JPH01134317A - Automatic focus adjusting device - Google Patents

Abstract

PURPOSE:To perform AF operation without causing any hunting even when an object contains a repetitive pattern, etc., by stopping a focus motor from being driven when it is decided that there are points which can be judged as a focusing point according to the arithmetic value of an arithmetic means. CONSTITUTION:Object luminous flux is guided to a focus detection optical system through a half-mirror 16 to form two kinds of subject images on an image sensor, and the quantity of the deviation between those two kinds of image signals is found by a microcomputer 23 to calculate the quantity and direction of defocusing from the deviation quantity. A decision means decides whether or not there are plural points which can be judged as the focusing point according to this arithmetic value and when so, there is the possibility of natural operation such as hunting, so the microcomputer 23 sends a command to a driving circuit 9 to stop the focus motor 8. Therefore, no hunting phenomenon is generated even in case of an object having a repetitive pattern.

Description

Detailed Description of the Invention (Industrial Application Field) Unexploded IJl is an automatic focus adjustment device for a video camera or a camera, especially an automatic focus adjustment device designed to prevent hunting that is likely to occur when photographing a subject that includes a repetitive pattern. Regarding equipment.

(Prior Art) A focus detection method called a phase difference method has been put into practical use in autofocus (AF or automatic focus adjustment) of video cameras and cameras. In this method, the subject light flux from the photographic lens is divided into light from the upper half of the photographic lens and light from the lower half, and each light is received by a different light receiving element, and when the focus is on, the light from the upper half is received Either the output of the light-receiving element and the output of the light-receiving element receiving the lower light beam match, or a phase shift occurs in the outputs of the respective light-receiving elements when the light is out of focus. The amount of phase shift can be detected, and the amount of defocus of the photographing lens can be determined based on this amount of shift using a predetermined arithmetic expression. Furthermore, since the upper and lower rays of the photographic lens are switched before and after the focal point, this property can be used to detect the direction of defocus (front focus or rear focus).

Now, there are several known phase difference methods, and one of them, as shown in Figure 7, is the T
CL (Through Camera Lens)
Show the method. In the figure, l 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 (ChargeCoupled) placed behind the microlens array 5.
Device). Exit pupil of photographic lens L and C
It has a conjugate relationship with the light-receiving surface of the CD 6, so that the upper half of the exit pupil is viewed by the A-row light-receiving elements of the CCD 6, and the lower half is viewed by the B-row light-receiving elements. When in focus, the output signal from the A-row light receiving element and the output signal from the B-row light receiving element of the CCD 6 match, or when out of focus, there is a shift between the two output signals as shown in FIG. This deviation amount S is determined by a calculation called HF logic shown below using a microcomputer (see Japanese Patent Laid-Open No. 57-45510).

-=1◆Top--22-1j=1 Here, a I + b+ are i#[I
These are the outputs of the A-row light-receiving elements and the B-row light-receiving elements.

Addition value VJ of equation (1) is calculated as 9th for j=-12 to 12.
Plot as shown in the figure, V k > O, V k-+ <0
Find k for which the difference between vk and vl, 1 is maximum, and interpolate between V and V k + 1 using the following formula, and the deviation S is obtained.
Find out.

The difference Vh-Vi+++ at this time has a correlation with the contrast of the detected image, and is also used for contrast determination during AF processing.

The amount of deviation S obtained as above is converted into the amount of deviation (defocus amount) between the imaging position of the photographing lens and the imaging element surface of the video camera, and the photographing lens L is focused according to this amount of defocus. Move to the desired position using the focus motor.

By the way, if the subject of the video camera has a repeating pattern, such as a building with windows of the same shape or a lattice pattern, the sum VJ of equation (1) can be plotted on a graph as shown in Figure 10. There are multiple points where the difference between Vk and Vk*1 can be maximum (a in the figure,
point b). That is, for one (7) operation: 8 ite V k
Even if the maximum value of -V h -r (D -) is detected at one point, in the case of a subject with a repetitive pattern, Vh
The position where -Vk-* (D-) is maximum changes, and the focal position changes with 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 unnatural operation.

This is a fundamental problem not limited to the focus detection method using the TCL method described above, but common to focus detection devices using the phase difference method.

(Objective and Structure of the Invention) The present invention has been made in view of the above-mentioned points, and is a focus detection device for a camera using a phase difference method, which can smoothly capture images without causing hunting even when the subject includes a repetitive pattern. The purpose is to enable AF operation.

In order to achieve this object, the present invention, as shown in the overall configuration in FIG. When it is determined that there are a plurality of focus motors, the stop means is configured to stop driving the focus motor.

(Example) The present invention will be explained below based on the drawings.

FIG. 2 is a block diagram of a video camera equipped with an automatic focus adjustment device according to the present invention. In the figure, 7 is a focusing lens for focusing, and 8 is a moving lens for moving the focusing lens 7 in the optical axis direction. 9 is a drive circuit that drives the focus motor 8; 10 is a zoom lens for changing the magnification of the subject image; 11 is a zoom motor that rotates a zoom ring (not shown) to move the zoom lens lO; 12 1 is a drive circuit for the zoom motor 11, ls is a position sensor that detects the position of the zoom lens 10, and 14 is a master lens that forms a subject image on the image sensor 15. The subject light flux is guided to the focus detection optical system by an eight-point mirror 16, and then passes through an AF lens 17 and a microlens 18.
An image is formed on the CCD 19 by. Another 20 are CCD
21 is an A/D converter that converts the analog output from the CCD 19 into a digital value; 22 is an interface between the CCD driver 20 and the A/D converter 21 and a microcomputer 23; .

The microcomputer 23 uses the above-mentioned HF logic to determine the amount of deviation S, and calculates the amount of defocus from this amount of deviation S. By comparing this defocus amount with a preset focusing range, it is determined whether the object is in front focus, in focus, or in back focus. When the front focus is on, a signal is output from the microcomputer 23 to the drive circuit 9, and the focus motor 8 is driven for a time corresponding to the previously calculated defocus amount, so that the focusing lens 7 is moved in the focusing direction. On the other hand, when the rear focus is on, a signal is output from the microcomputer 23 to the drive circuit 9, and the first focusing lens 7 is moved in the extending direction.

Next, the operation of the automatic focus adjustment device using XII will be explained using the flowchart shown in FIG.

First, the CCD driver 2 is activated by a command from the microcomputer 23.
0 is driven, charge accumulation in the CCD 19 starts (F-1), and the output signal from the CCD 19 is converted into a digital value by the A/Df converter 21 and input to the microcomputer 23 (F-2). ). The microcomputer 23 uses the above-mentioned HF logic to find the deviation S, and calculates the defocus from this deviation ls (F-3). At this time, if vk>0. There are several places where vk, □〈o, and the difference D between the values of vk and vk, I is
e is a predetermined value (e.g. 256)
If it is larger, it is determined that there are several points that can be determined as one focal point. If there are several points that can be determined as in-focus points like this, there is a possibility that unnatural movements such as hunting may occur, so it is necessary to use this as an indicator and perform special processing. Then, it is determined whether there are two or more De 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, Stop the focus motor 8 (
F-5). Step (
Focus motor 8 based on the calculated value obtained in F-3)
to move the focusing lens 7 to the focusing position (F
-6), then proceed to the next stage of the flow. In short, in this embodiment, if two or more De values greater than a predetermined value are detected, the focus motor 8 is stopped, and when De becomes one, the focus motor 8 is driven again to move the focusing lens 7. be.

By doing the above, the focus motor 8 is stopped when there are two or more De values equal to or greater than a predetermined value, and the hunting phenomenon does not occur even in the case of a subject having a repetitive pattern.

FIG. 4 is a flowchart showing the operation of the second embodiment in January.

In the embodiment shown in FIG. 3, if two or more De values greater than a predetermined value are detected, the focus motor 8 must be stopped immediately, or even in such a case, focus can be achieved by moving the focusing lens 7 several times. There may be cases where

Therefore, in this embodiment, when two or more De values greater than a predetermined value are detected, the focus motor 8 is driven a predetermined number of times (for example, five times) and then stopped.

Figure 4 shows the operation, and the steps in Figure 1 (F-1
) to (F-4) are the same as the embodiment shown in FIG.

However, if there are two or more De values greater than the predetermined value, check whether the motor stop flag is set (F-5).
, if it is not set, a flag is set (F-6), and if the flag is already set, then the count value of the motor stop counter is checked (F-7), and this counter sets the initial value to "
5" and every time the focus motor 8 operates,
If the count value of the counter is "0", the focus motor 8 is stopped (F-8), and if it is not rOJ, the counter is decremented (F-9), and the focus motor 8 is stepped ( It is driven according to the defocus amount obtained in F-3).

There is no need to stop the focus motor 8 if there are no more than a predetermined value or two or more, so reset the motor stop flag (F-11) and set the counter to the initial value "5" (F-12). Drive 8 (
F-10).

According to this embodiment, it is possible to reach the focused point while driving the motor several times.

Next, FIG. 5 shows a part of the flowchart of the third embodiment. Other parts are the same as in FIG. In this embodiment, when De is equal to or greater than a predetermined value and De is two or more, the motor stop flag is not immediately set, but the history of the calculated defocus amount and its direction is stored in the memory in the microcomputer 23. , the focus motor 8 is stopped according to the history. As mentioned above, the microcomputer 23 can determine the front pin and rear pin from the calculation result of the HS logic formula, or when the calculation value of the rear pin is output after the calculation value of the front pin is output, or vice versa, i.e. When information about the front pin and the rear pin is received, it can be determined that hunting is actually occurring.

There, the microcomputer 2 checks whether the front pin and rear pin information has been entered.
If it is set, set the motor stop flag (F-6), and if it is not set, step (F-13).
Step F-10) to drive the focus motor 8.

In the first embodiment (see FIG. 3), the focus motor 8 is stopped when two or more De of a predetermined ffi or more are detected, so the focus motor 8 is stopped even if hunting does not actually occur. However, according to the present embodiment, this does not occur and the focus motor 8 is stopped only after hunting actually occurs. Also, instead of stopping the focus motor 8 immediately, it is driven several times.
The effect of the second embodiment is also obtained that the hunting may subside and the in-focus position may be reached during that time.

However, when driving the focus motor 8, an overshoot may occur in which the motor 8 is driven beyond the calculated focus amount due to variations in the dimensions of the drive system. It is possible that the condition is met due to overshoot of the cigarette and the focus motor 8 stops. However, even if overshoot occurs, if it is close to the in-focus point, it will eventually stop at the in-focus position without causing any hunting.
ff 聚性 is large.

Therefore, in the fourth embodiment shown in Fig. 56, when front focus and rear focus information is entered (F-13), it is then necessary to judge whether the defocus amount is within a predetermined value near the focus. F
-14) If it is within the predetermined value, set the motor stop flag (F-6), or if it is within the predetermined value, it is considered that the in-focus position will be reached without causing hunting, so stop the motor 8 1: (F-
1O), in this case, the predetermined value near the focus is the sensor decomposition f
1. It is set according to the magnification of the AF optical system or the controllability of the motor. The other parts of the flowchart of this embodiment are the same as those shown in FIG.

In the embodiment described above, a video camera is taken as an example, but the present invention is not limited thereto, but can also be applied to a general still camera. Further, the focus detection method is not limited to the TCL method, but can also 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 multiple points that can be determined as in-focus points based on the calculated value of the first stage of calculation, and it is determined that there are multiple points. Since the driving of the focus motor is stopped by the stop means when the object is detected, even if the object includes a repetitive pattern, smooth AF operation can be performed without causing hunting.

[Brief explanation of the drawing]

Figure 1 shows the overall configuration 1'' of an automatic focus adjustment device according to the present invention.
A. Fig. 2 is a block diagram showing one embodiment of the automatic focus adjustment device according to the present invention, Fig. 3 is a flowchart showing the operation of the embodiment of Fig. 2, and Figs. 4 to 6 show other embodiments. Flowchart showing an example. FIG. 7 to FIG. 1O are diagrams explaining the principle of the TCL method. l...Photographing lens, 6.19...CCD, 14...
・Master lens, 15...imaging element

Claims (2)

[Claims] (1) It has a calculation means that forms two types of subject images on an image sensor and calculates the defocus amount and direction of the photographing lens based on the phase difference between the two types of image signals, and the calculation means In an automatic focus adjustment device that uses a focus motor to move a photographing lens to its in-focus position based on a calculated value, it is determined whether there are multiple points that can be determined as in-focus points based on the calculated value of the calculation means. An automatic focusing device comprising: a determining means for determining a focus point; and a stopping means for stopping driving of the focus motor when the determining means determines that there are a plurality of points that can be determined as a focused point. (2) The automatic focus adjustment device according to claim 1, wherein the stopping means stops driving the focus motor in a manner according to the calculated value of the calculating means or its history.