JPS63181571A - automatic focusing device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an automatic focusing device that drives a lens focusing device so that the high frequency component of an electrical signal obtained from an image sensor of a video camera is maximized. It is.

2. Description of the Related Art Conventional automatic focusing devices include, for example, the Japanese Patent Publication No. 43-
It is shown in Japanese Patent No. 91944. FIG. 3 shows a block diagram of an automatic focusing device that operates almost the same as the conventional device. 1 is a lens; 2 is an image sensor that converts the object image formed on the imaging surface into an electrical signal; 3 is a preamplifier that amplifies the electrical signal obtained from the image sensor 2; 4
6 is a process circuit that applies various processing to the output of the preamplifier 3 to produce a television signal; 6 is a synchronization signal generator that supplies a blanking signal etc. to the process circuit 4 and the image sensor drive circuit 6; 6 is the image sensor 2; For example, it is composed of a bandpass filter with a center frequency of I MHz and an amplifier. Reference numeral 8 denotes a reference frequency component detection circuit for detecting a reference frequency component from the high frequency components, and is composed of a bandpass filter.

Reference numeral 9 is a reference frequency generator, which outputs the reference frequency to the synchronous detection circuit 1.
0 and also to the motor drive circuit 11,
The focusing device of the lens 1 is slightly changed by a motor 12 to change the focus of the lens 1 to an extent that cannot be detected by the eye. Due to the above change, the high frequency component has a reference frequency component. 1° is a synchronous detection circuit that detects the amplitude and phase of the reference frequency component detected by the reference frequency component detection circuit 8 at the reference frequency, applies the detection signal to the motor drive circuit 11, and outputs the high frequency signal obtained from the image sensor 2. The motor 12 is driven so that the component is maximized.

The operation of the conventional automatic focusing device configured as described above will be described below with reference to FIG. 4.

In FIG. 4, the horizontal axis indicates the position of the focusing device of the lens 1; near is the position where a near object is in focus, and far is a position where a far distance subject is in focus. The vertical axis is
It shows the amplitude of the high frequency component of the electrical signal obtained from the image sensor 2.

Now, assume that the distance to the subject is D. At this time, when the focus adjustment device of the lens 1 is at position d corresponding to the distance, the focus will be aligned and the high frequency component will be at its maximum. However, the high-frequency components are reduced, resulting in a mountain-shaped characteristic. Further, al and a2 indicate movements of the focusing device due to slight fluctuations in the reference frequency of the motor 12. al indicates a slight fluctuation when the focusing device of the lens 1 is located at the short distance side of position dj, and at this time, the high frequency component undergoes amplitude modulation as shown by b1 due to the said slight fluctuation. a2 is on the far side, in this case b2
It undergoes amplitude modulation like . Said b1. As is clear from the figure, the phase of the amplitude modulation of b2 is reversed depending on whether the focusing device is located closer or farther than the focal point. Therefore, the signal bl is synchronously detected at the reference frequency, and the motor 12 is driven in the direction of the arrow c1 using the synchronously detected signal. Furthermore, the signal b2 does not drive in the direction of the arrow c2, but remains stable at the point where the high frequency component is always at its maximum.

Problems to be Solved by the Invention However, the above configuration has the following problems.

The image sensor successively integrates electrical signals generated by inputting light for a certain period of time, and then outputs them using a predetermined method. For example, when using a COD as an image sensor, 1/60
There is a field accumulation mode with an accumulation time of seconds and a frame accumulation mode with an accumulation time of 1/3o seconds. moreover,
Recently, video cameras have been commercialized that are equipped with an electronic shutter mode with an accumulation time of 1/100 seconds, for example, in order to take pictures of fast-moving subjects without any prerequisites.

Now, the fundamental frequency 18 mentioned above is expressed as f, = sin (2rr t fy/4), (fy
: Vertical scanning frequency)... (1) When set to (1), the amplitude modulation that the high frequency component included in the electrical signal obtained from the image sensor receives is calculated by the following formula: % AH: Amplitude of the high frequency component Therefore, ( 2) When the point where the second term of the equation is maximum is at the center of the storage time, the amplitude modulation degree of the high frequency component is maximum. Also, when the accumulation time becomes shorter, the amplitude A of the high frequency component
H will continue to decrease.

In the conventional method, the phase of the reference frequency f is fixed, so when the accumulation time becomes short, the amplitude of the high frequency component and the degree of amplitude modulation decrease, and the function as an automatic focusing device is sufficiently performed. I can't.

In view of this, it is an object of the present invention to provide an automatic focusing device that does not deteriorate the automatic focusing function caused by a decrease in the degree of amplitude modulation of high-frequency components due to changes in the storage time of the image pickup device described above.

Means for Solving the Problems The present invention includes an imaging device that converts optical information of a subject into an electrical signal, and a method that periodically and optically modulates the subject image formed on the imaging surface of the imaging device. means for generating a reference signal for periodic and optical modulation; detecting the phase and amplitude of the reference signal component included in the high frequency component of the electrical signal from the image sensor; means for driving a focusing device of a lens so as to maximize the focus of the lens; means for controlling the phase of the reference signal for periodic and optical modulation in accordance with changes in the accumulation time of the image sensor; This is an automatic focusing device that has means for controlling the gain of high frequency components according to the accumulation time of the element.

According to the above configuration, the present invention controls the phase of the reference frequency and the gain of the high frequency component, accurately detects the phase and amplitude of the reference frequency component included in the high frequency component at the reference frequency, and improves the storage of the image sensor. It makes it possible to achieve a sufficient focusing function regardless of time.

Embodiment FIG. 1 shows a block diagram of an automatic focusing device according to an embodiment of the present invention, and blocks that are the same as those in the conventional configuration shown in FIG. 3 are given the same reference numerals. 13 is a phase controller that controls the phase of the reference frequency output from the reference frequency generator 9; 14 is a gain control circuit that controls the gain of the high frequency component of the video signal detected by the high frequency component detection circuit 7; be. Reference numeral 15 denotes a circuit for changing the storage time of the image pickup device, such as a switch for changing between the field storage mode (60 seconds) and the electronic shutter mode (Hamaun Takukan).

The operation of the automatic focusing device of this embodiment configured as described above will be described below with reference to FIG. 2.

FIG. 2 shows the timing of charge readout in the field accumulation mode and electronic shutter mode when a COD is used as the image sensor. In addition, the optimum fundamental frequency waveform for each mode is also shown.

Now, when the accumulation time changeover switch 16 of the image sensor is in the field accumulation mode, the reference frequency output from the reference frequency generator 9 is set at the center of the vertical scanning period (the accumulation time The phase is controlled by the phase controller 13 so that the peak appears at the center of

Next, when the accumulation mode of the image sensor is switched to the electronic shutter mode, the reference frequency is controlled by the phase controller 13 so that its peak appears at the center of the accumulation time in the electronic shutter mode, as shown in FIG. be done. Also,
In electronic shutter mode, the lens aperture is opened to prevent the video signal level from decreasing, but if the subject illuminance is low, sufficient correction cannot be made. In such a case, the gain control circuit 14 controls the gain of the high frequency component to accurately detect the phase and amplitude of the reference frequency component.

Therefore, according to the present embodiment, it is possible to eliminate the deterioration of the automatic focusing function caused by the phase shift and decrease in amplitude of the reference frequency component due to the accumulation time of the image sensor.

As described in detail, according to the present invention, it is possible to realize an automatic focusing device in which the automatic focusing function does not deteriorate due to a phase shift and a decrease in amplitude of the reference frequency component due to the accumulation time of the image sensor. It can be done, and its practical effects are great.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an automatic focusing device according to an embodiment of the present invention, FIG. 2 is a diagram for explaining the operation of the same embodiment, FIG. 3 is a block diagram of a conventional automatic focusing device, and FIG.
The figure is a diagram for explaining the operation of the conventional example. 1...Lens, 2...Image sensor, 7.
. . . High frequency component detection circuit, 8 . . . Basic frequency component detection circuit, 9 . . . Reference frequency generator,
1o: Synchronous detection circuit, 12: Motor, 13: Phase controller, 14: Gain control circuit, 15: Imaging Element accumulation time selection switch. Name of agent: Patent attorney Toshio Nakao and 1 other person! @
2 Figure 4

Claims (1)

[Claims] a reference signal generation circuit for periodically and optically modulating a subject image formed on an imaging surface of an image sensor whose accumulation time can be selectively changed; a circuit for changing the phase; a circuit for detecting a high frequency component of the output signal of the image sensor; a circuit for detecting a modulation component due to the periodic optical modulation from the high frequency component; An automatic focusing device comprising a circuit for synchronous detection, and driving a lens focusing device so that the high frequency component is maximized by the synchronous detection output.