JPS61267463A - Auto-focusing device - Google Patents

Abstract

PURPOSE:To perform the focusing operation which has a high accuracy and is superior in operability, by providing contrast value selecting means which extracts high frequency components of a video signal as contrast values corresponding to two focus detection ranges different from each other at least and selects optimum one of them as the contrast value of an object. CONSTITUTION:The first contrast value corresponds to the narrower focus detection range, and the second contrast value corresponds to the wider focus detection range. The first contrast value is inputted to one terminal of a comparator 18 and is compared with a contrast decision value which is set preliminarily and is inputted to the other terminal, and the comparator 18 is inverted to generate an output signal if the first contrast value is larger, but the output is not generated from the comparator 18 if the first contrast value is smaller. A switch 19 is switched in accordance with the presence/absence of the output of the comparator 18, and the first contrast value is transmitted to a motor control part 20 in case of the presence of the output, but the second contrast value is transmitted to the motor control part 20 as the focus detection contrast value in case of the absence of the output.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an autofocus device for a video camera;
In particular, the present invention relates to an autofocus device that controls a focus detection range and performs highly accurate focus adjustment.

Conventional technology Conventional autofocus devices in video cameras use a contrast detection method using TTL photometry, but the focus detection range on the shooting screen is generally fixed to a fixed size at a fixed position, and focus detection accuracy is limited. Since the focus detection range is poor, there is a device proposed in Japanese Patent Application Laid-open No. 58-219505 that proposes varying the focus detection range.

This publication allows the focus detection range to be changed automatically or manually in accordance with the focal length of the zoom lens.

Problems to be Solved by the Invention In the conventional device described above, even if the focus detection range can be changed according to the focal length of the zoom lens, there is only one type of focus detection range at the same focal length, and the distance If two or more different subjects exist within the focus detection range, the focus will be on a subject that was not intended by the photographer, or if there is no contrast within the focus detection range and there is strong contrast between the subjects outside the focus detection range, focus detection will not be performed. The camera may become unable to focus, causing malfunctions such as repeatedly focusing and out of focus, and even if you manually switch the focus detection range, it is cumbersome to confirm the subject and switch. It has the following problems.

The present invention provides an autofocus device using contrast detection that eliminates such problems.

Means for Solving the Problems In order to solve the above problems, the autofocus device of the present invention extracts the high frequency components of the video signal as contrast values corresponding to at least two different focus detection ranges, and , comprising contrast value selection means for selecting the optimum contrast value of the object.

``By operating the motor control circuit and motor to drive the lens at the contrast value in the optimal focus detection range according to the subject situation selected by the working contrast value selection means, precise focusing operation is possible.

Embodiment FIG. 1 is a configuration diagram of an autofocus device according to an embodiment of the present invention, FIG. 2 is an operational waveform diagram of the autofocus device according to FIG. 1, and FIGS. 3 and 4 are autofocus devices of the present invention. FIG. 3 is a diagram showing the relationship between a subject image and a focus detection range by the device. In Fig. 1, 1 is a motor that drives the lens, 2 is a lens, 3 is a camera circuit, and 4 converts the subject light incident on the lens into an electrical signal, and extracts the high frequency component of the video signal output from the camera circuit 3. bipulse filter,
Reference numeral 6 denotes a contrast value selection means that extracts high frequency components of the video signal as contrast values corresponding to different focus detection ranges, and selects the optimum contrast value among the contrast values as the contrast value of the subject. Further, the contrast value selection means 6 includes a pulse signal generator 6 which generates wide pulses and narrow pulses corresponding to wide and small focus detection ranges according to horizontal and vertical synchronizing signals from the camera circuit 3; a gate 11 that allows the high frequency component signal of the bipulse filter 4 to pass through for a time corresponding to the pulse widths of the wide pulse and narrow pulse generated from the generator 6;
Gate 1 for the duration of the narrow pulse and wide pulse.
A contrast value generation unit 1 holds the peak value of each high frequency signal that has passed through the contrast value as a contrast value.
4, and a contrast value selection section 17 that selects one of the two contrast values generated from the contrast value generation section 14. Further, 2o is a motor control circuit unit that detects the output contrast value from the contrast value selection means 6 in synchronization with the vertical signal in the pulse signal generation unit e and in synchronization with the generated wide pulse, and controls the rotation of the motor 1. be.

The operation of the autofocus device of the present invention having the above configuration will be explained with reference to the operational waveform diagram in FIG.

A horizontal synchronizing signal as shown in FIG. 2a is output from the terminal 3-1 of the camera circuit 3, and a vertical synchronizing signal as shown in b is output from the terminal 3-2. 6, a narrow width C pulse is applied from the first pulse signal generation circuit 7, a wide width d pulse signal is applied from the second pulse signal generation circuit 8, and a pulse signal of width d is applied to the third pulse signal generation circuit 9.
, the pulse signal e is sent to the fourth pulse signal generation circuit 1.
From 0 to f pulse signals are generated, respectively.

Then, the pulse signals C and e are input to the AND circuit 21, which generates the pulse signal q, and the pulse signals d and f are input to the AND circuit 22 and output from the AND circuit 21.
A pulse signal is generated from the circuit 22.
By making the pulse width of l'I correspond to the vertical and horizontal widths of the narrow and wide focus detection ranges, the pulse signals of q and h can be made to correspond to the narrow focus detection range of the screen. It is compatible with a wide range of areas.

On the other hand, the video signal of the camera circuit 3 is filtered through a bi-pulse filter 4.
A high frequency component signal is extracted by and generates a signal such as i, this signal i is applied to the gate 11, and the high frequency signal 1 is output from the first gate 12 which passes the signal for a narrow width time of the pulse signal q. , and a high frequency signal of k is output from the second gate 13 which allows the signal to pass only during a wide period of time of the pulse signal.

These signals j and ni are applied to the contrast value generating section 14, and the signal j is held in the first peak hold circuit 16, where the peak value of the signal is held as the first contrast value.

This first contrast value is the one that has passed through the narrow gate q and is, so to speak, in the narrow focus detection range, while the second contrast value is the peak of the signal that has passed through the wide gate h. The value is obtained by being held by the second peak hold circuit 16, and is in the wider focus detection range. Then, the first contrast value is input to one end of the comparator 18, and it is compared to see whether the first contrast value is larger or smaller than a contrast judgment value set in advance and input to the other end. If it is large, comparator 18 inverts and produces an output signal, while if it is small, comparator 1
There is no output from 8.

The switch 19 is switched depending on whether there is an output from the comparator 18, and when there is an output from the comparator 18, the switch 19 is in the state shown and transmits the first contrast value to the motor control unit 2o, and there is no output from the comparator 18. At times, the switch 19 is switched as shown to transmit the second contrast value to the motor control unit 2o as the focus-detected contrast value.

Note that the determination value inputted to one end of the comparator 18 and compared with the first contrast value is set to a value slightly larger than the lowest value at which the motor control unit 20 can determine an increase or decrease in contrast.

In addition, the first contrast value was compared using a comparator, but conversely, the second contrast value is compared using a comparator, and depending on whether or not the output is output, a switch is changed to select either the first or second contrast value. It may also be used as a contrast value for focus detection.

The motor control unit 20 detects the first or second contrast value input to the motor control unit 20 in synchronization with the pulse signal generated by the fourth pulse signal generation circuit 10, and compares the detected contrast value with the previous value. By comparing and detecting an increase or decrease, the motor 1 is reversibly rotated to move the lens 2 closer to the peak of the contrast value, which is the focusing direction, and bring the lens into focus.

The operation is as described above, but when objects at different distances are present on the screen and there is contrast in a narrow detection range as shown in Fig. 3, the contrast value in the narrow focus detection range (a) is set by the contrast value selection unit 17. The first contrast value in the narrow detection range (a) is selected as the focus detection contrast of the subject because it is larger than the judgment value of the comparator 18, and the fourth contrast value, which has no contrast in the narrow detection range because the subject is relatively flat, is selected as the focus detection contrast of the subject. In the case of the figure, the narrow detection range (
The contrast value of (a) cannot exceed the judgment value of the comparator 18 of the contrast signal selection section 17, and the output of the comparator 18 is not inverted. ) is selected as the focus detection contrast of the subject, and focusing operations are performed based on the respective contrasts.

In this example, contrast values for two types of focus detection ranges, narrow and wide, were selected, but the number of focus detection ranges was further increased to three or more, and the contrast was determined sequentially from the narrow detection range to the wide one. By selecting the contrast value, it is also possible to perform focusing with higher precision.

Effects of the Invention As described above, the autofocus device of the present invention automatically selects the contrast value in the focus detection range according to the situation of the subject and uses it as the contrast value of the subject, so it is highly accurate and easy to operate. Excellent focusing operation is possible.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of an autofocus device according to an embodiment of the present invention, Fig. 2 is an operational waveform diagram of the autofocus device according to Fig. 1, and Figs. FIG. 3 is a related diagram of focus detection ranges. 1...Motor, 2...Lens, 3...
... Camera circuit, 4 ... Bipulse filter, 5 ... Contrast value selection means, 20 ...
...Motor control circuit section. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 3
Figure 2~! Scary q) 1d

Claims (1)

[Claims] The camera circuit converts the subject light incident through a lens driven by a motor whose operation is controlled by a motor control circuit into an electrical signal, and focuses the lens based on the high frequency component signal extracted from the output video signal. An autofocus device for a video camera that extracts two contrast values having at least different values corresponding to at least two different focus detection ranges from a high frequency component signal extracted from the video signal, and An autofocus device comprising contrast value selection means for selecting one of the contrast values as the optimum contrast value for a subject on a photographing screen and applying the selected contrast value to the motor control circuit.