JPH0636570B2 - Autofocus video camera - Google Patents

Description

TECHNICAL FIELD The present invention relates to an autofocus circuit for a video camera, which automatically adjusts the focus based on a video signal obtained from an image sensor.

(B) Conventional technology The method of using the image signal itself from the image sensor in the autofocus device of the video camera to evaluate the focus control state is essentially parallax-free and has a shallow depth of field. There are many advantages such as being able to focus accurately on a distant subject. Moreover, a special sensor for autofocus is not required, and the mechanism is extremely simple. Conventionally, an example of this autofocus method is "NHK".
A so-called hill-climbing servo control, which is described in "Technical Report" S40, Vol. 17, No. 1, Vol. 86, Vol. This hill-climbing servo control rotates the lens focus ring so that the amount of high-frequency components of the video signal is always maximized, so the lens does not remain stopped in the out-of-focus state, and it follows very well. It is a good method.

However, this method has a major drawback in that the lens is constantly moved.

One of the drawbacks is that the lens does not stop even if the subject is in focus, so that the shooting screen constantly shakes even after focusing on a stationary object. A lens currently used in a television camera changes a focal length by rotating a focus ring, which changes a field angle of a captured image. For this reason, in this method, in which the focus ring continues to vibrate even after focusing, the screen image becomes very difficult to see because the subject on the screen increases or decreases in a certain cycle.

The second drawback is power consumption. Currently, home video cameras often use a battery as a power source because of their portability, and when the focus motor is always driven to rotate forward and backward, the motor rotates in a certain direction due to inrush current. It consumes more power than necessary and shortens the recordable time. In addition, since the focus ring is always rotated, problems such as wear of gears occur.

Applicant filed in Japanese Patent Application No. 61-273212 (H04N 5/232)
We propose a new autofocus circuit method to eliminate these drawbacks. The outline of the contents 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) becomes a video signal by the image pickup circuit (4) including an image pickup element and is input to the focus evaluation value generation circuit (5). The focus evaluation value generation circuit (5) is constructed, for example, as shown in FIG. The vertical sync signal (VD) and the horizontal sync signal (HD) separated from the video signal by the sync separation circuit (5a) are input to the gate control circuit (5b) to set the sampling area. The gate control circuit (5b) sets a rectangular sampling area in the center of the screen based on the vertical sync signal (VD), horizontal sync signal (HD), and fixed oscillator output, and sets the brightness only within this sampling area. A gate opening / closing signal that allows the passage of a signal is supplied to the gate circuit (5c).

Only the luminance signal corresponding to the range of the sampling area is high pass filter (HPF) by the gate circuit (5c).
Only the high frequency component is separated after passing through (5d), and amplitude detection is performed by the detection circuit (5e) at the next stage. This detection output is the integration circuit (5
In f), it is integrated for each field and converted into a digital value in the A / D conversion circuit (5g) to obtain the focus evaluation value of the current field. The focus evaluation value generation circuit (5) configured as described above always outputs the focus evaluation value for one field.

Immediately after the start of the autofocus operation, the first focus evaluation value is held in the maximum value memory (6) and the initial value memory (7). After that, 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). Second
The 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.

The focus motor control circuit (10) rotates the focus motor (3) in the first direction until the second comparator (9) outputs a large or small output, and the current focus evaluation value is compared with the initial evaluation value. , If the output is larger than the preset fluctuation range, the rotation direction is kept as it is, and the current evaluation value is smaller than the fluctuation range as compared with the initial evaluation value. When the output is made, the rotation direction of the focus motor (3) is reversed and the output of the first comparator (8) is monitored.

The first comparator (8) compares the maximum focus evaluation value up to now held in the maximum value memory (6) with the current and evaluation values, and the current focus evaluation value is the contents of the maximum value memory (6). Bigger than
In the (first mode), the two comparison signals (S1) and (S2) of the above-mentioned preset first threshold value or less (second mode) are output. Here, the maximum value memory (6) is updated based on the output of the first comparator (8) when the current evaluation value is larger than the content of the maximum value memory (6), and the current value is always updated. The maximum evaluation value up to is held.

(13) is a motor position memory that stores a focus ring position by receiving a focus ring position signal indicating the position of the focus ring (2) supporting the lens (1),
Similar to the maximum value memory (6), the focus ring position when the maximum evaluation value is reached is updated based on the output of the first comparator (8).

The focus motor control circuit (10) monitors the output of the first comparator (8) while rotating the focus motor (3) in the direction determined based on the output of the second comparator (9), and In order to prevent malfunction due to noise, a second mode in which the current evaluation value is smaller than the preset first threshold value as compared with the maximum evaluation value is indicated by the output of the first comparator (8). At the same time, the focus motor (3) is reversed. After this reverse rotation, the contents of the motor position memory (13) and the current focus ring position signal are compared by the third comparator (14) and when they match, that is, the focus ring (2) has the maximum focus evaluation value. The focus motor control circuit (10) functions to stop the focus motor (3) when returning to the position. At the same time, the focus motor control circuit (10) outputs a range stop signal (LS).

(11) is the fourth memory that holds the focus evaluation value at that point when the lens stop signal (LS) is issued after the autofocus operation by the focus motor control circuit (10) is finished. This fourth memory (1
The content held in 1) is compared with the current focus evaluation value, and if the value becomes larger than the second threshold value for restart,
A subject change signal is output. When the focus motor control circuit (10) receives this signal, the focus motor control circuit (10) performs the autofocus operation again and follows the change of the subject.

The focus evaluation value generally has a mountain shape as shown in Fig. 5, but by changing the constant of the circuit that creates it, for example, by changing the cutoff frequency of the high-pass filter (H ・ P ・ F) for extracting high frequency components. It can be steep or gentle.
The shape of the peak of the focus evaluation value directly has a great influence on the autofocus operation. That is, 1) If the shape of the mountain is gentle, even if the focus is considerably out of focus, a certain degree of focus evaluation value can be obtained as shown in FIG. You can do and reach the focus. On the other hand, Fig. 6
As shown in (a), even if the subject distance changes while focusing on a certain subject, the subject moves at the same distance because the decrease in the focus evaluation value is small, or as shown in FIG. 7 (a). When the brightness changes, it cannot be distinguished from the change in the focus evaluation value, which causes a problem in continuous autofocus operation. That is,
In the former case, it is necessary to restart the autofocus operation, and in the latter case it is unnecessary.However, since the focus evaluation values are indistinguishable, if the former is prioritized, the latter case will occur. However, the screen is fluctuated because it is restarted without the need for restarting. If the latter is prioritized, the focusing operation will not be resumed and the screen will stop with blur even if a restart is required.

2) When the mountain shape is steep as shown in Fig. 5 (b), the focus evaluation value changes when the subject distance changes when the subject moves at the same distance [Fig. 6 ( The change in the evaluation value in [b)] is sufficiently larger than the change in [Fig. 7 (b)] when the brightness changes, so the above-mentioned malfunction does not occur.
At the hem of the mountain, the inclination is very small, so when it is out of focus, it is not possible to determine the direction in which the lens should move, and it continues to move in the opposite direction, or even if it moves in the correct direction, noise or slight movement of the subject causes , The instability of the motion occurs, that is, the direction of the skirt inclination changes, and the hem moves in the opposite direction.

An ordinary mountain-climbing servo-type autofocus camera uses an intermediate mountain shape so that these problems do not stand out. 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-mentioned two problems may become apparent depending on the situation, and malfunction may occur.

As a means for solving this problem, the Japanese Utility Model No. 61-72967 (H
04N 5/232), it has a first focus evaluation value generation circuit having a sharp focus evaluation value peak shape and a second focus evaluation value generation circuit having a gentle shape, and outputs these two outputs. A method has been proposed in which an accurate focusing operation is performed by constantly observing and comparing.

Generally, from the viewpoint of the accuracy of the focusing operation, it is desirable that the peak shape of the focus evaluation value is steep, but there is a problem that the shape of the peak tends to change due to the influence of noise and the like. Therefore, in the above invention, the focusing operation is performed with the gentle second evaluation value until the output of the first focus evaluation value generating circuit having a steep characteristic reaches a level that can be detected, and thereafter the first focus evaluation value generating circuit performs the focusing operation.
Focusing operation is performed with the evaluation value of. However, some subjects have almost no high-frequency components, and there are various mountain shapes depending on the shooting conditions such as shooting in a dark place, so which of the two focus evaluation value generation circuits is selected preferentially. There are many cases where it is impossible to uniquely determine whether or not to use the first focus evaluation value generation circuit, and the first focus evaluation value generation circuit causes a malfunction or the evaluation value output is small on the whole. In some cases, the output of the generation circuit is mainly composed of noise components rather than the video signal of the subject, which is a practical problem.

As means for solving such a practical problem, a first system including a first filter circuit having a high cutoff frequency and a corresponding first focus evaluation value generating circuit, and a low cutoff frequency are provided. By using a second filter circuit having a second focus evaluation value generating circuit and a second system including a second focus evaluation value generating circuit corresponding thereto, the first system until the value of the focus evaluation value exceeds a preset level. It is conceivable that the outputs of the first and second systems are alternately monitored, and when the set level is exceeded, the hill-climbing servo control is performed only by the first system.

This method automatically switches the focusing operation by the two focus evaluation value generating circuits, performs a fine focusing operation near the focusing point, and a rough focusing operation at a place far from the focusing point Has the advantage of improving the focusing speed.

However, this method also has one drawback. That is, when the in-focus state is reached, the focus evaluation value is generally detected by the first system, but when the focus evaluation value changes and a restart occurs, the first evaluation is performed. When the evaluation value is detected in the system, the focus ring moves slightly,
Since it reaches the skirt of the mountain shown in FIG. 5 (b) and the evaluation value becomes almost 0, the focusing operation becomes unstable and a malfunction occurs.

(C) Problems to be solved by the invention According to the conventional technology, after the focus is reached, a malfunction occurs when the camera is restarted or the camera is restarted after the focus is considerably out of focus. There were cases.

(D) Means for Solving the Problems The present invention is to perform the focusing operation by stopping the focus motor at the position where the focus evaluation value output as the high frequency component level of the video signal becomes the maximum value. The first focus evaluation value detection unit that shows a sharp change in the focus evaluation value with respect to the lens position and the second focus evaluation value detection unit that shows a gradual change with respect to the lens position are provided. After the focus motor stops at the position that is the evaluation value, the focus evaluation value is detected by the first focus evaluation value detection means until the focus evaluation value changes beyond the preset threshold for restarting. Immediately after the detection of the second focus evaluation value is changed, the second focus evaluation value is changed, and immediately after the restart, the second focus evaluation value detection means starts to detect the focus evaluation value, and then the second focus evaluation. Value detection means and first focus evaluation value detection By alternately using the means, when the output focus evaluation value exceeds a threshold value set in advance as a criterion for approaching the in-focus point,
It is characterized in that the detection method alternately performed is stopped and the detection is performed only by the first focus evaluation value detection means.

(E) Operation As a result of the configuration of the present invention as described above, when the in-focus state is reached and the focus motor is stopped, the in-focus state is determined by the first focus-evaluation-value detecting means. It can change rapidly and can follow small changes in the subject.
When the focus evaluation value has changed to a certain degree or more and a restart should be performed, the second focus evaluation value detecting means can quickly follow the change, and the focus evaluation value is to some extent. After the level is reached, the first focus evaluation value detection means can perform a fine focus search, so that the instability and malfunction at the time of restart as in the conventional example can be eliminated.

(F) Example An example of the present invention will be described below with reference to the drawings.
The same parts as those of the conventional example (FIGS. 2 and 3) are designated by the same reference numerals, and the description thereof will be omitted.

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

The image formed by the lens (1) becomes a luminance signal by the image pickup circuit (4) having an image pickup element and is input to the first and second filter circuits (15) and (16). Both filter circuits (15) and (16) are high-pass filters (HPF) that extract only the high-frequency components of the luminance signal, but the first filter circuit (15) is better than the second filter circuit (16). It has a high cutoff frequency. Specifically, the cutoff frequency of the first 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 controlled by the focus motor control circuit (10) by a switch circuit (selection means) (1
It is input to 7) and is alternately input to the integrating circuit (18). The integrating circuit (18) collectively shows the detecting circuit (5e), the integrating circuit (5f), and the A / D converting circuit (5g) shown in FIG. 3 of the conventional example. The filter circuits (15) and (16) are the HP of FIG.
It corresponds to F (5d). As a result, the first filter circuit
The first focus evaluation value generation circuit is composed of (15), the switch circuit (17), and the integration circuit (18), and the second focus circuit is composed of the second filter circuit (16), the switch circuit (17), and the integration circuit (18). The focus evaluation value generation circuit is constructed.

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

The output of the integrating circuit (18) is input to the switch circuit (19).
Similarly to the switch circuit (17), the switch circuit (19) outputs the output of the first focus evaluation value generation circuit to the first focus detection circuit (20) and the second focus evaluation value generation by the focus motor control circuit (10). The outputs of the circuits are 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 thereof are described in, for example, Japanese Patent Application No. 61-273.
Since it is described in No. 212, I will only outline it here.

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)
Rotate (3) in a predetermined direction to move the second comparator (20
d) Monitor the output. The second comparator (20d) compares the focus evaluation value after driving the focus motor with the initial evaluation value stored in the initial value memory (20b) and outputs the magnitude.

The focus motor control circuit (10) rotates the focus motor (3) in the first direction until the second comparator (20d) outputs a large or small output, and the current focus evaluation value is larger than the initial evaluation value. If the output says
If the current evaluation value is smaller than the initial evaluation value, the rotation direction of the focus motor (3) is reversed and the output of the first comparator (20c) is monitored.

The first comparator (20c) compares the current maximum focus evaluation value held in the maximum value memory (20a) with the current evaluation value, and the current focus evaluation value is stored in the maximum value memory (20a). The two comparison signals (S1) and (S2) that are larger (first mode) and sufficiently smaller (second mode) than (first mode) are output. Here, the maximum value memory (20a) is updated based on the output of the first comparator (20c) when the current evaluation value is larger than the content of the maximum value memory (20a) The maximum evaluation value of is retained.

(20e) is a motor position memory that stores the focus ring position by receiving a focus ring position signal that indicates the position of the focus ring (2) that supports the lens (1), and is the same as the maximum value memory (20a). Output of the first comparator (0c)
Based on (S1), the focus ring position when the maximum evaluation value is reached is updated so as to always be held.

The focus motor control circuit (10) monitors the output of the first comparator (20c) while rotating the focus motor (3) in the direction determined based on the output of the second comparator (20d), In order to prevent malfunction due to noise, the first comparator (20
c) The output instructs the second mode in which the current evaluation value is sufficiently smaller than the maximum evaluation value, and at the same time, the focus motor (3) is reversed. After this reverse rotation, the motor position memory (2
The content of 0e) and the current focus ring position signal are compared by the third comparator (20f), 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) functions to stop the focus motor (3). At the same time, the focus motor control circuit (10) outputs a lens stop signal (LS).

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

(11) is the fourth memory that holds the focus evaluation value at that point when the lens stop signal (LS) is issued after the autofocus operation by the focus motor control circuit (12) is finished. This fourth memory (1
The content held in 1) is compared with the current focus evaluation value, and when the difference becomes larger than the preset second threshold value,
Focus motor control circuit assuming that the subject has changed (10)
A subject change signal is output to and a restart is performed to follow the change of the subject.

On the other hand, the output from the second switch circuit (19) is the fifth comparator (1
4) is input and compared with the voltage of the reference voltage generation circuit (13), and when the output from the second switch circuit (19) <reference voltage, the L signal is output from the second switch circuit (19). When output> reference voltage, the H signal is input to the focus motor control circuit (10)
To enter.

When the focus motor control circuit (10) receives the signal of L, the focus operation is performed only by the output of the second focus detection circuit (21) while switching the switch circuits (17) and (19) for each field. Let me do it. Focus motor control circuit (10)
When the input to H is H, the switch circuits (17) and (1
In 9), only the output of the first focus evaluation value detection circuit is passed, and the focusing operation is performed only by the first focus detection circuit (20).

According to the method of the present invention having the above-mentioned configuration, the focusing operation is performed according to the evaluation value every other field when the output of the first focus evaluation value generating circuit <reference voltage. As described above, when the peak shape of the focus evaluation value is gentle, even if the evaluation value is detected intermittently, the value does not change so much, so that the mountain climbing servo can be performed with sufficiently high accuracy.

On the other hand, when the focus operation is performed with the focus evaluation value of a steep mountain, that is, when the output of the first focus evaluation value generation circuit> the reference voltage, the shape of the mountain near the maximum evaluation value is extremely steep. Therefore, it is desirable to perform a fine mountain climbing servo. In the present invention, as is apparent from the above description, in this case, only the output of the first focus evaluation value generation circuit is monitored, so the focusing operation is performed for all fields and the above conditions are satisfied. .

Detection of a subject change by the fourth comparator (12), that is, the current focus evaluation value and the content of the fourth memory (11) are compared, and when the difference between the two exceeds a second threshold value, focus motor control is performed. The circuit (10) issues a switch circuit control signal (SS),
A switch circuit so that only the signal from the second focus evaluation value generation circuit (16) is input to the focus motor control circuit (10).
The state of (17) and (19) is switched or held. That is, the focus motor control circuit (10) when the in-focus point is reached
When the input to the focus motor is through the first focus evaluation value generation circuit (15), the switch circuits (17) and (19) are switched, and the input to the focus motor control circuit (10) is the second focus evaluation value. If it is through the value generation circuit (16), the switch circuits (17) and (19) are controlled so as to be held in the current state.

As a result, when the focus evaluation value changes beyond the second threshold value, the focus operation is restarted by the output of the second focus evaluation value generation circuit (16), which has the characteristic that the curve of the focus evaluation value is gentle. To be done.

That is, when the focusing state is reached and the focusing operation by the first focusing detection circuit (20) or the second focusing detection circuit (21) ends, the switch circuits (17) and (19) switch to either contact. Even if the focus operation is restarted, the switch circuits (17) and (19) are unconditionally switched to the side where the focus operation is performed by the output of the second focus evaluation value generation circuit. It will be.

When the focusing operation is restarted, the focus motor control circuit (1
0) is the switching circuit (17), (19) for each field until the focus evaluation value exceeds the third threshold value corresponding to the reference voltage by the fifth comparator (14) whose focus evaluation value is preset. Focus detection is performed while switching, and if the third threshold value is exceeded, the focus operation is performed only by the first focus evaluation value generation circuit.

Advantages obtained by the present invention having the above-mentioned configuration will be described with reference to FIGS. 8 and 9.

8 and 9, the horizontal axis represents the lens focal length (distance between the lens and the subject) and the vertical axis represents the focus evaluation value, both of which show the states before and after the in-focus state and the restart. The curve (L) in the figure is the output and curve of the first focus evaluation value generation circuit.
(l) 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 the focusing operation using the output of the first or second focus evaluation value generation circuit. In the level, (H) is the second threshold value set as the level at which the restart should occur.

FIG. 8 shows the case where the output of the first focus evaluation value generation circuit exceeds the third threshold level, that is, the case where the output of the first focus evaluation value generation circuit performs focusing. Now, if the subject changes after reaching the in-focus point at the position of the subject distance A and comes to the position of B, for example, the curve (L)
And curve (l) changes to curve (M) and curve (m). At this time, since the lens position is at the point A, the output of the first focus evaluation value generating circuit, that is, the value of the curve (M) is 0 as shown in the figure. Therefore, if the focus motor control circuit (10) cannot specify the rotation direction of the motor when the focusing operation is performed by the output of the first focus evaluation value generation circuit,
The motor continues to rotate in the direction in which the motor has started to rotate first until an evaluation value exceeding the threshold value (G) is found. Therefore, when starting the rotation so that the initial direction of rotation at the time of restarting goes from point A to the left, there is no problem as far as the left, but when starting to rotate to the right, once the end point (infinite There may be a case where the state is defocused after going up to the point (distant point) and the image is out of focus until the point returns to point B, which is generally recognized as a malfunction.

However, as in the present invention, when the output of the second focus evaluation value generating circuit is switched to the curve (m) when the focus evaluation value becomes equal to or less than the second threshold value (H), the point (p) in the figure Since the evaluation value is detected at the position where the focus evaluation value has an inclination as shown in, the focus motor control circuit (10) can immediately determine the rotation direction of the focus motor, and the curve (m ), And when the value of the curve (M) exceeds the third threshold value (G), a fine focusing operation is started along the curve (M).

As another example, a case in which the subject changes slightly, for example, the subject distance moves to point C will be described.
In this case, the curves (L) and (l) are the curves (N) and
Come to (n). Since the lens position is at A, the evaluation value is (q ') for curve (N) and (q) for curve (n).
In this case, whichever of the curves (N) and (n) is used to detect the in-focus point, the inclination can be confirmed and the curve can be seen at first glance.
Although it is considered that (N) is used, it is possible to perform control with higher accuracy, but the output of the first focus evaluation value generation circuit is extremely susceptible to noise at such a low level, which causes a malfunction. Therefore, it is a very correct means to perform the focusing operation along the curve (n), and then to perform the focusing on the curve (N) when the third threshold value (G) is exceeded. When the C point is closer to the A point, that is, when the value at the (q ') point exceeds the level (G), whichever of the curves (N) and (n) is used for focus detection. The problem does not occur even if the above is performed, and rather the curve (N) should be used. However, when the output of the second focus evaluation value generation circuit is detected as described above, the first focus evaluation value generation circuit is performed for each field. Is detected and the output of the second focus evaluation value generation circuit is detected, the focusing operation is performed only by the output of the first focus evaluation value generation circuit after one field, and in such a case, the amount of movement of the lens. Is extremely small, no problem occurs even if the focusing operation is switched to the output of the second focus evaluation value generating circuit.

Next, as shown in FIG. 9, the first focusing operation is performed by 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 value (G). The case where the focus is reached will be described. Again, if the subject distance changes from A to B and the curves (L) and (l) change to (M) and (m), the value of (m) at the position A is the second threshold value ( The focus motor control circuit (10) outputs a subject change signal to rotate the motor (3) and the curve
The restart operation is performed according to (m). As described above, the values of the curves (M) and (m) are alternately observed for each field during the restart operation, and when the value of the curve (M) exceeds the threshold value (G), the focusing operation is performed by the curve. It will be done by (M).

Consider again the case where the subject distance is changed to C as in the case of FIG. In this case, obviously the second threshold (H) of restart
Since there is no change beyond, no reboot is done. If the first focusing operation is performed by the output of the second focus evaluation value generation circuit from this fact, after the subject distance has changed considerably,
That is, it can be seen that the restart is not performed unless the focus is considerably out of focus. This seems to be a major problem, but the focusing operation is actually executed by the second focus evaluation value generation circuit, for example, in the case of a subject such as a white wall where the screen fluctuation is extremely small. Even if it is out of focus, it does not affect the shooting screen.

As is apparent from the above description, it is important to be able to quickly deal with the case where the first focusing operation is performed by the first focus evaluation value generation circuit. Rebooting is required in the actual shooting state when the subject distance changes significantly or when the subject itself changes to another object.In such a case, the focus evaluation value generally changes greatly. Immediately after the restart is started as described above, it is extremely important and appropriate to perform the focusing operation by the second focus evaluation value generating circuit.

(G) Effect of the Invention As described above, in the present invention, when the focus operation is performed by the two focus evaluation value generation circuits and then the restart is performed,
Since the focusing operation immediately after restarting is performed using the second focus evaluation value generation circuit having a gentle mountain shape of the focus evaluation value, it is possible to perform high-speed tracking without losing the subject. Become.

[Brief description of drawings]

FIG. 1, FIG. 4, FIG. 8 and FIG. 9 relate to an embodiment of the present invention. FIG. 1 is a circuit block diagram, FIG. 4 is a main circuit block diagram, FIG. 8 and FIG. [Fig. 6] is an operation explanatory view of the present invention. 2 and 3 are circuit block diagrams of a conventional example. In addition, FIGS. 5, 6, and 7 depend on shooting conditions.
It is explanatory drawing of the fluctuation | variation of the output of one focus evaluation value generation circuit. (1) …… Lens, (3) …… Focus motor, (9) ……
Focus motor control circuit, (15) ...... first filter,
(16) …… second filter, (17) …… switch circuit (selection means), (18) …… integration circuit, (19) …… switch circuit, (2
0) ... first focus detection circuit, (21) ... second focus detection circuit,
(12) …… 4th comparison circuit, (13) …… Reference voltage generation circuit, (S
S) …… Switch circuit switching signal.

Claims (1)

[Claims] 1. A first focus evaluation value detection means for outputting a high frequency component level of a luminance signal obtained from an image sensor as a first focus evaluation value, and a component of a lower frequency region than the high frequency component level of the luminance signal. And a second focus evaluation value detection means for outputting a level including the following as a second focus evaluation value, and whether or not the first focus evaluation value has reached a predetermined value.
A selection unit that outputs one of the both focus evaluation values as a true focus evaluation value, and the true focus evaluation value is the maximum evaluation value by displacing a focus lens according to the focus evaluation value output from the selection unit. The focus operation is stopped at the following focus position, and the focus operation is restarted when the true evaluation value changes to a preset reference value or more after the focus operation ends. An autofocus video camera comprising: focus control means; and means for controlling the selection means so that the second focus evaluation value is output as a true focus evaluation value when the focusing operation is restarted.