JPS6138916A - Video camera having automatic focus detecting system - Google Patents

Abstract

PURPOSE:To prevent a video output signal from a bad influence due to a driving signal of a projector by forming a high frequency component removing circuit in a light emitting signal generating circuit for the projector. CONSTITUTION:When a switch is closed, synchronizing signal SYNC is applied from an arithmetic processing circuit 16 to synchronization detecting circuits 14a, 14b and a driving signal modulated at its pulse by the light emitting signal generating circuit 17 synchronously with the application of the signal SYNC is removed at its high frequency signal component by the high frequency component removing circuit 18 and applied to the projector 11 to emit a light emitting element 11. The reflected light of the projected spot image is received by photodetecting areas 12A, 12B in the photodetecting element 12 and their outputs are inputted to the circuit 16 through amplifiers 13a, 13b and detecting circuits 14a, 14b to move a coupling optical system to a focusing position through a motor driving circuit 19 and a motor 20. Since the circuit 18 is added, the video output signal can be prevented from a bad influence due to a driving signal for the projector 11.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a video camera having means for automatically detecting the focus of an imaging optical system.

<Prior art> Conventionally, as shown in FIG. 3, an automatic focus detection device for an imaging optical system projects a light spot image from a light projecting element 1 toward an object OB, and splits the reflected light into two. photosensitive area 2A
, 2B, and detects the distance from the light receiving position to the object OB, or detects the focusing state of the imaging optical system. In the figure, it moves in conjunction with the light receiving element 2 and the imaging optical system. That is, as can be easily understood from FIG. Assume that it is formed exactly in the middle of regions 2A and 2B. .

At this time, considering a state where the object OB is at a position S2 further away, the projected light spot image reflected from the object OB is formed at a position closer to the photosensitive area of the light receiving element 2 on the side of the two people. Further, assuming that the object OB is located at a nearby position S3, the projected light spot image reflected from the object OB is formed at a position closer to the photoreceptor 2B side of the light receiving element 2. When in position S1, imaging optics/F L
Assuming that the focusing distance M is on the planned focal plane P (in-focus state), even if the subject OB is at position S2 or S3 and out of focus, the two photosensitive areas of the light-receiving element 2 By comparing the light reception outputs of and 2B, it is possible to know to which side the focal position of the imaging optical system is shifted from the expected focal point □ plane P.

Therefore, by applying this principle, when the imaging optical system is in an out-of-focus state, the photosensitive area 2A of the light receiving element 2.

Depending on the magnitude of the output of the 2B, the imaging optical system is moved along the optical axis in the direction of the in-focus position manually or by a motor or the like. Then, along with the movement 1 of the imaging optical system, the projection direction of the light projecting element 1 and the light receiving direction of the light receiving element 2 are changed, and the projected light spot image is placed exactly in the middle between the photosensitive areas 2A and 2B of the light receiving element 2. If the focal position of the imaging optical system is placed on the planned focal plane when 2B is formed, that is, by detecting that the difference in the received light output between the two photosensitive areas and 2B has become zero, the formation of Focus detection of the image optical system can be performed.

Accordingly, if the difference between the outputs of the photosensitive areas 2A and 2B of the photosensitive element 2 is zero, it is in focus, and if the output of the photosensitive area 2B is thicker than the output of the photosensitive area 2A, the front focus (planned) is achieved. (state where the focus position of the imaging optical system is in front of the focal plane),
If the outputs of the two photosensitive areas are larger than the output of the photosensitive area 2B, then back focus occurs (a state in which the focus position of the imaging optical system is on the rear side of the expected focal plane). And photosensitive area 2A,
Depending on the magnitude of the 2B output, the imaging optical system can be brought into full focus by manually or automatically moving the imaging optical system backward in the case of front focus, or forward in the case of rear focus. This is possible.

By the way, in the above-mentioned device, as shown in the operating signal waveform diagram of FIG.
It is pulse modulated by YNCK and a light emission output IRED is obtained. Also, the area 2A of the light receiving element 2.

The electrical signal obtained from 2B is obtained in the form of a superposition of the reflected light component of the projected infrared light and the external light component of the sun and artificial light,
It has a waveform similar to the signal SPC. This signal is outputted as a signal Amp f by an amplifier with high-pass characteristics, and the output signal Amp is synchronously detected by the synchronizing signal 5YNC, and further integrated to obtain an integrated waveform like the output signal Int, which is applied to the area 2A described above. .

The above-mentioned automatic focus detection is performed using the output signal Int f corresponding to 2B.

<Problems to be Solved by the Invention> In the case of a video camera using such a system, the light emission output IRED shown in FIG. The drawback was that the high frequency signals produced unsightly noise on the monitor screen from the video camera.

SUMMARY OF THE INVENTION It is an object of the present invention to overcome the drawbacks of the prior art described above and to provide an automatic focus detection video camera in which the driving signal of the light projecting element does not adversely affect the video output signal from the camera.

Means for Solving the Problems> The present invention has a light receiving element that receives the reflected light of a pulse-modulated projected spot image projected from a light projecting element onto an object, and outputs an output according to the light receiving position. In a video camera having an automatic focus detection method that performs synchronous detection in synchronization with the modulated pulse and further sets the imaging optical system to a focused position based on the integrated value, the light emitting signal generation circuit of the light projecting element The light emitting element is configured to emit light via a high frequency component removal circuit.

<Description of Examples> The present invention will be described with reference to FIGS. 1 and 2 with regard to examples.

FIG. 1 is a block circuit diagram of an automatic focus detection circuit according to the present invention, and FIG. 2 is an operating signal waveform diagram thereof.

In FIG. 1, numeral 11 is a light projecting element made of an IRED or the like that emits near-infrared light, and projects a light spot image onto an object. 12 is a light receiving element, which is divided into two areas 12A,
12B e, the light projector receives the reflected light from the object of the image and photoelectrically converts it. Amplification circuits 13a and 13b amplify the optical information photoelectrically converted in the regions 12A and 12B, respectively. The amplifier circuit 13a.

13b has sufficient amplification for the modulation frequency of the infrared light projected by the light projecting element 11, which becomes a projected light spot image, and suppresses the amplification as much as possible for the frequency of modulated light from unnecessary sunlight or commercial power supply. It is desirable to use an amplifier circuit that has good frequency characteristics. 1
4a and 14b are synchronous detection circuits that synchronously detect the outputs of the amplifier circuits 13a and 13b, respectively; in this case, the synchronous signal has the same frequency as the light emission drive signal of the light projecting element 11, and has a constant phase. maintaining relationships. 15a
, isb are integrator circuits, each of which is connected to the synchronous detection circuit 1.
The outputs of 4a and 14b are all integrated, and the integral output V is increased moment by moment at an increasing rate proportional to the signal strength of the target signal.
A, VB'e get. Reference numeral 16 denotes an arithmetic processing circuit, into which the integrated voltage VA r VB from the integrating circuits 15a-, 15b is input, performs arithmetic processing for detecting in-focus and out-of-focus states, and based on the results, outputs the motor drive circuit 19. A control signal is sent to the synchronous detection circuit 14 to control the rotation of the imaging optical system driving motor 20, and the synchronous signal 5YNC is transmitted to the synchronous detection circuit 14.
a, 14b, and is also input to the light projecting element light emission signal generation circuit 17. The light emitting element light emission signal generating circuit 17 is connected to the light emitting element 1 via a high frequency component removal circuit 18.
Connected to 1.

Next, its operation will be explained with reference to the operating signal waveform diagram of FIG.

When the starting switch (not shown) is closed, the synchronization signal 5YNC shown in FIG. Generation circuit 1
The drive signal pulse-modulated in step 7 has its high frequency signal component removed by the high frequency component removal circuit 18 in the next stage, and the drive signal is sent to the second stage.
The light emitting signal IRED shown in FIG.

The area 12A of the light receiving element 12 receives the reflected light of the projected spot image projected onto the object from the light projecting element 11 that emitted light in this way,
12B receives the light, detects its output, and moves the imaging optical system to the in-focus position.

<Effects of the Invention> As explained above, the present invention eliminates harmful high-frequency signal components from the video output signal from the video camera by configuring the drive signal for the light emitting element to not include high-frequency signal components caused by pulse modulation. It has the effect of completely removing mixed noise and creating a clear playback screen.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram of an embodiment of a video camera having an automatic focus detection method according to the present invention, FIG. 2 is an operation signal waveform diagram thereof, and FIG. 3 is an explanatory diagram of the configuration of a conventional automatic focus detection device. FIG. 4 shows the final operating signal waveform diagram. DESCRIPTION OF SYMBOLS 11... Light projecting element, 12A, 12B... Light receiving element divided into 2 regions, 13a, 13b... Amplifying circuit, 14a, 14b... Synchronous detection circuit, 15a
, 15b--integrator circuit, 16--arithmetic processing circuit,
17...Light emitter light emission signal generation circuit, 18...High frequency component removal circuit, 19...Motor drive circuit, 20...
·motor. 8 Figure 1 Figure 2 S”/NC

Claims (1)

[Claims] 1. The light receiving element receives the reflected light of the pulse-modulated projected spot image projected from the light projecting element onto the target object, synchronously detects the output according to the light receiving position in synchronization with the modulation pulse, and further integrates the reflected light. In a video camera having an automatic focus detection method that sets an imaging optical system to a focusing position based on a value determined by the value, the light emitting element is configured to emit light via a high frequency component removal circuit in a light emitting signal generation circuit of the light emitting element. A video camera having an automatic focus detection method, characterized in that the video camera is configured as follows.