JPH0583843B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a floodlight type distance measuring device suitable for a camera, and more particularly to a technique for preventing malfunctions in close distance measuring.

(Prior art) An automatic focus adjustment device used for small cameras such as still cameras and video cameras has a light projecting part A at one end of the camera body and two light projectors at the other end, as shown in Figure 4A. A light-receiving section B is provided by connecting two light-receiving elements B ₁ and B ₂ in antiparallel, and _the light-receiving section B is scanned in conjunction with the focusing mechanism of the photographic lens _. The signal level at the time when the signal intensities from the two sides match is set as the reference voltage Vs, and the point at which they match is set as the in-focus point (FIG. 4B).

By the way, when the distance between the camera and the subject is reduced to about 0.5m, the subject S
The intensity of the reflected light beam increases. Therefore, at the same time that a light spot is formed on one photodetector _B1 , a strong light beam is incident on the other photodetector _B2 , and the reference voltage is set at the initial point, that is, when the photographing lens is located at the shortest focal point. Vs
The output signal exceeds the output value. Even in such a state, the light receiving section is scanned toward the infinity point in order to find the balance point, but the problem is that the balance point cannot be found and it sticks to the infinity point, resulting in a large focus shift. It was hot.

Furthermore, for example, in the configuration disclosed in Japanese Patent Application Laid-open No. 59-87314, if there is a subject with high reflectance, the signal light enters the light-receiving element at high brightness during light projection and saturates the element, so the distance signal of the subject is The lens is extended to a very close position without any regard. On the other hand,
In the present invention, since the two light-receiving elements cancel each other's output currents, the correct distance is output without being affected by the brightness of the subject, and the subject is not determined to be very close to a subject with high reflectance.

(Purpose) In view of these problems, the present invention provides a projection system that can stop scanning as close as possible, regardless of the presence or absence of a focus signal, when the distance between the subject and the camera is extremely short. The purpose is to provide an optical distance measuring device.

(Structure) Therefore, details of the present invention will be described below based on illustrated embodiments.

FIG. 1 shows an embodiment of the present invention, in which reference numeral 1 denotes a distance measuring optical system, which receives pulsed power from a drive circuit 2 and intermittently irradiates a light beam onto a subject S. a light emitting unit 3 and two light receiving elements 4a.
and a light receiving element 4b are connected in antiparallel, and the light receiving section 4 moves on a base line in conjunction with the extension and retraction of the photographic lens 5 of the camera body.
7 is a synchronous rectifier circuit, which receives the signal from the amplifier circuit 6,
A signal from a reference signal generator 8, which will be described later, is input,
It is configured to rectify the received light signal in synchronization with the blinking timing of the light projecting section 3. Reference numeral 8 denotes the reference signal generator described above, which is configured to output a clock signal of a constant frequency to intermittently light up the light projector 3, and output a clock pulse as a reference signal for the synchronous rectifier circuit 7. . Reference numeral 9 denotes an integrating circuit, which is composed of a resistor R and a capacitor C, and converts the pulsed signal output from the synchronous rectifier circuit 7 into a DC signal. Reference numeral 10 denotes a first comparator that detects the in-focus point; one input terminal receives the signal from the integrating circuit 9, and the other input terminal receives the reference voltage _V1 from the reference voltage generation circuit 11, and It is configured to output an L signal at the time of focus.
12 is a second comparator for detecting a close distance; one input terminal receives the signal from the integrating circuit 9, and the other input terminal receives the signal from the distant focus side, in this example, the high level side, by means of a first reference voltage. The set second reference voltage V ₂ is input from the reference voltage generation circuit 11, and the output terminal is connected to the set terminal of the flip-flop circuit 13. Reference numeral 14 denotes a solenoid for stopping the movement of the photographic lens, which is energized at the start of the distance measuring operation, and deenergized when the flip-flop 13 is reversed to stop the movement of the photographic lens. Note that reference numeral 15 in the figure indicates a switching transistor 15 that is turned off when the flip-flop 13 is inverted.

The operation of the apparatus configured as described above will be explained based on the timing diagram shown in FIG.

() When the subject is not located at a close distance When the release button on the camera body (not shown) is pressed and the operating voltage is supplied to the device, light emission starts and after a predetermined period of time, the flip-flop 13 is set to the initial state and the solenoid 14 energize. At the same time, the light projector 3 irradiates a light beam toward the subject S with a constant frequency, and the motor M operates to scan the light receiver 4 over the baseline length from the near focus to the infinity point. . Since the object is not in focus at this point, the reflected light from the subject S enters only one of the light receiving elements 4a forming the light receiving section 4. Therefore, the light receiving section 4 outputs an alternating current signal with a large amplitude that alternates in accordance with the blinking cycle of the light projecting section 3. A synchronous rectifier circuit 7 extracts a component related to the light beam from the light projector 3 from this AC signal, and an integration circuit 9 converts it into a DC signal.

In this state, when the light receiving section 4 is moved in the focusing direction, the other light receiving element 4 of the light receiving section 4
Since the reflected light from the subject S also begins to enter b, the output of one light receiving element 4a is canceled out by the output of the other light receiving element 4b, and the output level from the integrating circuit 9 increases monotonically. When the photographing lens 5 reaches the focal point, the output signal from the integrating circuit 9 matches the first set voltage _V1 , and the first comparator 10 outputs an L signal, that is, a focusing signal. The flip-flop 13 receives this focusing signal, reverses itself, deenergizes the solenoid 14, and stops the movement of the photographic lens 5. This stops the level increase of the output signal from the integrating circuit 9. Therefore, the output voltage from the integrating circuit 9 cannot rise to the second reference voltage _V2 , and the second comparator 12 is not inverted.

() When the subject is located at a close distance The light projector 3 flashes at a constant frequency and emits a light beam toward the subject S. The light beam reflected from the subject S forms a light spot on one of the light receiving elements 4a constituting the light receiving section 4.

In this case, since the subject S is located at a very close distance, the light beam scattered by the subject S has a high level and enters the other light receiving section 4b. As a result, even when the photographic lens 5 is in its initial state, that is, at its shortest focus,
The integrating circuit 9 has already outputted a signal at a level exceeding the first reference voltage _V1 . For this reason, the first
The comparator 10 scans the light receiving section 4 toward the long-distance focal point in search of a balance point without having the opportunity to be reversed. As a result, the level of the output signal from the integrating circuit 9 starts to rise, but immediately reaches the second reference voltage _V2 , the second comparator 12 is inverted, and the flip-flop 13 receives the signal from the second comparator 12. In response, the solenoid 14 is reversed, and the solenoid 14 is deenergized, stopping the movement of the photographic lens 5 and preventing unnecessary movement toward the infinity point.

FIG. 3 shows a second embodiment of the present invention, in which the signal from the second comparator 12 is passed through the inverter 16 to the set terminal, and the signal from the first comparator 10 and the reset signal are input to the second terminal. A flip-flop is provided and a signal from an oscillator 19 is supplied to a light emitting element 20 via an AND gate 18 to issue a warning when the object is at close range. Note that 21 in the figure indicates a switching element.

According to this embodiment, when the photographing lens focuses on a subject during medium or long distance distance measurement, the first comparator 10 inverts and outputs an L signal, inverts the first flip-flop 13 and operates the lens. to stop. At the same time, the L signal from the first comparator 10 causes the second flip-flop 17 to become non-inverted via the AND gate 16. As a result, no signal is output from the second flip-flop 17, and the light emitting element 2 for warning display
0 remains inactive.

On the other hand, during close distance measurement, since the integrating circuit 9 has already output a signal at a level exceeding the first reference voltage _V1 in the initial state, the first comparator 10 outputs an inverted signal, that is, an L signal. There isn't. In this state, the light receiving section 4
When scanning starts, the integrating circuit 9 outputs a signal whose level increases in proportion to the scanning amount. In this way, when the signal from the integrating circuit 9 matches the second reference voltage V ₂ , the second comparator 12
is inverted and outputs an L signal. This L signal causes the first flip-flop 13 to reverse, deenergize the solenoid 14, and stop extending the photographic lens 5. At the same time, the inverted signal of the second comparator 12 is input to the second flip-flop 17 via the inverter 16, the gate 18 is opened, and the signal from the oscillator 19 causes the alarm light emitting element 20 to be activated.
is decremented to notify the user that there is a possibility that the photographing lens 5 may be slightly out of focus.

(Effects) As explained above, according to the present invention, the second reference voltage is set at a level on the far side than the reference voltage for detecting the in-focus point, and the signal from the integrating circuit matches the second reference voltage. Since the photographic lens extension operation is stopped even at this point, it is possible to prevent the photographic lens from running out of control when photographing a subject located at a close distance, and to obtain an image that is close to being in focus. Further, according to the present invention, since an alarm is issued when the signal from the integrating circuit matches the second reference voltage, it is possible to prompt the user to perform a manual focusing operation.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a device showing an embodiment of the present invention, FIG. 2 is a waveform diagram explaining the operation of the same device, and FIG. 3 is a block diagram of a device showing a second embodiment of the present invention. and Figures 4A and 4B are an explanatory diagram and a waveform diagram showing the principle and operation of the floodlight distance measuring device, respectively.
5A and 5B are an explanatory diagram showing the relationship between irradiated light and reflected light at close range, and a waveform diagram showing the output signal, respectively. DESCRIPTION OF SYMBOLS 1... Distance measuring optical system, 3... Light emitter, 4... Light receiving part, 4a, 4b... Light receiving element, 9... Integrating circuit,
DESCRIPTION OF SYMBOLS 10... First comparator, 11... Reference voltage setting circuit, 12... Second comparator, 14... Scan stop solenoid, 20... Close distance warning light emitting element.

Claims (1)

[Scope of Claims] 1. Light projecting means for intermittently irradiating light at a constant frequency, and two light receiving elements connected in antiparallel and moving from the light projecting means at a certain baseline length. a photographic lens system for photographing a subject; a moving means that scans the light receiving element in the base line length direction and moves the photographic lens system in the optical axis direction in conjunction; and a signal from the light receiving means. circuit means for synchronously rectifying according to the frequency and outputting a DC signal; a first comparison means in which a first reference voltage equal to the level of the DC signal at the time of focusing is set; and a side farther from the first reference voltage. 1. A floodlight type distance measuring device, comprising: a second comparing means for determining when the focus is defocused. 2. The camera according to claim 1, further comprising means for stopping the photographing lens by using signals from the first and second comparison means accompanying scanning of the light projecting element as a focusing signal. A floodlight type distance measuring device.