JPH0446471A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To correct the change of a high frequency component in a video signal by means of zooming by changing the window area of a window generated from a window generating means and the cut-off frequency of a filter based on the focal length information of a zoom lens detected by a detecting means by a high frequency component correcting means. CONSTITUTION:When a zoom lens 2 is fixed, the optical image of an object picked-up by a focus lens 1 is video-signalized by a photoelectric converter 3. The high frequency component of this video signal is extracted by a filter 4, and outputted in an integrator 6 through a detector 8 and a switch SW. A focus evaluation value as the integrated result of the integrator 6 is inputted in a focusing control part 7, and the focusing control part 7 focuses by driving the focusing mechanism of the focus lens 1 as the above mentioned focus evaluation value is maximized. At this time, a focal length sensor 10 detects the focal length information corresponding to the magnification of the zoom lens 2, and outputs this in the focusing control part 7.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an automatic focusing device for automatically focusing a lens of a video camera or the like.

(Prior Art) A conventional automatic focus adjustment device of this type has a configuration as shown in FIG. That is, the optical image formed on the photoelectric converter 3 via the focus lens 1 and the zoom lens 2 is
Here, it is photoelectrically converted into a video signal, and this video signal is input to the filter 4. The filter 4 extracts high frequency components from the input video signal and outputs them to the detector 8.

The detector 8 detects the input high frequency component and outputs the output signal to the integrator 6 via the switch SW. here,
The window generator 5 generates a window that is co-centered with the screen and has an area smaller than the screen by turning on and off a switch SW. Therefore, during the period corresponding to the window of the video signal, the switch SW
is turned on, and the detection signal of the detector 8 is transmitted to this switch S.
It is input to the integrator 6 via W. The integrator 6 integrates the detection output and outputs a focus evaluation value, which is the integration result, to the focus adjustment control section 7. The focus adjustment control unit 7 moves the focus adjustment mechanism of the focus lens so that the focus evaluation value inputted from the integrator 6 is maximized.
Performs focus control.

By the way, during the period when the focus is adjusted as described above,
Alternatively, if the zoom switch 9 is pressed while the focus adjustment is completed, the zoom lens 2 moves and the image outline of the subject changes. Since the size of the image frame changes during such zooming, the focus evaluation value, which is the output of the integrator 6, changes as shown in FIG. 7 even when the subject is stationary.

As a result, the focus adjustment control unit 7 determines that the subject has moved and operates the focus adjustment mechanism of the focus lens 1. For this reason, when zooming is performed using the zoom lens 2, there is a drawback that focus adjustment control is performed incorrectly due to changes in the image contour.

(Problem to be Solved by the Invention) In a conventional automatic focusing device that extracts high-frequency components of a video signal and operates the automatic focusing mechanism of the focusing lens 1 so that the integrated value of the high-frequency components is maximized, the zoom lens This has the disadvantage that when zooming a subject, it is impossible to distinguish between changes in the image outline and movement of the subject, resulting in incorrect autofocus operation.

SUMMARY OF THE INVENTION Therefore, the present invention aims to eliminate the above-mentioned drawbacks, and aims to provide an automatic focus adjustment device that can maintain a focused state even during zooming when the subject is stationary. .

[Structure of the invention]

(Means for solving the problem) The present invention includes a zoom lens after a focus lens,
In addition, a high frequency component is extracted through a filter from a portion of the video signal obtained by photoelectrically converting the optical image formed by the focus lens, which is divided by a window provided separately, and the integrated value of this high frequency component is maximized. In an automatic focus adjustment device that adjusts the focus of the focus lens so that 1
window generating means for generating a window of an arbitrary area smaller than a screen; and a detecting means for detecting the focal length of the zoom lens; and a detecting means for detecting the focal length of the zoom lens. The present invention includes a high-frequency component correction means for changing the window area of the window and the cut-off frequency of the filter, and the number of the filters, and is configured to correct changes in the high-frequency components in the video signal due to zooming.

(Function) In the automatic focus adjustment device of the present invention, the window generating means generates a window having an arbitrary area of one screen or less.

The detection means detects the focal length of the zoom lens.

The high-frequency component correction means changes the window area of the window generated from the window generation means and the cutoff frequency of the filter based on the focal length information of the zoom lens detected by the detection means, thereby changing the image signal by zooming. The change in the high frequency component of is corrected.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings, in which the same parts as those of the conventional example are denoted by the same reference numerals. FIG. 1 is a block diagram showing an embodiment of an automatic focus adjustment device of the present invention.

1 is a focus lens that forms an optical image of a subject on a photoelectric converter 3, and 2 is a zoom lens that changes the magnification of the optical image.

3 is a photoelectric converter that converts an optical image into a video signal; 4 is a filter that extracts high frequency components from the video signal; 5 is a window generator that generates a window of arbitrary area using a switch SW; 6 is a high frequency component. an integrator that integrates the component detection signal; 7 is a focus adjustment control unit that adjusts the focal length of the focus lens;
8 is a detector for detecting the high frequency component signal from the filter 4;
9 is a zoom switch that changes the magnification of zoom lens 2, 1
0 is a focal length sensor that detects the focal length of the zoom lens 2.

Here, the window generator 5 and switch SW constitute a window generating means, the focal length sensor 10 constitutes a detecting means, and the focus adjustment control section 7 constitutes a window area changing means, a filter characteristic changing means, a calculating means, and a controlling means. There is.

Next, the operation of this embodiment will be explained. zoom lens 2
When the focus lens 1 is fixed, the optical image of the subject captured by the focus lens 1 is converted into a video signal by the photoelectric converter 4. High frequency components of this video signal are extracted by a filter 4 and output to an integrator 6 via a detector 8 and a switch SW. The focus evaluation value, which is the integration result of the integrator 6, is input to the focus adjustment control section 7, and the focus adjustment control section 7 drives the focus adjustment mechanism of the focus lens 1 so that the focus evaluation value becomes the maximum, thereby focusing. let

When the zoom switch 9 is pressed in this state,
The magnification of zoom lens 2 changes and focus lens 1
The image contour of the optical image formed by this changes. At this time,
The focal length sensor 10 detects focal length information corresponding to the magnification of the zoom lens 2 and outputs this to the focus adjustment control section 7. The focus adjustment control unit 7 controls the input zoom lens 3.
Control is performed to change the window area of the window generating section 5 based on the focal length information.

Here, the window area is determined from the characteristic diagram shown in FIG. 2, which shows the relationship between the focal length information and the window area. That is, f in the focal path Mf of the zoom lens 2.

≦f i<fn+1, fn+1/f, =A1/
Assuming that there is a relationship such that A The images have similar shapes as shown in FIG.

Also, when the focal length of the zoom lens 2 changes, the first
A focus adjustment control section 7 shown in the figure performs control to change the cutoff frequency of the filter 4. However, it is assumed that the transfer function of the filter 4 can change.

FIG. 4 shows the relationship between the cutoff frequency of the filter 4 and the window area. If the low and high cutoff frequencies of the filter 4 when the window area is A□ are W4 and wH, respectively, then the focus adjustment control section 7 are the low and high cutoff frequencies of the filter 4 when the window area is A.
Change to Ao. By this frequency change, the change in spatial frequency due to the change in image contour due to zooming of the zoom lens 2 is corrected so as to be constant.

Further, the focus adjustment control section 7 divides the focus evaluation value given from the integrator 6 by the window area of the window generation section 5, and uses the result as a new focus evaluation value. As a result, when the subject is stationary, the relationship between the focal length of the zoom lens 2 and the focus evaluation value becomes as shown in FIG. 5, where f is f. That's all f. +1
The focus evaluation value remains constant during the period below. If the focus evaluation value is constant, the focus adjustment control unit 7 does not adjust the focus of the focus lens 2, so that the focused state is maintained. Furthermore, f
o and f. , the focus evaluation value changes at the break of the first class stairs, but the control of the focus adjustment control unit 7 is performed at each staircase,
Changes due to this break are ignored.

According to this embodiment, when the object is zoomed with the zoom lens 2, if the value obtained by dividing the focus evaluation value of the integrator 6 by the window area becomes constant during a certain period as shown in FIG. is determined to be stationary, and the focus adjustment control unit 7 maintains the current state and does not perform the focus adjustment operation of the focus lens 2, so that the in-focus state can be maintained even when zooming a stationary subject. .

〔Effect of the invention〕

As described above, according to the automatic focus adjustment device of the present invention,
If the subject remains still during zooming, it is possible to maintain focus.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the automatic focusing device of the present invention, FIG. 2 is a diagram showing an example of changes in window size with respect to the frame size in FIG. 1, and FIG. 3 is a diagram showing focal length and window size. Figure 4 shows the relationship between window area and cut-off frequency of the filter. Figure 5 shows the relationship between the focal length and focus evaluation value of the device shown in Figure 1. FIG. 6 is a block diagram showing an example of a conventional automatic focus adjustment device, and FIG. 7 is a diagram showing the relationship between focal length and focus evaluation value in the conventional device. 1...Focus lens 2...Zoom lens 3...Photoelectric converter 4...Filter 5...Window generator 6...Integrator Hiroshi, 1liij kan 7...Focus adjustment control unit 8 ...Detector 9...Zoom switch

Claims (1)

[Claims] A zoom lens is provided after the focus lens, and a video signal obtained by photoelectrically converting the optical image formed by the focus lens is extracted from a portion partitioned by a separately provided window through a filter, and high-frequency components are extracted. An automatic focus adjustment device that adjusts the focus of the focus lens so that the integrated value of the high-frequency component is maximized, comprising: window generation means that generates a window with an arbitrary area of one screen or less; and a focal length of the zoom lens. and a high-frequency component correction means for changing the window area of the window generated by the window generation means and the cutoff frequency of the filter based on the focal length information of the zoom lens detected by the detection means. An automatic focus adjustment device comprising: an automatic focus adjustment device that corrects a change in the high frequency component in a video signal due to zooming.