JPH0644807B2 - Autofocus video camera - Google Patents

Description

The present invention relates to an image pickup apparatus having an autofocus mechanism for automatically adjusting a focus based on a video signal obtained from an image pickup device and a zoom mechanism.

(B) Conventional technology In an autofocus device for video cameras, the method of using the image signal from the image sensor itself to evaluate the focus control state is essentially a method in which there is no parallelism and the depth of field is shallow. There are many advantages such as being able to accurately focus on a distant subject. Moreover, a special sensor for the autofocus is unnecessary, and the mechanism is extremely simple.

This type of autofocus circuit basically controls the focus motor by a control method called a hill-climbing servo system as disclosed in JP-A-60-103776 (H04N5 / 232). That is, one field of the high frequency component of the luminance signal in the picked-up image signal is detected as the focus evaluation value, and this focus evaluation value is constantly compared with the one before the field, so that the focus motor always has a maximum value. It keeps microvibrating.

Also, as seen in Japanese Utility Model Publication No. 60-135712 (G02B7 / 11), the point where the evaluation value changes from an increasing tendency to a decreasing tendency by driving the focus ring in one direction is set as the maximum point, and the focus is set at this point. Some return the ring and stop it.

In detecting this maximum point, the focus evaluation value is compared for each field, the larger one is always stored as the maximum value, and when it is detected that a predetermined level (threshold value) is dropped from this maximum value, This is done by determining the maximum value as the maximum point, and usually this threshold value is a preset fixed value.

Also, if the subject moves and becomes out of focus after the focus motor is brought into focus and the focus motor is stopped, it becomes necessary to restart the focus operation, and the motor is restarted using the focus evaluation value. It is common to make timing decisions. That is, the focus evaluation value at the time when the in-focus state is reached is stored, the focus evaluation value is always calculated even after the focus is obtained, the focus evaluation value is compared with the stored evaluation value, and the preset threshold value ( When this also falls below a fixed value), it is determined that the subject has moved and the focus operation is restarted.

As described above, by performing the focus operation by comparing the focus evaluation value with various threshold values and performing the focus operation, it is possible to realize an autofocus mechanism having high accuracy and excellent stability.

On the other hand, a normal video camera is equipped with a zoom mechanism. In this zoom mechanism, it is generally known that the depth of field varies depending on each zoom region, that is, the position of the zoom lens, which is a variable power lens, between the telephoto (Wide) and the telephoto (Wide). . That is, if the zoom is wide-angle, the depth of field is deep, and if the zoom is telephoto, the depth of field is shallow. Here, the depth of field is deep means that the in-focus state can be easily maintained even if the subject moves slightly back and forth from the point of focus,
If the depth is shallow, it means that it is difficult to maintain the focused state.

That is, when the same subject is imaged, the telephoto (Tel
e) area, wide-angle area (Wide) and middle area between them
The relationship between the focus evaluation value and the position of the focus lens changes as shown in FIG. 17 according to each area.

(C) Problems to be solved by the invention Therefore, as described above, the focus evaluation value and its drop are compared with various reference values, and an autofocus mechanism for always fixing the focus lens at the maximum point is provided. When the above zoom mechanism is used together, the drop in the focus evaluation value with respect to the constant displacement amount of the focus lens is small in the wide angle FIG. 17 and large in the telephoto FIG. 17 as described above. , If the reference value is a fixed value, that is, if the response characteristics of the focus motor to the focus evaluation value is fixed, it takes time to detect a drop in the focus evaluation value in the case of a wide angle compared to telephoto, and quick auto The focus operation becomes difficult.

(D) Means for Solving the Problems The present invention is characterized in that the response characteristic of the focus motor with respect to the focus evaluation value is changed according to the zoom area.

(E) Operation Since the present invention is configured as described above, a quick and stable autofocus operation can be performed regardless of the zoom area.

(F) Embodiment Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.

FIG. 2 is a view showing the structure of the zoom ring portion of the apparatus of this embodiment.

A zoom ring (52) that supports a variable magnification lens (zoom lens) (not shown) is rotatably arranged in the radial direction on the lens barrel portion (51) protruding forward of the video camera body. When the zoom motor (61) drives the (52) to rotate, the variable power lens moves back and forth in the optical axis direction, and moves to the telephoto side and the wide-angle side.

At the front end of the outer circumference of the zoom ring (52), there are first to third step portions (53a) (53b) (53c) having different amounts of forward projection.
The cam part (53) with the
Position detection switch so that the operating piece (54a) comes into contact with 3).
(54) is fixed to the lens barrel (51). The position detection switch (54) is of a three-stage switching type, and is switched to three stages by bringing the operating piece (54a) into contact with the first to third step portions (53a) (53b) (53c), respectively. . The output of the position detection switch (54) is supplied to a threshold value setting memory (60) described later, and signal processing is performed.

FIG. 1 is a circuit block diagram of the apparatus of this embodiment. lens
The image formed by (1) becomes a luminance signal by an image pickup circuit (4) having a CCD (image pickup element) and is input to a focus evaluation value generation circuit (focus evaluation value detection means) (5).

The focus evaluation value generating circuit (5) is constructed as shown in FIG. 4, for example. 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. Gate control circuit (5
In b), the vertical synchronizing signal (VD) and the horizontal synchronizing signal (H
D) and a fixed oscillator output, a rectangular sampling area is set in the central portion of the screen, and a gate opening / closing signal that allows passage of a luminance signal only in the range of this sampling area is supplied to the gate circuit (5c).

The gate circuit (5c) passes through the HPF (5d) only the luminance signal corresponding to the range of the sampling area, separates only the high frequency component, and the detection circuit (5e) at the next stage performs amplitude detection. This detection output is integrated for each field by an integrating circuit (5f) and converted into a digital value by an A / D conversion circuit (5g) to obtain a focus evaluation value of the current field.

(16) is a switch circuit, which is controlled by the switching control circuit (23), and when it is switched to the terminal (16a) side, it is output to the first focus motor control circuit (15) described later. The focus motor (3) is controlled and the terminal (16b)
When it is switched to the side, it is controlled by the output of the second focus motor control circuit (17) described later. Immediately after the start of the autofocus operation, it is switched to the terminal (16a) side.

Immediately after the start of the autofocus operation, the first focus evaluation value is held in the maximum value memory (10) and the initial value memory (11). After that, the first focus motor control circuit (15) rotates the focus motor (3) in a predetermined direction and monitors the output of the second comparator (13). The second comparator (13) compares the focus evaluation value after driving the focus motor with the initial evaluation value stored in the initial value memory (11), and outputs the magnitude.

The first focus motor control circuit (15) is connected to the second comparator (13).
Rotate the focus motor (3) in the first direction until the output is large or small, and if the output that the current evaluation value is larger than the initial evaluation value is made, rotate as it is. Direction, the current evaluation value is smaller than the initial evaluation value, the rotation direction of the focus motor (3) is reversed, and then the output of the first comparator (12) is monitored. It should be noted that the second comparator (13) does not generate a large or small output unless the difference between the initial evaluation value and the current focus evaluation value exceeds a predetermined value in order to prevent malfunction due to noise in the evaluation value. You may make it output the output that it is the same.

The first comparator (12) compares the maximum evaluation value up to now held in the maximum value memory (10) with the current evaluation value, and the current evaluation value is compared with the contents of the maximum memory (10). Large (first mode), the same or slightly smaller (second mode), and smaller than the content of the maximum value memory (10) so as to exceed the threshold value output from the threshold value setting memory (60) described later (first mode). Three different comparison results (3 modes) are output. Here, the maximum value memory (10) is updated based on the output of the first comparator (12) when the current evaluation value is larger than the content of the maximum value memory (10), and is always evaluated up to the present time. The maximum value is retained.

The first to third threshold values (N1) (N
2) (N3) is stored in advance and the position detection switch
(54) Based on the output, the three types of threshold value data described above are selectively output. That is, when the zoom ring (52) is located on the wide angle side and the operating piece (54a) is in contact with the first step portion (53a) and is in the first position shown by the solid line (A) in FIG. , The terminals (55) and (56) are conductive, and the input terminals (60a) and (60b) of the threshold setting memory (60) are supplied with the rotational position information of "H" and "L", respectively, and the threshold setting is performed in response to this. The memory (60) outputs the first threshold value (N1). When the zoom ring (52) rotates toward the telephoto side, which is the direction of arrow X in FIGS. 2 and 3, the operating piece (54a) slides on the cam portion (53) and the second step portion (53).
b), it moves to the second position shown by the dotted line (B) in FIG. 3, the terminals (56) (57) become conductive, and the input terminals (60a) (60b) of the threshold setting memory (60) Is supplied with the rotational position information of "H" and "H" respectively, and in response to this, the threshold setting memory (60)
Outputs a second threshold (N2). In addition, the zoom ring (5
When 2) rotates to the telephoto side, the operating piece (54a) contacts the third step portion (53c), moves to the first position shown by the dotted line (C) in FIG. 3, and the terminals (56) (57) are moved. When the threshold value setting memory (60) is turned on, rotational position information of "L" and "H" is supplied to the input terminals (60a) and (60b) of the threshold value setting memory (60).
(60) outputs the third threshold value (N3).

(14) 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 the maximum value memory (10) Similarly to the above, based on the output of the first comparator (12), the focus ring position when the maximum evaluation value is reached is updated so as to always be held.

The first focus motor control circuit (15) is connected to the second comparator (13).
While rotating the focus motor (3) in the direction determined based on the output, the output of the first comparator (12) is monitored, and in order to prevent malfunction due to noise in the evaluation value, the first comparator (12) )
At the output, the current evaluation value is higher than the maximum evaluation value.
(60) Third value that is small enough to exceed the output threshold
The focus motor (3) is rotated at the same time when the mode is designated.

The reverse rotation timing of this focus motor (3)
This will be described in detail with reference to FIGS. 14 to 16 are characteristic diagrams showing the relationship between the focus lens position and the focus evaluation value when the zoom is in the wide angle range, the intermediate range, and the telephoto range. When the zoom lens is on the wide-angle side, the depth of field becomes deeper, so that the fluctuation of the focus evaluation value with respect to the focus lens position becomes smaller, but the first threshold value output from the threshold setting memory (60) is set. Since (N1) is set to be extremely small, the distance (Δ) from the in-focus position (P) as shown in FIG.
l) It will be reversed at the point (Q) that has passed too much. When the variable power lens is between the wide angle and the telephoto, the second threshold value (N2) output from the threshold value setting memory (60) is set larger than the first threshold value (N1). Point that is too far from the in-focus position (P) by the distance (△ l)
It will be reversed at (Q '). When the zoom lens is on the telephoto side, the depth of field becomes shallow, so the focus evaluation value varies greatly with the focus lens position.
At this time, the third threshold value (N
Since 3) is larger than the first and second threshold values (N1) and (N2), it is necessary to reverse at the point (Q ″) which is too far from the in-focus position (P) by the distance (Δl) as shown in FIG. As described above, the first to third threshold values (N1) (N2) (N3) are set to N1.
By providing the relationship of <N2 <N3, even if the wide-angle range, the medium-angle range, the telephoto range and the zoom range are changed, the focus motor (3) is too far from the in-focus position by the distance (Δl). ) Can be reversed.

After this reverse rotation, the contents of the motor position memory (14) are compared with the current focus ring position signal by the fifth comparator (30), and when they match, that is, the focus evaluation value of the focus ring (2) Focus motor when returning to maximum position (3)
The first focus motor control circuit (15) functions to stop the. At the same time, the first focus motor control circuit (15) outputs a lens stop signal (LS).

The switching control circuit (23) receives the lens stop signal (LS), switches the switch circuit (16) to the terminal (16b) side, and thereafter outputs the second focus motor control circuit (17) to the focus motor. Control (3).

Next, the control by the second focus motor control circuit (17) will be described. This second focus motor control circuit
Since (17) is composed of a microcomputer,
The internal operation is as shown in the flow chart of FIG.

First, the rotation direction of the focus motor (3) is initialized, the focus motor (3) is switched to a preset rotation direction for the time being, and the rotation direction is maintained inside (procedure (a )). After that, the current focus evaluation value is set to the third
It is held in the memory (19) as a reference value (procedure (b)). Then, the focus motor (3) is rotated by a small amount in the retained direction (procedure (c)). Along with this rotation, the lens (1) is displaced by a small amount (ΔT) (ΔT: 1 unit) in the initially set direction. After this displacement, the third comparator (1
In step 8), the current focus evaluation value is compared with the reference value stored in the third memory (19) (procedure (d)). If the current evaluation value is smaller, it is stored internally now. It is displaced by 2 units in the opposite direction to the minute displacement direction (procedure (e)). Here, the third comparator (18) again compares the reference value of the third memory (19) with the current focus evaluation value (procedure (f)). If the current evaluation value is smaller, the comparison is performed again. The focus motor (3) rotates so as to reverse the displacement direction and return by one unit (procedure (g)). In other words, in this case, the lens is slightly displaced from the lens position stopped by the autofocus operation by the first focus motor control circuit (15) so as not to affect the image in the front and back, and the lens is stopped first. After confirming that the focus evaluation value at the lens position which has been set is the maximum, the lens is returned to the original stop position and the state becomes the standby state.

The movements of the focus motor (3) and the lens (1) at this time are shown in FIGS. 6 and 7. Here, in FIG. 6, the vertical axis represents the initialized rotation direction and the horizontal axis represents time. In FIG. 7, the vertical axis represents the focus evaluation value, and the horizontal axis represents the lens position (distance between the lens and CCD). The small displacement amount (ΔT) is extremely small compared to the displacement of the lens by the first focus motor control circuit (15) and does not affect the image.

Next, a case where the lens position stopped by the first focus motor control circuit (15) is slightly deviated from the maximum point will be described.

After the lens is stopped by the first focus motor control circuit (15), the second focus motor control circuit (17) initializes the rotation direction of the focus motor (3) in the same manner as described above and holds the direction to move. Then, the reference value of the third memory (19) is updated, the focus motor (3) is slightly rotated in the holding direction to displace the lens (1) by one unit, and the current focus evaluation value and the reference value are compared. As a comparison, the stop point by the first focus motor control circuit (15) is deviated from the maximum point of the focus evaluation value. Therefore, either one of the focus evaluation values is slightly displaced from the stop point in the positive or negative direction. Becomes larger than the standard value. Therefore, the comparison result of any of the procedures (d) and (f) in FIG. 5 becomes "NO", and the procedure shifts to the procedure (h). In the comparison of the procedure (h), "YES" corresponds to the case where the stop point is largely deviated from the maximum point as described later, and "N" is initially set.
Select “O” and return to (A). Here, the value of the third memory (19) is set with the focus evaluation value at this position as the reference value, with the minute displacement point having the evaluation value larger than the stop point as the reference. Updated,
The above operation is repeated. By repeating this, the deviation between the stop point and the maximum point of the focus evaluation value by the first focus motor control circuit (15) is corrected. The movements of the focus motor (3) and lens (1) in this case are shown in FIGS.
Shown in Figure 1.

8 and 9 show the case where the evaluation value becomes large in the initialized direction, and the maximum point is reached when the lens position is separated from the CCD by 2 units (displaced in the right direction in the figures). , STEP (3) to (5) are STs of FIGS. 6 and 7.
The operation is the same as EP (1) to (3). Further, FIGS. 10 and 11 show the case where the evaluation value becomes large in the opposite direction from the initialization, and the lens position approaches the CCD by two units (displaces to the left in the figure). As a result, the maximum point is reached, and STEPs (4) to (6) have the same operations as those in FIGS. 6 and 7 although they have opposite polarities.

As described above, the lens (1) also reaches the maximum point of the focus evaluation value by the second focus motor control circuit (17), but only a small displacement can be made at one time so as not to affect the screen. When the stop point by the first focus motor control circuit (17) is largely deviated from the maximum point of the focus evaluation value, it takes time to correct the deviation, and a good autofocus operation cannot be expected.

Therefore, in step (h), it is determined whether or not the maximum point deviates from the stop point by a predetermined amount or more. That is, it is determined whether or not the correction by the minute displacement is performed N times or more, that is, whether or not the lens position is displaced by N units or more. Therefore, if you do not exceed N units in any direction from the first stop point by making a slight correction to the lens position as described above, jump to Fig. 5 (A) and set the current lens position as the reference value. Continue to fine-tune the focus.

However, if the lens (1) has moved more than N units in either direction from the first stop point in the judgment of the procedure (h), the second
The focus motor control circuit (17) outputs an out-of-focus confirmation signal, which is input to the switching control circuit (23) through the OR circuit (22). In FIGS. 12 and 13, first, the stop point is N (for example, N = N) in the direction in which the lens approaches the CCD rather than the maximum point.
6) The figure shows the case where there is a deviation of more than one unit.
The state where the loop of (A) → procedure (h) is repeated seven times is shown.

Upon receiving the unfocusing confirmation signal, the switching control circuit (23) switches the switch circuit (16) to the terminal (16a) side again, and replaces the second focus motor control circuit (17) with the first focus motor control. The focus motor (3) is controlled by the output of the circuit (15), and a rapid autofocus operation is performed by a large lens displacement.

(20) is a fourth memory which holds the focus evaluation value at that time at the same time as the lens stop signal (LS) is issued after the autofocus operation by the first focus motor control circuit (15) is completed. Yes, this fourth comparator (21)
The content of the memory (20) is compared with the current focus evaluation value,
When the difference becomes larger than a predetermined value (restart reference value), a subject change signal is output to the OR circuit (22) because the subject has changed. This signal is input to the switching control circuit (23) via the OR circuit (22), the switch circuit (16) is switched to the terminal (16a) side, and the first autofocus operation is redone to follow the change of the subject.

The second focus motor control circuit (17) controls the first
When it is confirmed that the stop point by the focus motor control circuit (15) is the maximum point, the focus motor (3) until the fourth comparator (21) determines that the subject has changed.
Will continue to stop, but if the second focus motor control circuit (17) confirms the maximum point intermittently at certain time intervals regardless of the comparison result by the fourth comparator (21). Needless to say, the certainty increases.

With the configuration described above, the first focus motor control circuit (15) performs a quick autofocus operation to stop the lens, and even if the lens stops at a position that is not in focus due to a sharp movement of the subject, When the lens position is finely adjusted by the second focus motor control circuit (17) and is largely deviated, the quick auto focus operation is restarted again by the first focus motor control circuit (15), and further the fourth focus Even when it is determined by the comparator (21) that the subject has changed, the control by the first focus motor control circuit (15) is redone. When the lens stops at the true focus, the lens movement is the second
Only a minute displacement by the focus motor control circuit (17) has a very small effect on the image.

Further, with the configuration as described above, the zoom area of the zoom lens can be detected by a simple mechanism, and even if the zoom area changes, the focus position can be detected quickly, which is useful.

In the above embodiment, the zoom area is set to TEL for convenience.
It is divided into three areas, E, WIDE, and MIDDLE. This area division is the resolution of the imaging optical system, the depth of focus, and the S / of the imaging circuit.
It will be apparent that it is also affected by the N ratio and is not necessarily limited to the above-mentioned embodiment.

(G) Effect of the Invention As described above, according to the present invention, the zoom position of the zoom lens in the autofocus video camera of the system in which the focus lens once passes through the in-focus point and then reverses and returns to the in-focus point. Irrespective of the above, it is possible to perform a stable autofocus operation that is always quick, has no malfunction, and has high focusing accuracy.

[Brief description of drawings]

1 to 16 relate to the first embodiment of the present invention.
Figure is a circuit block diagram, Figure 2 is a side view of the lens barrel,
FIG. 3 is an explanatory diagram of the position detection switch, FIG. 4 is a circuit block diagram of the focus evaluation value generating circuit, FIG. 5 is a flow chart, and FIGS. 6 and 7 are explanatory diagrams of focus confirmation operation. Figure,
FIGS. 9, 10, and 11 are explanatory views when the stop point is slightly deviated from the maximum point, and FIG. 12 and FIG. 13 are explanatory views when the stop point is greatly deviated, and FIGS. Fig. 1
FIG. 6 is a characteristic diagram of the focus evaluation value in the wide angle range, the intermediate range, and the telephoto range, and FIG. 17 is a characteristic diagram showing the change of the focus evaluation value with respect to the zoom ring position. (52) ... Zoom ring (zoom mechanism), (5) ... Focus evaluation value generation circuit (focus evaluation value detection means), (1) ... Focus lens, (3) ... Focus motor (focus lens displacement means) , (60) ... Threshold setting memory (response characteristic switching means),

Claims (1)

[Claims] 1. A focus evaluation value detecting means for detecting a high frequency component level of a luminance signal obtained from an image pickup device as a focus evaluation value, and a zoom position detection for detecting a zoom position of an image pickup zoom lens changing from a telephoto to a wide angle. Means, a focus motor that moves a focus lens based on the focus evaluation value, a motor position memory that stores a motor position of the focus motor when the focus evaluation value reaches a maximum value, and the focus evaluation value is maximum. A focus motor control circuit that reverses the focus motor when the value reaches a value once and then decreases by a preset threshold value, and the motor when the current motor position matches the value of the motor position memory when the focus motor reverses. And a means for stopping the above, and the threshold value is set large on the wide-angle side and small on the telephoto side. Autofocus video camera and means for switching in accordance with the zoom position.