JPH0553044A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To shorten the time of out-of-focus, while suppressing the power consumption of a focus motor, in a video camera, etc. CONSTITUTION:The device is constituted so that a timer counter device 12 for detecting whether a prescribed time elapses or not is connected to a focus evaluation value detecting means 7 for detecting a focus evaluation value 8, and when it is detected that the focus evaluation value 8 is zero in all movable areas of a focus lens 1, the focus lens 1 is moved to a stop position set in advance, and thereafter, whenever an overflow signal 17 is outputted from a timer counter device 12, the focus lens 1 is driven, and also, from the point of time when the focus evaluation value 8 in the movable area comes not to be zero, the lens driving control is restored.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applied to a video camera or the like, and relates to an automatic focus adjusting device adapted to perform automatic focus adjustment based on a video signal obtained from an image pickup device.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram showing the structure of a conventional automatic focus adjusting device. In FIG. 3, reference numeral 1 denotes a focus adjusting lens unit (hereinafter referred to as a focus lens), which is not shown in the figure. Is imaged on the image sensor 2 such as a CCD. A video signal processing circuit 3 is connected to the output side of the image sensor 2 and has a luminance signal (hereinafter referred to as Y signal) 4
Is output.

Reference numeral 5 is a high-pass filter (hereinafter referred to as HPF), to which the Y signal 4 output from the video signal processing circuit 3 is input. Reference numeral 6 denotes an integrating circuit, and the integrating circuit 6 and the HPF 5 constitute a focus evaluation value detecting means 10 to obtain a focus evaluation value 8. Reference numeral 7 denotes a lens drive control means which receives the focus evaluation value 8 and constantly monitors it. Reference numeral 9 is a focus motor, 11 is a focus encoder, and based on the position signal 19 of the focus lens 1 obtained by the focus encoder 11, the focus lens 1 is moved through the focus motor 9 so that the focus evaluation value 8 is maximized. Drive control.

Next, the operation of the above configuration will be described. The focus lens position signal 19 obtained by the focus encoder 11 is input to the lens drive control means 7, and the focus motor 9 is set so that the focus evaluation value 8 output from the integrating circuit 6 of the focus evaluation value detection means 10 becomes maximum. The position of the focus lens 1 is drive-controlled via this. At this time, if it is confirmed that the focus evaluation value 8 outputs zero in the entire movable range of the focus lens 1, the focus lens 1 is stopped at that position, and thereafter,
When it is detected that the focus evaluation value 8 is not zero, the automatic focus adjustment operation as described above is restarted.

[0005]

Since the conventional automatic focus adjustment device is constructed as described above, the focus evaluation value 8 is set while the focus lens 1 is stopped during the focus adjustment.
Since it is determined whether is not zero, the focus evaluation value 8 remains zero when the stop position is away from the in-focus position of the subject by the depth of focus or more even if the subject changes. Therefore, the lens drive control based on the focus detection is not restarted, and as a result, there is a problem that the focus shift occurs.

The depth of focus (d) is expressed by the following equation using the F value (F) of the lens and the circle of confusion (δ). d = Fδ ……………… (1)

The present invention has been made to solve the above problems, and an object of the present invention is to provide an automatic focusing apparatus capable of preventing focus deviation while suppressing power consumption of a focus motor. I am trying.

[0008]

An automatic focus adjusting device according to the present invention is obtained from a zoom lens having a zooming effect, a focus adjusting lens unit for focusing an object, an image pickup device, and this image pickup device. A focus evaluation value detecting means for detecting a level of a predetermined frequency component of a video signal as a focus evaluation value in a constant cycle, and a change in the detected focus evaluation value is monitored, and the focus adjusting lens unit is placed on the optical axis of the lens. A lens driving means for moving the focus along the axis to adjust the focus; a lens position detecting means for detecting the position of the focus adjusting lens portion; a focal length detecting means for detecting the focal length of the zoom lens; Stores a movable area and a stop position set in advance corresponding to the indication value of the detection means,
The lens drive means comprises: a lens drive control means for stopping and controlling the drive of the focus adjusting lens part which is moved by the lens drive means; and a timer counter device for detecting whether or not a predetermined time has elapsed, the lens drive means comprising: Only when the focus evaluation value detected by the focus evaluation value detection means cannot detect the in-focus position in the entire movable region of the focus adjustment lens unit, the focus adjustment lens unit is detected every time the timer counter device detects a fixed time. The lens drive control based on the focus evaluation value detecting means is restored from the time when the focus evaluation value is not zero and it is detected that the focus evaluation value is not zero.

It is preferable that the stop position of the focus adjusting lens portion by the lens driving means is set between the infinity position and the close-up position determined according to the focal length of the zoom lens.

In the movable area of the focus adjusting lens section, the depth of focus is added to or subtracted from the focus position at infinity and the focus position at the closest end of the focus adjusting lens section. It is preferable to set the positions obtained by the above as both ends.

Further, the focal length of the zoom lens designated by the zoom encoder is divided into a plurality of continuous regions, and the movable region and the stop position of the focus adjusting lens unit are divided into the divided regions of the zoom lens. It is preferable to set only one representative for each focal length.

[0012]

According to the present invention, when the lens drive control means executes the automatic focus adjustment operation based on the output of the focus evaluation value detection means, if the focus evaluation value outputs zero in the entire movement area of the focus lens. For example, the focus lens is driven and moved to a stop position set by the focal length of the zoom lens and the unique shooting close distance to stop. Next, the timer counter device is cleared, and then each time the timer counter device overflows, the focus lens is driven to detect that the focus evaluation value in the movable area is not zero, and the focus is restarted from the point when it is no longer zero. By resuming the lens drive control based on the evaluation value detection means, it is possible to prevent focus deviation.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the structure of an automatic focusing apparatus according to an embodiment of the present invention. In FIG.
11 to 19 are the same as those of the conventional example shown in FIG. 3, corresponding parts are designated by the same reference numerals, and detailed description thereof will be omitted.

In FIG. 1, a zoom lens 14 is arranged in front of the focus lens 1. A zoom encoder 13 has a focal length 18 of the zoom lens 14.
Is input to the lens driving means 7. A zoom motor 12 drives and controls the zoom lens 14. 12
Is a timer counter device, which inputs the clear signal 16 and thereafter drives the focus lens 1 to stop each time the overflow signal 17 is returned to the lens driving means 7 at regular intervals. The lens drive control means 7 always monitors the focus evaluation value 8, and in advance, for example, the relationship table and the stop position of the movable range set by the zoom lens 14 and the focal length range divided into 32 are, for example, It is stored using a ROM.

Next, the operation of the above configuration will be described. In the automatic focusing operation, the lens drive control means 7
In addition to the focus evaluation value 8 output from the integrating circuit 6 of the focus evaluation value detecting means 10, a focus lens position signal 19 obtained by the focus encoder 11 and a focal length signal of the zoom lens 14 obtained by the zoom encoder 13 18 are input respectively, and the lens drive control means 7 constantly monitors the focus evaluation value 8.
The focal length range and the zoom lens 14 divided into 32 in advance
The relational table of the movable area and the stop position set by are stored. Here, if the focus evaluation value 8 is zero in the entire movable area of the focus lens 1, the zoom lens 14 obtained by the zoom lens encoder 13
The focus lens 1 is driven and stopped at the stop position set by the focal length signal 18 and the photographing close distance peculiar to the lens barrel.

Next, the clear signal 16 is input to the timer counter device 12, and thereafter, each time the timer counter device 12 returns the overflow signal 17, the focus lens 1 is returned.
Is driven to detect whether or not the focus evaluation value 8 in the movable area is zero, and if it is not zero, the automatic focus adjustment operation based on the focus evaluation value detecting means 10 is restored from that point, and If only zero is detected even if all the movable areas are driven, the focus lens 1 is moved to the stop position.
After stopping, the focus is automatically adjusted by repeating the above operation.

FIG. 2 is an explanatory view showing an example of setting the movable area of the focus lens 1. In FIG. 2, a broken line A is the closest object distance, and a solid line B is the infinite object distance. In each case, a curve and a shaded portion showing the relationship between the focal length f and the movement amount FCV of the focus lens 1 are the movable areas in which the curves are set.

A method of setting the stop position and the movable area of the focus lens in the above embodiment will be described as follows. The focal length f of the zoom lens 14 is changed from fW to fT (fW> fT), and this focal length range is divided into 32 parts. Each focal length range is fI-1 to fI
(I = 1 to 32, f0 = fw, f32 = ft). As for the stop position for each of these focal length ranges, the focus lens stop position is FC, and the maximum value of the focus lens position at the shortest distance in each focal length range is MA.
Letting X (FC near) and the minimum value of the focus lens position at infinity be MIN (FC INF), FC = {MAX (FC near) + MIN (FC INF)} / 2 (2) Is set. In addition, with respect to each movable range, the moving amount FCV indicating the movable range of the focus lens with respect to each of the focal length ranges is expressed by the following equation, where d is the depth of focus. FCV (+) = MAX (FC near) -d-FC ... (3) FCV (-) = FC- {MIN (FC INF) + d} ... (4)

In the above embodiment, the ROM is used. However, even if a microcomputer is provided, the same effect as that of the above embodiment can be obtained.

[0020]

As described above, according to the present invention, the timer counter device is used to focus on the preset stop position when the focus evaluation value outputs zero in the entire movable range of the focus lens. Since the lens is moved and then driven every time the timer counter device overflows, the power consumption by the lens drive control means can be suppressed. In addition, since the lens drive control based on the focus evaluation value detection means is restored from the time when the focus evaluation value in the movable area is not zero, the focus deviation time can be shortened.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an automatic focus adjusting device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a relationship between a movable area of a focus lens and a stop position according to an embodiment of the present invention.

FIG. 3 is a block diagram showing a configuration of a conventional automatic focus adjustment device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 focus lens 2 image sensor 7 lens drive control means 8 focus evaluation value 10 focus evaluation value detection means 11 focus encoder 12 timer counter device 13 zoom encoder 14 zoom lens 15 zoom motor 18 focal length signal 19 focus lens position signal

Claims (4)

[Claims] 1. A zoom lens having a zooming function, a focus adjusting lens section for focusing an object, an image sensor, and a focus of a level of a predetermined frequency component of a video signal obtained from the image sensor at a constant cycle. Focus evaluation value detection means for detecting as an evaluation value, and lens drive means for monitoring the change in the detected focus evaluation value and moving the focus adjustment lens portion along the optical axis of the lens to perform focus adjustment. A lens position detecting means for detecting the position of the focus adjusting lens portion, a focal length detecting means for detecting the focal length of the zoom lens, and a movement set in advance corresponding to an instruction value of the focal length detecting means. Memorizable area and stop position,
The lens drive means comprises: a lens drive control means for stopping and controlling the drive of the focus adjusting lens part which is moved by the lens drive means; and a timer counter device for detecting whether or not a predetermined time has elapsed, the lens drive means comprising: Only when the focus evaluation value detected by the focus evaluation value detection means cannot detect the in-focus position in the entire movable region of the focus adjustment lens unit, the focus adjustment lens unit is detected every time the timer counter device detects a fixed time. The automatic focus adjustment device is configured so that the lens drive control based on the focus evaluation value detection means is restored from the time when the focus evaluation value is not zero and is detected. 2. The stop position of the lens unit for focus adjustment by the lens driving means is set between the infinity position and a close-up position determined according to the focal length of the zoom lens. Automatic focus adjustment device. 3. The movable area of the focus adjustment lens unit is configured such that the depths of focus are added to or subtracted from the focus position at infinity and the focus position at the closest end of the focus adjustment lens unit, respectively. The automatic focus adjusting device according to claim 1, wherein the positions obtained by the above are set as both ends. 4. The focal length of the zoom lens, which is designated by the zoom encoder, is divided into a plurality of continuous regions, and the movable region and the stop position of the focus adjustment lens unit are the respective focal points of the zoom lens. 4. The automatic focus adjusting device according to claim 1, wherein only one is typically set for each distance.