JPH0820591B2 - Automatic focus adjustment device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video camera or an automatic focus adjusting device for a camera, and more particularly to an automatic focus adjusting device for preventing hunting which is likely to occur when a subject including a repeating pattern is photographed. Regarding

(Prior Art) A focus detection method called a phase difference method has been put into practical use in video cameras and autofocus (AF or automatic focus adjustment) of cameras. In this method, the subject light flux from the shooting lens is divided into light from the upper half and light from the lower half of the shooting lens, and the light is received by different light receiving elements. When the light is in focus, the upper light beam is received. The output of the light receiving element and the output of the light receiving element receiving the lower ray coincide with each other, but when they are out of focus, a phase shift occurs in the output of each light receiving element. The amount of phase shift can be detected, and the defocus amount of the photographing lens can be obtained using a predetermined arithmetic expression based on this amount of shift. Further, since the upper light ray and the lower light ray of the taking lens are switched before and after the focus, the defocus direction (front focus or rear focus) can be detected by utilizing this property.

Well, some methods are known for the phase difference method,
As one of them, the TC developed by Honeywell in the US is shown in Fig. 7.
The L (Through Camera Lens) method is shown. In the figure, 1
Is a photographing lens, 2 is an infrared cut filter, 3 is a correction lens, 4 is a light shielding plate, 5 is a microlens array, and 6 is a CCD (Charge Co) arranged behind the microlens array 5.
upled Device). The exit pupil of the taking lens 1 and the light receiving surface of the CCD 6 are in a conjugate relationship, and the upper half of the exit pupil is
The light receiving element of row A of CCD6 is configured so that the light receiving element of row B can see the lower half. At the time of focusing, the output signal from the A-row light receiving element of the CCD 6 and the output signal from the B-row light receiving element coincide with each other, but when they are out of focus, a deviation occurs between the two output signals as shown in FIG. The shift amount S is obtained by an operation called HF logic described below using a microcomputer (see Japanese Patent Laid-Open No. 57-45510).

Here, a _i and b _i are the outputs of the i-th row A light receiving element and the B row light receiving element of the CCD 6, respectively. Addition value V _{j in} equation (1)
Is plotted for j = -12 to 12 as shown in FIG. 9, and V _k >
0, V _{k + 1} <interpolating the shift amount S is obtained between 0 and a and V _k and V _{k + 1} determine the k for V _k and V _{k + 1} of the difference D _e is maximized by: .

The difference V _k −V _{k + 1 at} this time has a correlation with the contrast of the detected image, and is also used for contrast determination during AF processing.

The shift amount S obtained as described above is converted into a shift amount (defocus amount) between the imaging position of the photographing lens and the image pickup element surface of the video camera, and the photographing lens 1 is focused according to the defocus amount. Move to the position by the focus motor.

By the way, when the subject of the video camera has a repetitive pattern such as a building with windows of the same shape or a lattice pattern, the added value V _{j of the} equation (1) is plotted in the graph as shown in FIG. , V _k and V _{k + 1} have a maximum difference D _{e at a} plurality of points (points a and b in the figure). That is, even if only one maximum value of V _k −V _{k + 1} (D _e ) is detected in one calculation, in the case of a subject having a repeating pattern, a slight fluctuation of the output signal of the light receiving element causes
The position where V _k −V _{k + 1} (D _e ) becomes maximum changes, and the focus position changes at each detection. For this reason, a hunting phenomenon occurs in which the photographing lens is repeatedly driven back and forth by the focus motor, resulting in an unnatural operation.

This is a principle problem common not only to the focus detection method by the TCL method described above but also in the focus detection apparatus by the phase difference method.

(Object and Structure of the Invention) The present invention has been made in view of the above points, and in a focus detection device for a camera using a phase difference method, a smooth AF operation without causing hunting even when a subject includes a repeated pattern or the like. The purpose is to be able to.

In order to achieve this object, in the present invention, the first
As shown in the figure, it is determined whether or not there are a plurality of points that can be determined as the focus point based on the calculation value of the calculation means. It was configured to stop driving.

(Example) The present invention will be described below with reference to the drawings.

FIG. 2 is a block diagram of a video camera equipped with an automatic focusing device according to the present invention. In the figure, 7 is a focusing lens for focusing, and 8 is a focusing lens 7 moved in the optical axis direction. A focus motor, 9 is a drive circuit for driving the focus motor 8, 10 is a zoom lens for changing the magnification of the subject image, 11 is a zoom motor for rotating the zoom ring (not shown) to move the zoom lens 10, and 12 is Drive circuit for zoom motor 11, 13 is zoom lens
A position sensor for detecting the position of 10 and a master lens 14 for forming a subject image on the image sensor 15. The subject light flux is guided to the focus detection optical system by the half mirror 16 and imaged on the CCD 19 by the AF lens 17 and the microlens 18. Furthermore, 20 is a CCD driver that drives the CCD 19, 21 is a CC driver.
An A / D converter that converts the analog output from the D19 into a digital value, and 22 is an interface between the CCD driver 20 and the A / D converter 21 and the microcomputer (microcomputer) 23.

The microcomputer 23 obtains the shift amount S using the above-mentioned HF logic, and calculates the defocus amount from the shift amount S. By comparing the defocus amount with a preset focusing range, it is possible to determine whether the object is in focus, in focus, or in focus. At the front pin, a signal is output from the microcomputer 23 to the drive circuit 9,
The focus motor 8 is driven and the focusing lens 7 is moved in the retraction direction for a time period corresponding to the previously calculated defocus amount. On the other hand, in the case of the rear focus, a signal is output from the microcomputer 23 to the drive circuit 9 and the focusing lens 7 is moved in the extending direction.

Next, the operation of the automatic focusing apparatus according to the present invention will be described with reference to the flowchart of FIG.

First, when the CCD driver 20 is driven by a command from the microcomputer 23, the charge accumulation of the CCD 19 is started (F-1), and C
The output signal from the CD 19 is converted into a digital value by the A / D converter 21 and input to the microcomputer 23 (F-2). The microcomputer 23 obtains the shift amount S using the HF logic described above, and calculates the defocus amount from the shift amount S (F-3).
At this time, V _k out of V _k calculated by the above equation (1), V _k > 0, V
There are several places where _{k + 1} <0, and V _k and V _{k + 1}
The difference D _e between the values of
If it is larger than 256), it is judged that there are several points that can be judged as the focal point. When there are several points that can be determined as the focal point, an unnatural motion such as hunting may occur, and it is necessary to use this as an index for special processing. Therefore, it is determined whether or not there are two or more _{Des that} are equal to or greater than a predetermined value (F-4). If there are two or more, there is a possibility of hunting, so the microcomputer 23 issues a command to the drive circuit 9, The focus motor 8 is stopped (F-5). If there is one D _{e that} is equal to or greater than the predetermined value, the focus motor 8 is driven based on the calculated value obtained in step (F-3) to move the focusing lens 7 to the focusing position (F-6), and thereafter. Advances the flow to the next stage. In short, in this embodiment, the focus motor 8 is stopped when two or more D _e having a predetermined value or more are detected, and when the D _e becomes one, the focus motor 8 is driven again to move the focusing lens 7. That is why.

By doing so, the focus motor 8 is stopped when there are two or more D _{e that} are equal to or greater than the predetermined value, so that the hunting phenomenon does not occur even in the case of a subject having a repeating pattern.

FIG. 4 is a flow chart showing the operation of the second embodiment of the present invention.

In the embodiment shown in FIG. 3, the focus motor 8 is immediately stopped when two or more D _{e that} are equal to or more than a predetermined value are detected. However, even in such a case, when the focusing lens 7 is moved several times, the focus is brought into focus. There is. Therefore, in this embodiment, when two or more D _e having a predetermined value or more are detected, a predetermined number of times (for example, 5
The focus motor 8 is driven only once) and then stopped.

FIG. 4 shows the operation, and steps (F-
1) to (F-4) are the same as those in the embodiment shown in FIG. However, if there are two or more D _{e that} are greater than or equal to the specified value, check whether the motor stop flag is set (F-
5) If the flag is not set, the flag is set (F-6). If the flag is already set, the count value of the motor stop counter is checked (F-7). This counter has an initial value set to "5" and is decremented by 1 each time the focus motor 8 operates. If the count value of the counter is "0", the focus motor 8 is stopped (F-8),
If it is not "0", decrement the counter (F-
9), the focus motor 8 is driven according to the defocus amount obtained in step (F-3).

If there are no more than two D _e equal to or more than the predetermined value, it is not necessary to stop the focus motor 8, the motor stop flag is reset (F-11) and the counter is set to the initial value "5" (F-12). The focus motor 8 is driven (F-
Ten).

According to this embodiment, the focal point may be reached while driving the motor several times.

Next, FIG. 5 shows a part of the flow chart of the third embodiment. Other parts are the same as in FIG. In this embodiment, when the value is equal to or more than a predetermined value and D _e is two or more, the motor stop flag is not immediately set, but the calculated defocus amount and the history of the direction are stored in the memory of the microcomputer 23. The focus motor 8 is stopped according to the history. The microcomputer 23 is HS as described above.
The front pin and the rear pin can be judged from the calculation result of the logical expression,
When the calculated value of the rear pin is output after the calculated value of the front pin or vice versa, that is, when the front pin rear pin information is input, it may be determined that hunting is actually occurring.

Therefore, the microcomputer checks whether or not the front and rear pin information has been entered.
23 determines (F-13), if it is on, the motor stop flag is set (F-6), and if it is not on, step (F)
Go to -10) and drive the focus motor 8.

In the first embodiment (see FIG. 3), the focus motor 8 is stopped when two or more D _e having a predetermined value or more are detected, so the focus motor 8 is stopped even when hunting does not actually occur. However, according to this embodiment, the focus motor 8 is stopped after hunting actually occurs. Further, since the focus motor 8 is driven immediately several times instead of being stopped immediately, the effect of the second embodiment is obtained in that the hunting may be stopped during that time to reach the in-focus position.

By the way, when the focus motor 8 is driven, an overshoot may occur in which the motor 8 is driven beyond the focus amount calculated due to variations in the size of the drive system, but according to the third embodiment. This overshoot may cause the condition to be satisfied and the focus motor 8 to stop. However, even if an overshoot occurs, if it is near the in-focus point, there is a high possibility that it will stop at the in-focus position without causing hunting.

Therefore, in the fourth embodiment shown in FIG. 6, when the pre-focusing / post-focusing information is entered (F-13), it is next determined whether or not the defocus amount is within a predetermined value in the vicinity of focusing ( F-
14) If the value is not within the predetermined value, the motor stop flag is set (F-6), but if it is within the predetermined value, it is considered that the in-focus position is reached without causing hunting. It was made to drive (F-10). In this case, the predetermined value near the focus is set according to the resolution of the sensor, the magnification of the AF optical system, the controllability of the motor, or the like. The other part of the flow chart of this embodiment is the fourth part.
It is similar to the figure.

Although the video camera is taken as an example in the above-mentioned embodiment, the present invention is not limited to this and can be applied to a general still camera. Further, the focus detection method is not limited to the TCL method and can be applied to other known phase difference methods.

(Effects of the Invention) As described above, in the present invention, it is determined whether or not there are a plurality of points that can be determined as the focus point based on the calculation value of the calculation means. Since the drive of the focus motor is stopped by the stopping means, smooth AF without hunting occurs even when the subject contains repeated patterns.
You will be able to operate.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of an automatic focusing apparatus according to the present invention,
FIG. 2 is a block diagram showing an embodiment of the automatic focusing apparatus according to the present invention, FIG. 3 is a flow chart showing the operation of the embodiment of FIG. 2, and FIGS. 4 to 6 are other embodiments. The flowcharts shown in FIGS. 7 to 10 are explanatory views of the principle of the TCL system. 1 ... Shooting lens, 6, 19 ... CCD, 14 ... Master lens, 15 ... Image sensor

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location G03B 3/00 A

Claims (2)

[Claims] 1. A calculation means for forming two types of subject images on an image sensor, and calculating the defocus amount and direction of a photographing lens based on the phase difference between these two types of image signals. In the automatic focus adjusting device for moving the photographing lens to the in-focus position by using the focus motor based on the calculated value of the means, whether there are a plurality of points which can be determined as the focused point based on the calculated value of the calculating means. The automatic focus adjusting device is characterized by further comprising: a determination unit that determines whether or not there is a plurality of points that can be determined as the in-focus point by the determination unit, and a stop unit that stops the drive of the focus motor. . 2. The calculation means outputs a calculation value of a front pin or a rear pin, drives the photographing lens based on the calculation value of the calculation means, and then the calculation means follows the front pin and rear pins. 2. The automatic focus adjusting device according to claim 1, wherein the stop means stops the drive of the focus motor when the calculated value of the front pin is output following the rear pin. .