JPS59111479A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To detect electronically a focal position by moving a lens based on a function obtained by differentiating a video signal. CONSTITUTION:Light from an object passes through a lens 1 and is led to an image pickup section 2, where the video signal is obtained. The video signal is differentiated by a differentiating circuit 3 and the envelope is obtained by a peak detecting circuit 4. The part surrounded by the upper envelope and the lower envelope is integrated timewise by an integration circuit 5. A maximum value control section 6 moves the lens 1 so as to maximize the result of time integral. Since the focus is detected electronically by using a video output signal, the focus is detected correctly even if the lens is replaced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an automatic focusing device for electronically detecting the focus of a television camera among cameras.

Conventional configuration and problems Conventional autofocus devices use some means to measure the distance to the subject and use the results. Since they are independent, they have the disadvantage that they cannot be used interchangeably with any lens.

Another method uses electronic means to detect the focus and move the lens so that the high-frequency portion of the video signal is maximized.

However, with this method of detecting high-frequency components, the high-frequency components are detected over a range of objects with clear links and objects with blurred images, so the detection level is variable beyond the dynamic range of the detection circuit. For example, a variable gain AMP, a counter, a D/A, etc. were required.

OBJECTS OF THE INVENTION The present invention eliminates these drawbacks and makes it possible to perform focus detection using pointer means.

Constituent Structure of the Invention The lens is arranged so that the change in the video signal per unit time of the video signal; It is characterized by automatic focusing.

Description of examples An embodiment of the present invention will be described below.

FIG. 1 is a block diagram of the principle of the automatic focusing device of the present invention. Reference numeral 1 denotes a lens, through which light from a subject passes and is guided to a photoelectric signal conversion (photographing section 1) section 2. A video signal is obtained by performing general conversion processing here. This video signal is differentiated by a differentiating circuit 3, the envelope is determined by a subsequent peak detection circuit 4, the result is time-integrated by an integrating circuit 6, and the maximum value control section 6 calculates the envelope by using an integrating circuit 5. A motor or the like is used to control the movement of the lens 1 in the direction in which the integral value is always larger.

That is, light from the subject passes through the lens 1 and is extracted as a video signal by the opto-electrical signal converter 2. If the upper envelope of 7 obtained by the detection circuit 4, which expresses this video signal as a function v(t), is V+('j) + the lower envelope v2(t), then the integrating circuit 6 calculates ("a (
v+(t)-v2(t))dt=Vab is obtained. Automatic focusing can be performed by moving the lens using a motor or the like so that this integral value Vab becomes maximum.

The block diagram in FIG. 2 is a block diagram showing in more detail the parts covered by the principle block diagram in FIG. 1.

FIG. 3 is a waveform diagram of each part of FIG. 2.

Hereinafter, Maki's embodiment will be described with reference to FIGS. 2 and 3. 7 is a differentiation circuit that differentiates horizontal signals; 8
is a differentiator circuit that differentiates a signal in the vertical direction. 9,1o
is a circuit that peak-detects the differentiated signal, 11.1
2 is the signal inversion time, 13.14 is the peak detection circuit 9
, 10 and the output of the inverting circuit 11.12 are clipped in the positive direction and added together with a clip to calculate υlI, 19 i
f: A/D converter, 16 is a microcomputer, 1
γ is a motor, and 18 is a lens corresponding to the diagram in FIG. 1, which is movable in the direction of the optical axis.

In this configuration, the video signal a obtained from the photoelectric converters of lenses 1 and 2 shown in FIG.
Differentiate with a time constant of about 01 to 06 horizontal synchronizing signal period (b). On the other hand, the differentiating circuit 8 differentiates with a time constant of about 0.5H to 4H. If the video signal obtained now has a waveform as shown in a of FIG. 3, the differential waveform will be as shown in b. This is peak-detected and the envelope of the differential signal is obtained as shown in C. On the other hand, the inversion circuit 11 inverts the signal as shown in d, and the clip addition circuit 13 clips, for example, the lower side and adds only the upper side. This waveform corresponds to e. The addition signal e thus obtained is digitized by the '/n converter 15 and applied to the microcomputer 16. The computer performs integral calculations and issues a command to the motor 17 to move the lens 18 so that the integral value becomes larger.

In this case, the A/D converter 15 converts the output of the clip adder 14 during a certain timing "V" as shown in f in FIG. A/D converts the output.

FIG. 4 shows another embodiment in which two of the 15'/D converters shown in FIG. 1 are used, one for horizontal and one for vertical. Here, 19.20 is a differential circuit, each with 2
1.22 peak detection circuits are connected, and the outputs of the peak detection circuits 21 and 22 and the signals passed through the 23+24 inversion circuits are respectively connected to the 25.26 clip adder circuits. The added signal is sent to the A/D converter 27.2
8. Microcomputer 3 through adder 29.30
Connected to 1. The lens 33 is moved and assisted by a microcomputer 31 via a motor 32.

Effects of the Invention The present invention has the above configuration, and according to the present invention, the following effects can be obtained.

Since the focus is detected by electronic means from the image output, it has the advantage that it can be used interchangeably with any lens. Another advantage is that mechanical position adjustment of the optical system is unstable unless optical components such as a half mirror are used. Furthermore, compared to methods that measure the distance to a subject by emitting radio waves, ultrasonic waves, etc., this method allows accurate focus detection even when using a zoom lens, and has the advantage of not being affected by wind or the like.

It should be noted that the envelope function may be designed to take the minimum value of the differential value for time integration.

[Brief explanation of drawings]

Fig. 1 is a principle block diagram of an automatic focusing device according to an embodiment of the present invention, Figs. 2 and 4 are specific block diagrams of the same essential parts, and Fig. 3 is an operation waveform diagram of Fig. 2. It is. 1... Lens, 2... Optical air signal conversion, 3... Differentiation, 4... Peak detection, 5...
...Integration, 6...Maximum value control, 7,19
...Horizontal differential, 8,20...Vertical differential, 9,10.21.22...Peak detection circuit, 11,12.231 24... - Inversion circuit, 13, 14, 25.26... Clip addition circuit, 15.27. 28...), /D converter, 1
6゜31・・・Microcomputer, 17,3
2... Motor, 18133... Lens, 29.30... λ Figure 21!1 Figure 3 Figure 4

Claims (2)

[Claims] (1) The image signal obtained by converting the light from the object that has passed through the lens into an electrical signal in the imaging unit is differentiated, and the envelope function connected at the maximum or minimum value of this differential value is time-integrated. , an automatic focusing device characterized in that the lens is moved so that the integral value thereof is maximized. (2) The automatic focusing device according to claim 1, wherein the maximum and minimum differential values are determined separately for horizontal and vertical components.