JPS6231813A - Automatic focus adjusting device - Google Patents

Abstract

PURPOSE:To absorb the frequency component change of the video signal and to change over smoothly the high accurate focus and the focus lens driving speed by selecting the optimum BPF by the information of both detecting means of the zoom position and the diaphragm position. CONSTITUTION:The output of a diaphragm position and zoom lens position detecting circuits 22 and 24 enters respectively a diaphragm position detecting means 29 and a zoom position detecting means 28 as the information of three bits through A/D conversion devices 26 and 25. By the information of the means 28 and 29, the assembling of the optimum BPF is selected and switches 31 and 32 are changed over. Thus, the optimum BPF is selected, the frequency component change of the video signal is absorbed, the focus accuracy is maintained regardless of the zoom position and the diaphragm position of the photographing lens, and the driving speed of the focus lens can be changed over smoothly.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an automatic focusing device for a video camera.

One of the automatic focusing devices applied to conventional technology video cameras is
There is a method (hereinafter abbreviated as TTL focusing method) in which an object image passing through an imaging lens is optically modulated at a constant cycle, a focal direction is determined from the modulation signal, and the imaging lens is driven to an appropriate focusing position.

To explain this principle below, first, FIG. 4 shows the relationship between the output of a video signal that has passed through a band pass filter (hereinafter abbreviated as BPF) and the focus lens position. Modulating the optical path of the subject image at a constant cycle corresponds to slightly changing the focus lens position. When the optical path is modulated with a waveform of X at point A, the output of the BPF becomes X. At point B near the focused point, even if the optical path is modulated at the same level as χ, the output will be ``, and the signal level will be small.If the optical path is modulated at point 0 beyond the focused point, the output of the barb will be obtained, but the phase will be relative to X. From the above, the output signals of the BPF have a phase difference of 180° before and after the in-focus point.

The output signal becomes smaller as it approaches the focal point and becomes zero at the focal point. Using this principle, the optical path modulation signal and B
The direction of the focusing position is determined by comparing the phases of the output signals of the PF, and the amplitude level of the output signals determines the direction of the focusing position.
The driving speed of the focus lens can be controlled. FIG. 5 shows the basic configuration of a TTL focusing system based on the above principle. ] is an imaging lens housing, 2 is a focus lens, 3 is an optical path modulator, 4 is an imaging device, 5 is a mid-range BPF, 6 is a high-range BPF 17, and 8 is a modulation level detection circuit, which detects the image signal by optical path modulation. Detecting changes. 9 is a signal level detection circuit. In order to achieve focus accuracy here, it is necessary to use a BPF (high-frequency BPF) whose band is set to a high frequency, but an output signal cannot be obtained when the subject image is largely blurred. Therefore, in addition to the high-frequency BPF 6, we use a BPF (mid-range BPF) 5 whose band is set to a low frequency, and when the subject is largely blurred, the output signal of the mid-range BPF 5 moves the focus lens in the focusing direction. Drive, high range BP
By switching to the high-frequency BPF 6 output signal at the stage when the F 6 output signal is obtained, focusing accuracy can be improved. Figure 4 shows high range BPF 6 and mid range BPF 5.
shows the output signal characteristics with respect to the focus lens position.

Therefore, in the signal level comparison circuit 10, when the output level of the signal level detection circuit 9 exceeds VB, the mid-range BPF 5
The switch 11 is switched from the output by the high frequency BPF'6 to the output by the high frequency BPF'6. Reference numeral 12 denotes a synchronous detection circuit, which synchronously detects the output signal optically modulated by the output of the optical path modulation oscillator 13, determines the driving direction of the focus lens 2, and transmits the result to the focus lens driving circuit 4.

On the other hand, the speed of the focus lens is changed by the switch 17 based on the output of the signal level comparison circuit 10. In a state where the drive direction of the focus lens is determined by the output of the mid-range BPF 5 (hereinafter referred to as mid-range operation), the output of the constant voltage circuit 18 is transmitted to the focus lens drive circuit 14, but the output of the high-range BPF 6 is not used. This is abbreviated as high-frequency operation below the soft type that determines the driving direction of the focus lens. ), the optical path modulated output signal is rectified by the double-wave rectifier circuits 1.9 and 20, and is sent to the focus lens drive circuit 14 through the NAM circuit 15 which outputs the higher level of the two input signals as the output signal. Reportedly. 16 is a drive circuit for the optical path modulator.

Problems to be Solved by the Invention FIG. 7 shows the optical path modulation output with respect to the focus lens position. Since the frequency component of the imaging signal changes depending on the zoom position of the imaging lens, the optical path modulation output of the same subject is a −
* Changes to b (Te1e side), a − + c (Wide side), and changes to ALC (Auto Light Co
Since the optical path modulation output changes depending on the aperture position (wtrol), there have been problems such as a decrease in the accuracy of the focusing position and a failure to smoothly connect the drive speeds of the focus lens. An object of the present invention is to eliminate the above-mentioned drawbacks, and to maintain focusing accuracy regardless of the zoom position or aperture position of the imaging lens, and to smoothly switch the drive speed of the focus lens.

Means for Solving the Problems In order to achieve the above object, the present invention detects the zoom position and the aperture position, inputs both information into a microcomputer, and selects the optimal BPF from among a plurality of BPFs.
It is designed so that you can select.

Function: This makes it possible to select the optimum drive speed for the focus lens and achieve highly accurate focusing.

EXAMPLE An example of the present invention will be described below based on the drawings. FIG. 1 is a block diagram of one embodiment of the present invention. In the figure,
Components that are the same as those in the conventional example shown in FIG. 5 are given the same reference numerals.

21 is an aperture, 22 is an aperture position detection circuit, 23 is a zoom lens, 24 is a zoom lens position detection circuit, 25.26 is an NΦ converter, 27 is a microcomputer, 28 is a zoom position detection means, and 29 is an aperture position detection means , 30 is BPF
The selection means selects the optimum BPF combination from a table based on the information from the zoom position detection means 28 and the aperture position detection means 29, and switches the switches 31 and 32.

33 and 34 are BPFs with different bands. BPF 3
3 is a band between BPF s and BPF 6, and semi-high band BPF and BPF 34 are bands higher than BPF 5 and will be abbreviated as super high band BPF hereinafter. In this configuration, the output of the zoom position detection circuit 24 is converted into a digital quantity by the ψ converter 25, and is input to the zoom position detection means 28 as 3-bit information. Similarly, the output of the aperture position detection circuit 22 passes through the A/D converter 26 and enters the aperture position detection means 29 as 3-bit information. Zoom position detection means 28
Then, divide Te1e-Wide into 0 to 7, and
The best position is set to 0. The aperture position detection means divides Fl,4 to Fl6 into 0 to 7, and calculates Fl,4 (
(open) position is set to 0. From both data, the second
Based on the table shown in the figure, the BPF selection means 30 operates the switches 31 and 32 to select the machine points A-F shown in the table.
Select the high-range BPF and the mid-range BPF. The frequency characteristics of the four BPFs 5, 6, 33, and 34 are as shown in Figure 3, and when the BPF output characteristics move from a to b in Figure 7 due to the aperture amount or zoom position, the frequency Switching to a BPF with a low frequency band, and when moving from a to C, switching to a BPF with a high frequency band to achieve highly accurate focusing and smooth focus lens drive speed.

Effects of the Invention As is clear from the above embodiments, the present invention selects the optimal BPF' by detecting the aperture position and zoom lens position, absorbs changes in the frequency components of the video signal, and achieves highly accurate focusing and smooth focusing. It is possible to realize an automatic focus adjustment device that enables a focus lens drive speed of

[Brief explanation of drawings]

FIG. 1 is a block diagram of a focus adjustment device in an embodiment of the present invention, and FIG. 2 is a diagram showing a table of BPF switching with respect to the zoom position and aperture position in the BPF selection means.
Fig. 3 is a characteristic diagram showing the frequency characteristics of BPF, Fig. 4 is a signal output characteristic diagram of BPF with respect to the focus lens position,
Figure 5 is a block diagram of a conventional T'l''L type focus adjustment device, and Figure 6 is a mid-range/high-range B with respect to the focus lens position.
FIG. 7 is a diagram showing the signal output characteristics of the BPF with respect to the focus lens position when the zoom lens position and the aperture position change.
DESCRIPTION OF SYMBOLS 11... Imaging lens housing, 2... Focus lens, 3... Optical path modulator, 4... Imaging device, 5... Mid-range BPF, 6... High-range BPF, 7
, 8... Modulation level detection circuit, 9... Signal level detection circuit, 10... Signal level comparison circuit, 11.17
...Switch, 12...Synchronous detection circuit, 13...
Oscillator, 14... Focus lens drive circuit, 15.
... NAM circuit, 16 ... Optical path modulator drive circuit, 18
...constant voltage circuit, 19.20...double wave rectifier circuit, 2
1... Aperture, 22... Aperture position detection circuit, 23...
・Zoom lens, 24...Zoom position detection circuit, 25
．． 26...~Φ converter, 27... Microcomputer, 28... Zoom position detection means, 29... Aperture position detection means, 30... BPF selection means, 31.32
...Switch, 33...Semi-high range BPF, 34...
・Very high range BPF0 Name of agent: Patent attorney Toshio Nakao Haka 1st person
11!1 22 Figure 3 WfI precepts Figure 4 Figure 5

Claims (1)

[Claims] A plurality of bandpass filters (BPFs) having different bands and to which optical path modulated outputs are added, a zoom position detection means for detecting the zoom lens position of the imaging lens, and an aperture position detection means for detecting the aperture position; An automatic focus adjustment device characterized in that it is provided with a BPF selection means for selecting an optimal BPF from among the BPFs.