point, and is described in (1) below. It can be calculated using the formula.

R1=1my1-pF (2i-1) However, i is a positive integer...(
1) where Ri is the i-th Birken point counted from the infinity ψ side, ρ is the diameter of the permissible circle of confusion of the photographed image, f is the focal length of the lens 1, and F is the aperture value of the lens 1.

Also, the number N of Birken points required is 1 for each lens.
If the closest distance that can be photographed is Ra1n, the Nth Birken point should be equal to or smaller than Rlin, so it can be calculated using the following equation (2).

lf”I N≧−・−・−1−・・・・・・・・・(2) Formula 2% For example, as lens 1, focal length 11f=50■, aperture value F=1.8, close distance When using 111Rmin=1m and the diameter of the permissible circle of confusion as ρ=40μm, the number of Birken points N is 18 from equation (2), and the position Ri of each Birken point from equation (1) is R□= 34.72m,
R,:=11.57m, R,=6.94m,...
-R,,=0°99m. That is, in this case, no matter what distance the subject is, if the helicoid position is selected at the optimal one from the Birken Point position to R0, it is possible to take a picture in a predetermined focus. This is the explanation of Birken Point.

In the present invention, a conventional mountain climbing method is used to find the optimal Birken point. The operation will be explained below.

Information on the aperture value F and information on the focal length f of the lens system I are A/D converted by A/D converters 11 and 12, respectively, into digital codes, and both are input to the Birken point calculation circuit 15. The Birken point calculation circuit 15 calculates the Birken point number N and Birken point positions R1 to RN based on the above-mentioned formulas (1) and (2), and stores the Birken point number in the Birken point number memory. 2o, and each Birken point position is stored in the Birken point memory 16.

The operation of the configuration shown in FIG. 3 will be explained in the following three steps.

(First step) Find the Birken point position where the helicoid of the lens system 1 should stop.

(Second stage) Control the helicoid to the Birken point position determined in the first stage and stop.

(Third stage) It is detected whether or not there is a need to perform a focusing operation again, and the focusing operation is started again.

First, the first stage will be explained. The first stage is divided into the following two substages.

(Step 1.1) The number of Birken points and the position of each Birken point are calculated from the focal length f and the aperture value F of the lens system 1 using equations (1) and (2), and are stored.

(Step 1.2) The focusing helicoid position is determined using a mountain climbing method similar to the conventional method, and then the optimal Birken point position is determined.

In step 1.1, the information on the focal length @f and the aperture value F of the lens 1 are each converted into digital values by the A/D converter 11.12, and the information is converted into a digital value by the Birken point calculation circuit 15.
is input. The Birken point calculation circuit 15 is configured as described above (
The number N of Birken points and each Birken point position R1 to Rn are calculated using equations 1) and (2), and are stored in the Birken point number memory 2o and the Birken point memory 16, respectively.

In the 1st and 2nd stages, the electronic switch 31 is on the A side, so the focusing operation is performed in almost the same way as the conventional mountain climbing method explained using FIG. 1, but after the motor 8 is reversed, (maximum 3 times) is different in that the electronic switch 31 is set to the B side and the mountain climbing loop is opened.

This operation will be explained with reference to FIG. The figure (a) shows the peak of the focal voltage, and the starting point of the helicoid operation is the new position of the helicoid.

This situation occurs, for example, when the helicoid at position h moves to position h2. Now, at the start of the mountain climbing operation, if the motor 8 starts moving the helicoid in the direction of climbing the mountain as shown in FIG. h
2, passes through position Mh2, reaches a position a little too far past the in-focus position h2 due to the inversion of the output signal of the terminal 61, moves in the opposite direction, passes the in-focus position h2 again, returns to the position, and then moves in the opposite direction. move in the direction. If the mountain-climbing loop is closed as is, the helicoid will continue to oscillate between position and position, as in the conventional case. However, it is known that the helicoid position has reached the vicinity of the focal point position h2 by detecting the two reversals. Therefore, in the configuration shown in FIG. 3, the counter 26 calculates the reversal signal which is the output signal of the terminal 61, and the information of the helicoid position h3 at the time of the first reversal is stored in the first helicoid position memory 27.
Then, information on the helicoid position h4 at the time of the second reversal is stored in the second helicoid position memory 28, and at the same time as the second reversal, the electronic switch 31 is set to the B side via the sum circuit 25 to complete the mountain climbing loop. Open.

Also, at the start of the mountain climbing operation, the motor 8 is activated as shown in Fig. 4 (C).
If you start moving the helicoid in the direction of going down the mountain as shown in (b), by the time you reach the in-focus position h2, the helicoid trajectory will have moved from position h1 to position 6 in the direction of h2 until it overlaps with the trajectory shown in Figure (b). The motor 8 needs to reverse once. In this case, the determination circuit 32, knowing that the output voltage of the terminal 61 has decreased at the start of the mountain climbing operation and is descending the mountain, resets the contents of the counter 26 after the first reversal, and performs the second reversal. ．． In order to prepare for the third reversal, in the case of Fig. 4(c), the second
3rd reversal, the helicoid position is in focus position h2
It is detected that the mountain has reached the vicinity of , and the mountain climbing loop is opened.

Now, at the same time that the content of the counter 26 becomes value 2 and the mountain climbing loop is opened, the content of the Birken point memory 16 is sequentially input to the comparison circuit I417, and the content of the first helicoid position memory 27. and a value obtained by averaging the contents of the second helicoid position memory 28 in an average value circuit 29,
The contents of the Birken Point memory 16 that are closest to this average value are stored in the Stop Birken Point memory 18.

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 converts the input contents of the stop Birken point memory 18 and A/D conversion. When the information on the helicoid position of the lens system 1, which is the output of the device 14, matches, the input line on the D side causes the motor drive circuit 30 to match.
and the second stage is completed. At this time, the information stored in the Birken point number memory 20 and the focal voltage memory 22 is erased by the output signal of the comparison circuit 19.

Next, the third stage, a case where refocusing becomes necessary due to a change in the distance between the subject and the camera or a change in the aperture value F and focal length f of the lens system 1, will be described.

When the aperture value F or focal length f of the lens system 1 changes, the contents of the Birken point number memory 20 input to the comparison circuit 21 and the new Birken point number input from the Birken point calculation circuit 15 are changed. If they are the same, there is no need to perform the focusing operation again. However, when these differ, the comparator circuit 21 performs the focusing operation again, so the sum circuit 21
4, 25 to connect the electronic switch 31 to the A side, and reset the counter 26 by the determination circuit 32.
Focusing operation starts from the first stage.

Furthermore, if the distance between the subject and the camera changes, the focal voltage that is the output of the A/D converter 13 input to the comparison circuit 23 and the output voltage of the focal voltage memory 22 will differ, so the difference between the two will be determined in advance. When the value exceeds the value, the comparator circuit 23 connects the electronic switch 31 to the A side via the summation circuits 24 and 25 in order to perform the focusing operation again, and the determination circuit 32 resets the counter 26, starting from the first stage. Start focusing operation.

In any of the above cases, after the motor 8 rotates, the initial value of the helicoid position is set to the position h as explained using FIG.
A new focal point can be reached through a process similar to that described with reference to FIG. 4, except that the value is different from the current value.

In addition, in the above explanation, we did not explain the case where the helicoid becomes close or at infinity ω during focusing operation, but in this case, the motor 8 is immediately reversed and then the operation is started. continue.

As explained above in detail using FIGS. 3 and 4, if the automatic focusing device according to the present invention is used, after focusing, changes in the aperture value of the lens, changes in focal length, movement of the subject, movement of the camera, etc. Since the helicoid can be completely stopped until it is necessary to perform a focusing operation again, good images can be taken without the vibration of the shooting angle caused by the vibration of the vericoid that existed in the conventional mountain climbing method.

It was explained that if the distance between the subject and the lens changes after focusing, the refocusing operation will start immediately if the focal voltage memory and the focal voltage at that point are different, but according to experiments, both It has been found that it is preferable to perform the refocusing operation only after a difference of about 10% to 20% has occurred.

In the detailed description of the present invention, the number of Birken points is set to be the minimum number to cover the depth of field without any gap, and the position of each Birken point is also selected to correspond to the number of Birken points. However, the number of Birken points used in the present invention may be any number as long as it is similar to the above minimum number, and in this case, the Birken point positions are such that the depth of field covered by each adjacent Birken point overlaps with each other. Needless to say, all you have to do is do it.

Furthermore, in a special case where the number of Birken Points calculated by the Birken Point calculation circuit 15 in FIG. 3 is 1, the helicoid may be unconditionally moved to that Birken Point without performing any mountain climbing motion.

[Brief explanation of the drawing]

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 shown in FIG. 1, and FIG. 3 is an example of an automatic focusing device according to the present invention. A block diagram showing the embodiment, FIG. 4 is a waveform diagram for explaining the operation of the configuration of FIG. 3. 1: Lens system, 2: Camera circuit (photoelectric conversion means)
, 7: motor drive circuit, 8: motor, 9: mountain climbing circuit (focal voltage detection means), 11 to 14: ] A/D converter,
15: Birken point calculation circuit, 16: Harken point memory, 17: comparison circuit. 18: Stop Birken point memory, 19: Comparison circuit,
20: Harken point number memory, 21: Comparison circuit, 2
2: Focal voltage memory (storage means), 23: Comparison circuit, 2
4, 25: Sum circuit, 26: Counter (focus state detection means), 27: First helicoid position memory, 28: Second helicoid position memory, 29: Average circuit, 30: Motor drive circuit, 31: Electronics switch (switch means). 32: Judgment circuit, 8: Motor Figure 1 Figure 2

Claims (1)

[Claims] 1. A photoelectric conversion means (2) for converting optical information into an electrical signal, a lens system (1) for forming an image of the optical information supplied from a subject onto the photoelectric conversion means, and the above-mentioned control signal generation means comprising a focus voltage detection means (9) for extracting high frequency components included in the electrical signal obtained by the photoelectric conversion means and generating a focus voltage corresponding to the focus degree of the lens system; A motor (8) that moves the position of the lens system in the optical axis direction, and a drive signal that controls the rotation of the motor by the focal voltage of the focal voltage detection means, and moves the lens system in the direction where the focal voltage is maximum. An automatic focusing device comprising: a motor drive circuit (7) for moving the lens system; a focusing state detection means (26) for detecting when the focal voltage has reached near the maximum value; When the in-focus state detection means reaches the focus state, it is opened by the output signal of the focus state detection means, cuts off the drive signal supplied from the control signal signal generation means to the motor drive circuit (7), and stops the rotation of the motor. switch means (31) for stopping the movement of the lens system; and storage circuits (20, 2) for storing electrical signals generated by the control signal generating means when rotation of the motor is stopped.
2) After the rotation of the motor is stopped, the electric signal generated by the control signal generating means and the electric signal stored in the storage circuit are compared, and the difference between the two is determined to be a predetermined value. comparator circuits (21, 2
3) An automatic focusing device for a video camera, etc., comprising: