JPS63215268A - Automatic focus video camera - Google Patents

Abstract

PURPOSE:To attain high-speed tracking by using two focus evaluation generating circuits to apply focusing and using a 2nd focus evaluation value generating circuit in which the shape of focus evaluation is a slow mountainous form in applying the focusing just after restart. CONSTITUTION:Since the cutoff frequency of a 1st focus value generating circuit is higher than that of the 2nd focus evaluation value generating circuit, the focus evaluation being its output is steeper than that of the focus evaluation value from the 2nd focus value generating circuit. When the focusing by a 1st focus detection circuit 20 or the 2nd focus detection circuit 21 is finished, even when switch circuits 17, 19 are switched to any contact, the switch circuits 17, 19 are switched to the position to apply focusing by the output of the 2nd focus evaluation value generating circuit unconditionally when the focusing is restarted. Thus, the instability at restarting or malfunction is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to an autofocus circuit for a video camera that automatically adjusts focus based on a video signal obtained from an image sensor.

(b) Conventional technology The method of using the video signal itself from the image sensor to evaluate the focus control state in the autofocus device of a video camera is essentially free of parallax and is difficult to use when the depth of field is shallow or Conventionally, this autofocus method has many advantages such as being able to focus accurately even on distant subjects, and is mechanically extremely simple and does not require a special sensor for autofocus. An example is “
NHK Technical Report” S40, @Volume 17, No. 1, Tomaki 86
So-called mountain-climbing servo control is known, as described in Ishida et al.'s "Automatic focus adjustment of television cameras using mountain-climbing servo system" on page 21 of the issue.This mountain-climbing servo control always focuses on the high range of the video signal Since the lens rotates, the lens does not remain stationary when it is out of focus, making it an extremely easy-to-follow method.

However, this method has a major drawback due to the constant movement and control of the lens.

One of the drawbacks of this is that the lens does not stop even after focusing, so the shooting screen continues to shake even after focusing on a stationary object. The lens currently used in television cameras changes the focal length by rotating the focus ring, which changes the angle of view of the photographed image. For this reason, with this method, where the focus ring continues to vibrate even after focusing, the subject on the screen becomes sharp or small at certain intervals, making the screen extremely difficult to see.

The second drawback is power consumption. Currently, home video cameras are often powered by batteries for their portability, and when the focus motor is constantly driven (forward and reverse), the motor is turned in a fixed direction for the rush 1E flow. It consumes more power than when rotating, and the available shooting time becomes shorter.

In addition, constant rotation of the focus ring causes other problems such as gear wear.

The applicant filed Japanese Patent Application No. 61-273212 (HO4N S/
232), proposes a new autofocus circuit system to eliminate these drawbacks. The outline of the content will be described below as a conventional example.

FIG. 2 is a block diagram of the autofocus circuit according to the above application.

The image formed by the lens (1) is converted into image No. 13 by an image pickup circuit (4) including an image pickup element, and is input to a focus evaluation value generation circuit (5). Focus evaluation value generation circuit (5
) is configured, for example, as shown in FIG. A vertical synchronization signal (VD) and a horizontal synchronization signal (HD) separated from the video signal by a synchronization separation circuit (5a) are input to a gate control circuit (5b) to set a sampling area. In the gate control circuit (5b), the vertical synchronization signal (V
D) Based on the horizontal synchronization signal (HD) and a fixed oscillator output, a rectangular sampling area is set in the center of the screen, and a gate opening/closing signal is sent to the gate circuit to allow the luminance signal to pass only within this sampling area. (5C)
supply to.

Only the luminance signal corresponding to the range of the sampling area is filtered by the gate circuit (5c) through the high-pass filter (H
, P, F) (5d), only the high frequency components are separated, and the amplitude is detected in the next stage detection circuit (5e).

This detection output is integrated for each field by an integrator circuit (5f) and converted into a digital value by an A/D converter circuit (5g) to obtain a focus evaluation value for the current field. The focus evaluation value generation circuit (5) always outputs the focus evaluation value for one field.

Immediately after starting the autofocus operation, the initial focus evaluation value is stored in the maximum value memory (6) and the initial value memory (7). Thereafter, the focus motor control circuit (focus motor control means) (10) rotates the focus motor (3) in a predetermined direction and monitors the output of the second comparator (9). The second comparator (9) compares the focus evaluation value after driving the focus motor with the initial value evaluation value held in the initial value memory (7) and outputs the magnitude thereof.

The focus motor control circuit (10) includes a second comparator (9).
) rotates the focus motor (3) in the initial direction until it outputs an output that is large or small, and outputs that the current focus evaluation value is larger than the initial evaluation value by a preset variation range. If the current evaluation value is smaller than the initial evaluation value and the above fluctuation range is output, the focus rotation direction (3) is Reverse the direction of rotation and look at the output of the first comparator (8).

The first comparator (8) compares the maximum focus evaluation value that has been stored in the maximum value memory (6) with the current evaluation value,
Two types of comparison signals (51
)(52) is output. Here, the maximum value memory (6) is
Based on the output of the first comparator (8), if the current evaluation value is larger than the contents of the maximum value memory (6), that value is updated, and the maximum evaluation value up to now is always held. Ru.

(13) is a focus ring (13) that supports the lens (1).
2) is a motor position memory that stores the focus ring position upon receiving the focus ring position signal that indicates the position of the first comparator (8), similar to the maximum value memory (6).
Based on the output of , the focus ring position is updated so as to always maintain the focus ring position when the maximum evaluation value is reached.

The focus motor control circuit (10) includes a second comparator (9).
) focus motor (3) in the direction determined based on the output.
) while looking at the output of the first comparator (8),
In order to prevent malfunctions due to noise in the evaluation value, a second mode is set in which the current evaluation value at the output of the first comparator (8) is smaller than the preset first threshold value compared to the maximum evaluation value. At the same time as instructed, the focus motor (3) is reversed. After this reversal, the contents of the motor position memory (13) and the current focus ring position signal are transferred to the third comparator (
14) and when they match, that is, when the focus ring (2) returns to the position where the focus evaluation value is maximum, the focus motor control circuit (10) stops the focus motor (3). do. At the same time, the focus motor control circuit (10) outputs a lens stop signal (LS).

(11) indicates when the autofocus operation by the focus motor control circuit (10) is completed and the lens stop signal (LS
) is issued, and at the same time the focus evaluation value at that time is held.The fourth comparator (12) in the subsequent stage compares the contents held in this fourth memory (11) with the current focus evaluation value. When the comparison is made and the value becomes larger than the second threshold for restarting, a subject change signal is output. When the focus motor control circuit (10) receives this signal, it restarts the autofocus operation to follow changes in the subject.

The focus evaluation value generally has a mountain shape as shown in Figure 5, but it can be changed by changing the constants of the circuit that creates it, such as the cutoff frequency of the bypass filter (H・P-F) for extracting high frequency components. It can be steep or gradual. The shape of this peak of focus evaluation values has a direct and significant effect on autofocus operation. In other words, 1) If the shape of the mountain is gentle, a focus evaluation value of a certain size can be obtained as shown in Figure 5 (a) even if the focus is quite blurred, so it is possible to use reliable mountain climbing servo. You can do this and achieve focus. On the other hand, as shown in Figure 6(a), even if the subject distance changes when the subject is in focus, the focus evaluation value does not decrease much, so the subject may move at the same distance or As shown in (a), when the brightness changes, it cannot be distinguished from the change in the focus evaluation value, causing a problem in continuous autofocus operation. In other words, in the former case, it is necessary to restart the autofocus operation, and in the latter case, it is unnecessary, but since the focus evaluation value is indistinguishable, if the former is prioritized, the latter situation will occur. In some cases, a restart is performed even though there is no need to restart, resulting in screen blurring.

If the latter is given priority, even if a restart is required, the focusing operation will not restart and the screen will remain blurry.

2) When the shape of the mountain is steep as shown in Figure 5 (b), the change in the focus evaluation value when the subject distance changes is the same as when the subject moves at the same distance [Figure 6 ( The change in the evaluation value of [see Fig. 7 (b)] is sufficiently large compared to the change when the brightness changes [Fig. 7 (b)], so the above-mentioned malfunction does not occur. When the lens is out of focus because it is small, it is not possible to determine the direction in which the lens should move, and it may continue to move in the opposite direction, or even if it is moving in the correct direction, noise or slight movement of the subject may cause the lens to change the direction of the slope of the hem. This causes instability in the movement, where the object starts to move in the opposite direction.

Autofocus cameras using the normal mountain climbing servo system use intermediate mountain shapes to make these problems less noticeable. However, since the shape of the mountain changes depending on the subject, its brightness, and the focal length of the lens, one of the above two problems may become apparent depending on the situation, and a malfunction may occur.

As a means to solve this problem,
No. 7 (HO4N 5/232), the focus evaluation value has a first focus evaluation value generation circuit with a steep shape and a second focus evaluation value generation circuit with a gentle shape. However, a method has been proposed in which accurate focusing is performed by constantly observing and comparing these two outputs.

Generally, from the viewpoint of accuracy of focusing operation, it is desirable that the shape of the peak of the focus evaluation value be steep, but there is a problem that the shape of the peak is easily changed due to the influence of noise and the like. Therefore, in the above invention, focusing is performed using a gentle second evaluation value until the output of the first focus evaluation value generation circuit, which has a steep characteristic, reaches a detectable level, and thereafter, the focus operation is performed using the second evaluation value. Focusing is performed based on the evaluation value. However, depending on the subject, there are some that have almost no high-frequency components, and there are various shapes of mountains depending on the shooting conditions, such as when shooting in a dark place, so which of the two focus evaluation value generation circuits is selected preferentially. There are many cases in which it is not possible to uniquely determine whether the focus evaluation value should be The output of the generating circuit is the image of the subject 18
In some cases, it is mainly composed of noise components, which poses a practical problem.

As a means to solve such practical problems, there is a first system consisting of a first filter circuit with a high cutoff frequency and a corresponding first focus evaluation value generation circuit, and a first system with a low cutoff frequency. and a second focus evaluation value generating circuit corresponding to the second filter circuit.
system, the outputs of the first system and the second system are alternately monitored until the value of the focus evaluation value exceeds a preset level, and when the value exceeds the preset level, the One possible method is to perform mountain climbing servo control using only one system.

This method automatically switches the focusing operation by two focus evaluation value generation circuits, performs fine focusing near the in-focus point, and performs rough focusing at a considerable distance from the in-focus point. This has the advantage of improving focusing speed.

However, this method also has one drawback. In other words, when focus is reached, the first system generally performs one focus evaluation, but if the focus evaluation value changes and restarts, the first system When detecting the evaluation value using this system, if the focus ring moves only slightly, it will reach the foot of the mountain shown in Figure 5(b), and the evaluation value will be almost 0.
As a result, the focusing operation becomes unstable, leading to malfunctions.

(c) Problems to be solved by the invention According to the prior art, a malfunction occurs when restarting the camera after it has achieved focus, or the restart is performed after the focus is considerably out of focus. There was a case.

(2) Means for Solving Problems The present invention performs a focusing operation by stopping the focus morph at the position where the focus evaluation value output as the high-frequency component level of the video signal becomes the maximum value. In this case, the focus evaluation value has a first focus evaluation value detection means in which the focus evaluation value shows a steep change with respect to the lens position, and a second focus evaluation value detection means in which the focus evaluation value shows a gradual change in relation to the lens position. After the focus morph stops at the position where the evaluation value is obtained, the focus evaluation value is determined by the first focus evaluation value detection means until the focus evaluation value changes beyond the preset threshold for restarting. Immediately after the second focus evaluation value detecting means detects the focus value, changes beyond the second threshold value, and restarts, the focus evaluation value 1iI is detected by the second focus evaluation value detection means.
After starting to detect the li value, the second focus evaluation value detection means and the first focus evaluation value detection means are used alternately until the output focus evaluation value is close to the in-focus point. If a threshold value preset as a determination criterion is exceeded, the alternate detection method is stopped and detection is performed only by the first focus evaluation value detection means.

(E) Effect As a result of the present invention configured as described above, when the focus morph has reached the in-focus point and the focus morph has stopped, the focus state is determined by the first focus evaluation value detection means, so that the focus evaluation value is It changes rapidly and can follow even the slightest changes in the subject.

When the focus evaluation value changes more than a certain degree and a restart is required, the second focus evaluation value detection means can quickly follow the change, and when the focus evaluation value changes to a certain degree. After reaching the level, the first focus evaluation value detecting means can perform a detailed in-focus point search, thereby eliminating the instability and malfunctions that occur in the prior art upon restart.

(f) Example Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

Incidentally, the same parts as in the conventional example (FIGS. 2 and 3) are given the same reference numerals, and explanations thereof will be omitted.

FIG. 1 is a circuit block diagram of an automatic focusing system according to this embodiment.

The image formed by the lens (1) is turned into a luminance signal by an imaging circuit (4) having an imaging element, and is input to the first and second filter circuits (15) and (16). Both filter circuits (15) and (16) are bypass filters (1) that extract only the high frequency components of the luminance signal.
．． P, F), but the first filter circuit (15) has a higher cutoff frequency than the second filter circuit (16). Specifically, the first filter circuit (
The cutoff frequency of the filter circuit (15) is set to 500 kHz, and that of the second filter circuit (16) is set to 100 kHz. The outputs of the filter circuits (15) and (16) are input to the switch circuit (selector 1 stage) (17) controlled by the focus motor control circuit (10), and are alternately input to the integration circuit (18). . The integration circuit (18) is a detection circuit (5e) and an integration circuit (5e) shown in FIG. 3 of the conventional example.
f), A/D conversion circuit (5g) is collectively shown. Further, the filter circuits (15) and (16) correspond to HP F (5d) in FIG. As a result, the first
The filter circuit (15), the switch circuit (17>, and the integration circuit (18) constitute a first focus evaluation value generation circuit,
2nd filter circuit <16), switch circuit <17),
The integration circuit (18) constitutes a second focus evaluation value generation circuit.

The first focus evaluation value generation circuit has a cutoff frequency that is
Since the focus evaluation value is higher than that of the second focus evaluation value generation circuit, the focus evaluation value output from the second focus evaluation value generation circuit has a steeper peak shape than the focus evaluation value from the second focus evaluation value generation circuit.

The output of the integration circuit (18) is input to the switch circuit <19). The switch circuit (19) is the switch circuit (17)
Similarly, by the focus motor control circuit (10),
The output of the first focus evaluation value generation circuit is the output of the first focus detection circuit (2
0), the outputs of the second focus evaluation value generation circuit are respectively input to the second focus detection circuit (21).

The focus detection circuits (20) and (21) specifically have the configuration shown in FIG. 4, and the details are described in, for example, Japanese Patent Application No. 61-273212. I'll just give a summary.

The first focus evaluation value obtained immediately after the start of the focusing operation is held in the maximum value memory (20a) and the initial value memory (20b). After that, the focus motor control circuit (10) rotates the focus morph (3) in a predetermined direction,
Take a look at the output of the second comparator (20d). Second comparator (2
0d) compares the focus evaluation value after driving the focus motor with the initial evaluation value held in the initial value memory (20b), and outputs the magnitude thereof.

The focus motor control circuit (10) includes a second comparator (20
d) rotates the focus morph (3) in the initial direction until it outputs a large or small output, and if it outputs that the current focus evaluation value is larger than the initial evaluation value, it remains as it is. The rotation direction is maintained, and if the current evaluation value is smaller than the initial evaluation value, focus morph (
3) reverse the rotation direction and monitor the output of the first comparator (20c).

The first comparator (20c) compares the current maximum focus evaluation value stored in the maximum value memory (20a) with the current evaluation value, and determines that the current focus evaluation value is the content of the maximum value memory (20a). Two types of comparison signals (5
1) Output (52). Here, maximum value memory (20a
) is updated based on the output of the first comparator (20c) if the current evaluation value is larger than the content of the maximum value memory (20g), and the maximum value of the evaluation values up to now is always updated. Retained.

(20e) is a motor position memory that receives a focus ring position signal indicating the position of the focus ring (2) that supports the lens (1) and stores the focus ring position, and is similar to the maximum value memory (20a). Based on the output (Sl) of the first comparator (20c), the focus ring position can be updated so as to always maintain the focus ring position when the maximum evaluation value is reached.

The focus motor control circuit (10) includes a second comparator (2
0d) While rotating the focus motor (3) in the direction determined based on the output, closely monitor the output of the first comparator (20c) and prevent malfunctions due to noise in the evaluation value.
The focus motor (3) is reversely rotated at the same time as the second mode in which the current evaluation value is sufficiently smaller than the maximum evaluation value is instructed by the output of the first comparator (20c). After this reversal, the contents of the motor position memory (20e) and the current focus ring position signal are compared by the third comparator (20f), and when they match, that is, the focus ring (2) has the maximum focus evaluation value. The focus motor control circuit (10) functions so that the focus motor (3) can be stopped and moved when the lens returns to the position where .At the same time, the focus motor control circuit (10) outputs a lens stop signal (LS). .

The focus detection circuit (21) also has exactly the same configuration as the focus detection circuit (20).

(11) indicates that the autofocus operation by the focus motor control circuit (12) has been completed and the lens stop signal (L
S) is issued, and at the same time the focus evaluation value at that time is held, and the fourth comparator (12) in the subsequent stage
The content held in this fourth memory <11) is compared with the current focus evaluation value, and if the difference becomes larger than a preset second threshold, it is assumed that the subject has changed and the focus motor control is performed once. At (10), a subject change signal is output, and restart is performed to follow the change in subject.

On the other hand, the output from the second switch circuit (19) is input to the fifth comparator (14), and is compared with the voltage of the reference voltage generation circuit (13). In the case of voltage, the L signal is sent to the second switch circuit (1
Output from 9) In the case of reference voltage, an H signal is input to the focus motor control circuit (10).

When the focus motor control circuit (10) receives the L signal, it switches the switch circuits (17) and (19) for each field and performs the focusing operation only by the output of the second focus detection circuit (21). Let them do it.

When the input to the focus motor control circuit (10) is H, the switch circuits (17) and (19) pass only the output of the first focus evaluation value detection circuit, and the input to the first focus detection circuit (20 ), the focusing operation is performed only by

As a result of the above-described configuration, according to the method of the present invention, in the case of the reference voltage output from the first focus evaluation value generation circuit, the focusing operation is performed based on the evaluation value of every other field. As described above, when the shape of the peak of the focus evaluation value is gentle, even if the evaluation value is detected intermittently, the value does not change much, so that hill climbing servo can be performed with sufficiently high accuracy.

On the other hand, when focusing is performed using a focus evaluation value with a steep peak, that is, when the output of the first focus evaluation value generation circuit is > the reference voltage, the shape of the peak near the maximum evaluation value is extremely steep. Therefore, it is desirable to perform fine-grained mountain climbing servo.As is clear from the above explanation, in this case, only the output of the first focus evaluation value generation circuit is monitored in the present invention. has been carried out and the above conditions are satisfied.

When the fourth comparator (12) detects a change in the subject, that is, the current focus evaluation value is compared with the contents of the fourth memory (11), and the difference between the two exceeds the second threshold, the focus motor is controlled. The circuit (10) receives a switch circuit control signal (
55) to switch the states of the switch circuits (17) and (19) so that only the signal from the second focus evaluation value generation circuit (16) can be input to the focus motor control circuit (10), or Hold. That is, the input to the focus motor control circuit (10) when the in-focus point is reached is the first
If the input is via the focus evaluation value generation circuit (15), the switch circuits (17) and (19) are switched so that the input to the focus morph control circuit M(10) is transmitted through the second focus evaluation value generation circuit (16). ), the switch circuits (17) and (19) are controlled to remain in their current state.

As a result, when the focus evaluation value changes beyond the second R(if), the output of the second focus evaluation value generating circuit (16), which has a characteristic that the curve of the focus evaluation value is always gentle,
Focusing operation is resumed.

That is, when the in-focus state is reached and the focusing operation by the first focus detection circuit (20) or the second focus detection circuit 21) is completed, the switch circuit (17) (19) is connected to which contact point. Even if the focusing operation is switched, when the focusing operation is restarted, the switch circuits (17) and (19) are unconditionally switched to the side where the focusing operation can be completed with the output of the second focus evaluation value generation circuit. It turns out.

When the focusing operation is resumed, the focus morph control circuit (
10) is a fifth comparator (14) in which a focus evaluation value is preset.
), focus detection is performed while switching the switch circuits (17) and (19) for each field until the focus evaluation value exceeds the third threshold corresponding to the reference voltage. Focusing operation is performed only by the focus evaluation value generation circuit.

The advantages obtained by adopting the above-described configuration of the present invention will be explained with reference to FIGS. 8 and 9.

In FIGS. 8 and 9, the horizontal axis is the lens focal length (distance between the lens and the subject), and the vertical axis is the focus evaluation value, both of which show the states before and after reaching focus and restarting. The curve (L) in the figure is the output of the first focus evaluation value generation circuit, the curve (ffi) is the output of the second focus evaluation value generation circuit, and (G)
is the third threshold value set as a reference value for performing a focusing operation using the output of the first or second focus evaluation value generation circuit, and (H) is set as a level for causing a restart. This is the second threshold value.

FIG. 8 shows a case where the output of the first focus evaluation value generation circuit exceeds the third threshold level, that is, a case where focusing is performed using the output of the first focus evaluation value generation circuit. Now, suppose that after reaching the in-focus point at a position of subject pressure 1111A, the subject changes and comes to, for example, position B. The curve (L) and the curve (!) are respectively the curves () shown by broken lines.
M) and curve (m). At this time, since the lens position is at point A, the output of the first focus evaluation value generation circuit, that is, the value of the curve (M), is 0 as shown. Therefore, when trying to perform a focusing operation using the output of the first focus evaluation value generation circuit, the focus morph control circuit (10) cannot specify the rotation direction of the motor, and the evaluation value exceeding the first threshold (G) The motor will continue to rotate in the direction in which it first started rotating until the value is found. Therefore, if the initial direction of rotation at restart is from point A to the left, there will be no problem as shown in the left, but if the rotation starts to the right, once the end point (in this example, infinite After reaching the far point (far point), there may be a case where the image is reversed and remains out of focus until it returns to point B, which can generally be recognized as a malfunction.

However, as in the present invention, when the focus evaluation value becomes equal to or less than the second threshold value (H), if the output of the second focus evaluation value generation circuit, that is, the curve (m) is switched, then the point (p) in the figure As shown in , since the evaluation value is detected at the position where the slope of the focus evaluation value exists, the focus morph control circuit (10) can immediately determine the rotation direction of the focus morph, and the curve (m ), and when the value of the curve (M> exceeds the third threshold (G)), a fine focusing operation begins along the curve (M).

As another example, we will discuss a case where the subject changes slightly, for example, a case where the subject distance moves to 0 point.

In this case, curves (L) and (ffi) come to curves (N) and (n), respectively. Since the lens position is at A,
The value of the evaluation value is (q゛) for the curve (N), and the value of the evaluation value is (q゛) for the curve (N).
) becomes (q>. In this case, the curve (N) and (
No matter which method is used to detect the focused point, it is possible to check the inclination, and it is considered that using the - viewing curve (N) allows for more accurate control, but the first focus evaluation value generation circuit The output is extremely susceptible to noise at such low levels, causing malfunctions. For this reason, the curve (
After performing the focusing operation along the third threshold (G
) is an extremely correct method to focus using the curve (N). When the 0 point is closer to the A point, that is, when the value of the (q') point exceeds the level (G), which of the curves (N) and (n) is used to detect the focused point? However, as mentioned above, when detecting the output of the second focus evaluation value generation circuit, the first focus evaluation value generation circuit should be used for each field. Since the output of the focus evaluation value generation circuit and the output of the second focus evaluation value generation circuit are detected, the focusing operation is performed only by the output of the first focus evaluation value generation circuit after one field. Since this is extremely small, no problem will occur even if the focusing operation is once switched to the output of the second focus evaluation value generation circuit.

Next, as shown in Fig. 9, the first focusing operation is performed using the output of the second focus evaluation value generation circuit, that is, the output of the first focus evaluation value generation circuit does not exceed the third threshold (G). Let's discuss the case when focus is reached. Again, if the subject distance changes from A to B, and the curve (L>, (p) changes to (M) and (m>), then the value of (m) at position A is the second threshold for restart ( The focus morph control circuit (10) outputs an object change signal and controls the motor (3).
), and the restart operation is performed along the curve (m). As mentioned above, during the restart operation, the values of curve (M) and (m) can be observed alternately for each field, and the curve (
When the value of M) exceeds the threshold (G), the focusing operation follows the curve (
This will be done by M>.

Consider again the case where the subject distance changes to C as in the case of FIG. In this case it is clear that the second restart threshold (H
), so restarting is not performed.If the initial focusing operation is performed using the output of the second focus evaluation value generation circuit, after the subject distance has changed considerably, i.e. You can see that the restart will not occur unless the focus is very blurred. This may seem like a big problem at first glance, but the focusing operation is actually performed by the second focus evaluation value generation circuit when the subject has very little fluctuation in the screen, such as a white wall. Even if the focus is slightly blurred, it will not have a major effect on the shooting screen.

As is clear from the above description, it is important to be able to respond quickly when the first focusing operation is performed by the first focus evaluation value generation circuit.

In actual shooting conditions, restarting is required when the subject distance changes significantly or when the subject itself changes to something else. In such cases, the focus evaluation value generally fluctuates greatly, so as mentioned above, Immediately after starting the restart, as explained in the above, it is extremely important and appropriate to perform the focusing operation using the second focus evaluation value generation circuit.

(G) Effects of the Invention As described above, in the present invention, when restarting after focusing operation using two focus evaluation value generation circuits,
The focusing operation immediately after restarting is performed using the second focus evaluation value generation circuit whose focus evaluation value is in the shape of a gentle mountain, making it possible to perform high-speed tracking without losing sight of the subject. Become.

[Brief explanation of the drawing]

1, 4, 8 and 9 relate to an embodiment of the present invention, in which FIG. 1 is a circuit block diagram, FIG. 4 is a main circuit block diagram, and FIGS. 8 and 9. FIG. 2 is an explanatory diagram of the operation of the present invention. FIGS. 2 and 3 are circuit diagrams of a conventional example. Further, FIGS. 5, 6, and 7 are explanatory diagrams of fluctuations in the outputs of the two focus evaluation value generation circuits depending on photographing conditions. (1)...lens, (3)...focus morph,
(9)... Focus morph control circuit, (15)...
・First filter, (16)...second filter,
(17)...Switch circuit (selection means), (18)...
...Integrator circuit, (19)...Switch circuit, (20)
...First focus detection circuit, (21)...Second focus detection circuit, (12>...Fourth comparison circuit, (13)...Reference voltage generation circuit, (55)...・Switch circuit switching signal.

Claims (1)

[Claims] (1) a first focus evaluation value detection means for outputting a high frequency component level of a video signal obtained from an image sensor as a first focus evaluation value; a second focus evaluation value detection means for outputting a level including the second focus evaluation value as a second focus evaluation value; and depending on whether the first focus evaluation value reaches a predetermined value,
a selection means for outputting one of the two focus evaluation values as a true focus evaluation value; and a selection means for stopping a focus motor at a position where the true focus evaluation value becomes a maximum evaluation value; focus motor control means for restarting the focus motor when the true focus evaluation value changes to a preset reference value or more; An autofocus video camera characterized in that a second focus evaluation value is selected as a true focus evaluation value.