JP3535603B2 - Automatic focusing device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focusing device used in various video cameras and the like.

[0002]

2. Description of the Related Art In recent years, video equipment such as a video camera has made remarkable progress, and auto focus control, auto iris control, zoom function, etc. are standard equipment.
In every part, the operability is improved and the functions are increased. Looking at the automatic focus adjustment device that performs the above-mentioned autofocus control, the sharpness of the screen is detected based on the video signal obtained by photoelectrically converting the subject by the image sensor, and the focus lens position is controlled so that it becomes maximum. By doing so, a method of performing focus adjustment is becoming mainstream. As a method of evaluating the sharpness, generally, the level (focus voltage) of the high frequency component of the video signal extracted by the band pass filter of a certain band is used. This is because, when a normal subject image is taken, as shown in FIG. 5, the level of the high frequency component (focus voltage) increases as the focus is adjusted, and the point at which the level becomes maximum is the in-focus position. Is the way.

FIG. 6 is a block diagram showing the structure of a conventional video camera which is adapted to perform autofocus control. In FIG. 6, 101 is a subject, 102 is a fixed first group lens, 103 is a variable magnification lens for changing the magnification, 104 is a diaphragm, 105 is a fixed second group lens, and 106 is a movement of the focal plane due to the variable magnification. It is a focus compensating lens (hereinafter referred to as a focus lens) that has both a function of correcting an image and a function of focusing. Further, 107 is a CC as an image sensor.
D and 108 are AGC circuits for amplifying the output of the CCD 107, and the amplification factor is controlled by a signal from a camera AF microcomputer 118 described later. Reference numeral 109 is a camera signal processing circuit, and reference numerals 110, 112 and 114 are variable magnification lenses 1 respectively.
03, the diaphragm 104, and actuators for moving the focus lens 106, and 111, 113, and 115 are drivers that drive the actuators 110, 112, and 114 by signals from the camera AF microcomputer 118, respectively. Reference numeral 116 denotes an AE evaluation value processing circuit that obtains an integrated value of a video signal level used for controlling the diaphragm 104 and the AGC circuit 108 by using the output signal level of the CCD 107.
Reference numeral 117 denotes an AF evaluation value processing circuit for extracting a high frequency component used for focus detection from the output signal of the image sensor 107, 118
Controls the entire system, and based on the output signals of the AE evaluation value processing circuit 116 and the AF evaluation value processing circuit 117, the actuators 110, 112, 1
14 and the AGC 108 are camera AF microcomputers.

In the camera system configured as shown in FIG. 6, the camera AF microcomputer 118 opens and closes the aperture 104 and the amplification factor of the AGC circuit 108 so that the output signal level of the AE evaluation value processing circuit 116 becomes a constant value. By controlling and, automatic exposure adjustment is performed. Further, automatic focus adjustment is performed by moving the focus lens 106 in the optical axis direction so that the output signal level of the AF evaluation value processing circuit 117 becomes maximum.

Next, the control processing of the camera AF microcomputer 118 will be described with reference to the flowcharts of FIGS. First, the AF process will be described generally with reference to FIG. In step S501, the AF evaluation value is fetched from the AF evaluation value processing circuit 117. In step S502, the current AF mode is determined. If the AF mode is the restart determination mode, restart determination processing is performed in step S503. If it is the direction determination mode, the direction determination process is performed in step S504. In the mountain climbing mode, a mountain climbing process is performed in step S505. The contents of each processing of these steps S502, S503, and S504 will be described below.

FIG. 8 shows the processing in the restart determination mode. First, in step S601, step S70 of FIG.
In step 5, the holding value held during the transition to the restart determination mode is compared with the AF evaluation value. If the difference between the holding value and the AF evaluation value is larger than the predetermined value in step S602, the process proceeds to step S603 and the direction determination mode is entered. Then, the process ends.
If the difference between the held value and the AF evaluation value is not larger than the predetermined value, the process ends.

FIG. 9 shows the processing in the direction determination mode. First, in step S701, wobbling is performed in which the focus lens is oscillated back and forth to determine whether it is in-focus or out-of-focus. In step S702, it is determined whether the determination is completed. If not completed, the process ends. If the determination is completed, it is determined in step S703 whether or not it is in focus, and if it is in focus, the process proceeds to step S704, shifts to the restart determination mode, and the next step S705.
Then, the AF evaluation value is held as the restart holding value, and the process ends.
If it is out of focus in step S703, the mode shifts to the hill climbing mode in step S706, the AF evaluation value is held as an initial value for hill climbing in step S707, and step S701.
Climb in the direction determined by.

The wobbling in step S701 will be described with reference to FIG. This is because the focus lens 106 is moved by a predetermined movement amount as shown in FIG. 11, and every time the focus lens 106 is moved, the AF evaluation value at the previous focus lens position and the AF evaluation value at the current focus lens position are compared, If the AF evaluation value of 1 is large, the focus lens 106 is moved in the same direction a as it is, and if it is small, the focus lens 106 is moved in the direction in which the AF evaluation value is always large by moving the focus lens 106 in the reverse direction b. If there is a high probability that the focus lens 106 will move to either the closest direction or the infinite direction, the mode shifts to the hill climbing mode in that direction. On the other hand, when the focus lens 106 reciprocates within a certain range, it is determined that the focus lens 106 is in focus, and the restart determination mode is entered.

FIG. 10 shows the processing in the mountain climbing mode. First, in step S801, the peak hold of the AF evaluation value is performed. If the AF evaluation value is larger than the current peak value, this value is newly set as the peak value and the focus lens position is saved. Next, step S8
In 02, it is determined whether or not the AF evaluation value is larger than the initial value for hill climbing held in step S707. If so, it is determined in step S803 whether the AF evaluation value is smaller than the peak value. If the AF evaluation value is not smaller than the peak value, the process ends.

If the AF evaluation value is smaller than the peak value, a process of returning to the focus lens position of the peak value is performed in step S804, it is determined in step S805 whether or not the focus lens position of the peak value has been returned, and if it is returned, step S806. Press to move to the direction determination mode. If not returned, the process ends. If the AF evaluation value is smaller than the initial value for hill climbing in step S802, the hill climbing direction is reversed to drive the focus lens in the opposite direction in step S807, and the initial value for hill climbing is set to the current AF value in step S808.
Update to the evaluation value. In this way restart judgment → direction judgment →
The camera AF microcomputer 118 controls so that the AF evaluation value is always maximized by moving the focus lens while repeating mountain climbing → direction determination → restart determination.

FIG. 12 shows a drive mechanism for the focus lens 106. Reference numeral 114 is a focus competition lens motor for driving the lens, 301 is a rotation shaft of the motor 114, and 302
Is a rack that moves via the rotation shaft 301 by the rotation of the motor 114, to which the focus lens 106 is attached.

[0012]

However, the above-mentioned conventional example has the following problems. Focus lens 1
When moving 06 by a predetermined amount of movement, even if the motor 114 is rotated by a certain amount due to rattling of the rotating shaft 301 and the rack 302 in FIG.
In some cases, the lens does not move by the movement amount according to the rotation amount of the motor 114, as indicated by C. In recent years, the image pickup surface of the CCD has become smaller and the influence of the focus lens position error on the focus has been significantly increasing. However, the amount of movement of the focus lens 106 cannot be ensured due to the play described above.
For this reason, a highly accurate AF evaluation value cannot be obtained, which may cause an erroneous determination of the direction of the focus lens 106.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to obtain an automatic focus adjusting device capable of obtaining an in-focus point with high accuracy regardless of rattling of a lens driving mechanism. .

[0014]

SUMMARY OF THE INVENTION An automatic focus adjusting device of the present invention is an automatic focus detecting device for controlling the position of a focus lens based on an output signal of an image pickup device, wherein the focus lens is focused based on the output signal. AF evaluation value detecting means for detecting an AF evaluation value indicating a state, lens driving means for moving the focus lens in the optical axis direction, and the focus lens based on the AF evaluation value detected by the AF evaluation value detecting means. And a control means for controlling the lens driving means to move the lens by a predetermined movement amount, and if the AF evaluation value by the AF evaluation value detecting means is decreased, the moving direction of the focus lens is reversed and The feature is that the focus direction and focus of the focus lens are determined after the additional movement amount is added to the predetermined movement amount to move the focus lens. Having.

[0015]

[0016]

[0017]

[0018]

[0019]

EXAMPLE A first example of the present invention will be described below. A video camera to which the present invention is applied has the same configuration as that shown in FIG. Next, the control processing of the camera AF microcomputer 118 according to the present invention will be described with reference to FIG. This FIG. 2 shows step S7 of FIG. 9 in the conventional example.
1 shows wobbling with 01.

First, in step S1, a predetermined amount of wobbling movement is determined. Next, in step S2, the AF evaluation value is compared with the previous AF evaluation value at the focus lens position. Next, if the AF evaluation value has increased in step S3, the process jumps to step S6. If the AF evaluation value has decreased in step S3, the moving direction of the focus lens 106 is reversed in step S4. Next, in step S5, a predetermined additional movement amount is added to the movement amount determined in step S1.
After that, the direction is determined in step S6, the focus is determined in step S7, and the process ends.

As described above, by adding the additional movement amount at the time of reversing the focus lens, the movement amount of the lens cannot be ensured at the time of reversing as in the conventional case, and a sufficient change in the AF evaluation value cannot be obtained, and the direction determination is not erroneous. It is possible to realize highly accurate focus adjustment.

Next, a second embodiment of the present invention will be described. FIG. 3 shows the cam locus of the rear focus lens. In this figure, the horizontal axis represents the zoom lens position and the vertical axis represents the focus lens position. As can be seen from FIG. 3, it is understood that the required movement amount of the focus lens with respect to the change in the subject distance is different between the zoom position at the tele end and the wide end. This Figure 3
Based on the above, the amount of movement at the time of direction determination is currently large on the tele end side and small on the wide end side. Therefore, on the tele end side, the original movement amount is larger than the amount of backlash between the rack 302 and the rotary shaft 301, and it is not necessary to add the additional movement amount.

FIG. 4 shows the control processing of the camera AF microcomputer 118 according to the second embodiment. FIG. 4 shows wobbling in step S701 of FIG. 9 in the conventional example, and steps S1 to S7 correspond to FIG. Here, step S4a is added between steps S4 and S5. In FIG. 4, if the AF evaluation value has decreased in step S3, it is reversed in step S4. Next, in step S4a, it is determined whether the zoom lens position is near the wide end. If it is not near the wide end, step S5
And skip to step S6. If it is near the wide end, the process proceeds to step S5, and the additional movement amount is added to the movement amount determined in step S1. After that, the direction is determined in step S6, and the focus is determined in step S7, and the process ends.

As described above, by adding the additional movement amount when the focus lens is reversed, it is possible to realize highly accurate focus adjustment as in the first embodiment. Further, by prohibiting addition of an additional movement amount according to the focal length, it is possible to prevent the lens from being moved more than necessary at a zoom position where it is not necessary to add an additional movement amount, and to realize focus adjustment without flicker. be able to.

FIG. 1 is a block diagram conceptually showing the present invention. In FIG. 1, reference numeral 1 denotes a lens, which includes a focus lens or a focus lens and a zoom lens. 2 is C
Imaging means including a CD, 3 is an AF evaluation value detecting means, 4 is a control means for performing autofocus control, 5 is a lens driving means for moving the lens 1 back and forth in the optical axis direction, and 6 is a lens 1.
Inversion detection means for detecting that the image is inverted from one direction to the opposite direction, 7 is change means for changing the movement amount of the lens 1 according to the inversion detection, 8 is a focal length detection means for detecting the focal length of the lens 1, Reference numeral 9 is a prohibiting means for prohibiting the change of the movement amount according to the prohibited focal length.

Next, the operation of the above configuration will be described. The subject image is picked up by the image pickup means 2 through the lens 1. The AF evaluation value detection means 3 extracts the level of the high frequency component from the imaged image signal, and supplies this to the control means 4 as an AF evaluation value. The control means 4 controls the lens driving means 5 in order to reciprocate the lens 1 by a predetermined movement amount so that the AF evaluation value becomes the maximum value,
As a result, the lens 1 is controlled to climb the mountain aiming at the focal point.

In this control, when the reversal detecting means 6 detects that the lens 1 is reversing, the changing means 7 changes the moving amount by adding the additional moving amount to the predetermined moving amount by the lens driving means 5. .

Further, the focal length detecting means 8 detects whether or not the focal length of the lens 1 is near the wide end, and if it is not near the wide end, the prohibiting means 9 prohibits the changing means 7 from changing the movement amount.

[0029]

As described above, according to the first aspect of the present invention, if the AF evaluation value is decreased, the moving direction of the focus lens is reversed and the movement amount calculated based on the AF evaluation value is set. After the additional movement amount is added and the focus lens is moved, the focus direction and focus of the focus lens are determined. Therefore, the movement amount of the focus lens can be secured during inversion, and highly accurate focus adjustment can be realized. it can.

Further, according to the second aspect of the present invention, since the additional movement amount is not added according to the focal length, the focus lens is not moved more than necessary at the zoom position within a certain range, and a feeling of fluttering occurs. No focus adjustment can be achieved.

Further, according to the third aspect of the present invention, the additional movement amount is not added when the focal length is not closer to the wide side, so that the movement amount of the focus lens is increased at the tele end side. You can avoid moving it more than necessary.

[Brief description of drawings]

FIG. 1 is a block diagram conceptually showing the present invention.

FIG. 2 is a flowchart showing a first embodiment of the present invention.

FIG. 3 is a graph showing a cam locus of a rear focus lens used in a second embodiment of the present invention.

FIG. 4 is a flowchart showing a second embodiment.

FIG. 5 is a graph showing the relationship between focus lens position and focus voltage.

FIG. 6 is a block diagram showing a configuration of a video camera to which the present invention can be applied.

FIG. 7 is a flowchart showing AF mode determination.

FIG. 8 is a flowchart showing restart determination.

FIG. 9 is a flowchart showing direction determination.

FIG. 10 is a flowchart showing a mountain climbing mode.

FIG. 11 is a graph for explaining wobbling.

FIG. 12 is a side view of a lens driving mechanism.

FIG. 13 is a graph for explaining the lens movement when there is rattling between the rotation shaft of the motor and the rack.

[Explanation of symbols]

1 lens 2 Imaging means 3 AF evaluation value detection means 4 Control means 5 Lens drive means 6 Inversion detection means 7 Change means 8 Focal length detection means 9 prohibition measures

Claims (3)

(57) [Claims] 1. An automatic focus detection device for controlling a focus lens position based on an output signal of an image pickup device, wherein an AF evaluation value detection for detecting an AF evaluation value indicating a focus state of the focus lens based on the output signal. Means, lens driving means for moving the focus lens in the optical axis direction, and the lens driving means for moving the focus lens by a predetermined movement amount based on the AF evaluation value detected by the AF evaluation value detecting means. If the AF evaluation value by the AF evaluation value detecting means is decreased, the moving direction of the focus lens is reversed and an additional moving amount is added to the predetermined moving amount. An automatic focus adjustment device, characterized in that the focus direction and focus of the focus lens are determined after the movement. 2. A focal length detecting means for detecting the focal length of the focus lens is provided, and the additional movement amount is not added according to the focal length detected by the focal length detecting means. The automatic focusing device described in. 3. The automatic focusing apparatus according to claim 2, wherein the additional movement amount is not added when the detected focal length is not closer to the wide side.