JPS62168105A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To perform smooth focusing control and to increase a dynamic range by varying the quantity of light emitted from a light emission part which projects infrared light as spot light stepwise with the integration time of an integration circuit which integrates the detection output of a photodetecting element. CONSTITUTION:Two output currents of a semiconductor position detector(PSD) are converted by current-voltage converters 1 and 1' into voltages, and signal voltages VA and VB generated by integration circuits 3 and 3' are converted into digital values by and A/D converter 4. Then, a logic circuit or microcomputer 5 performs arithmetic VA+VB corresponding to the quantity of photodetection of the PSD and controls an integration time and the quantity of light emission of a light emitting LED 7 with th arithmetic value. Pulse modulation is imposed upon the light emitted by the LED 7 and the integration time is controlled by controlling the number of pulses to be integrated by the microcomputer 5, etc. Thus, the smooth focusing control is performed and the dynamic range can be increased.

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Field of Industrial Application) The present invention relates to an automatic focusing device such as a camera, and more particularly to a so-called active automatic focusing device that projects light onto a subject.

(Prior Art) Among autofocus devices such as cameras, so-called active autofocus devices in which the camera has a light source, projects light onto the subject, and detects the reflected light to detect the distance to the subject. The amount of received light changes significantly depending on the distance to the subject and the reflectance of the subject, and may exceed the processing level of the light receiving element or signal processing circuit.

Conventionally, two countermeasures have been attempted as countermeasures against this problem.

First, as shown in FIG. 4, the output current I2 of the semiconductor device detector (PSD) 11 is converted into a voltage V2 by a current-voltage conversion circuit 12.13.
The integration circuits 14 and 15 integrate the time determined by the integration time control circuit 18, and input the integrated value 8, Vo to the addition circuit 16 to obtain V^+Va, and at the same time input it to the subtraction circuit 17 to obtain V Obtain the position information of the subject from ^-Ve. On the other hand, since V A + V a indicates the amount of light received by the PSD, this value is input to the integration time control circuit 18, and the integration time is determined so that this value becomes a predetermined level that allows distance measurement. (Japanese Unexamined Patent Publication No. 57-44809) This method has the following features: (1) If the object is far away and has a low reflectance, the integration time becomes longer, and the control time required to achieve focusing becomes longer, making it difficult to achieve smooth focusing.

■ If the integration time is long, the influence of noise light will increase, making it impossible to obtain accurate and highly accurate distance measurement information.

■ If an attempt is made to increase the intensity of the projected light and increase the amount of reflected light in order to shorten the integration time, the light-receiving scene will become excessive on the short-distance side and may exceed the capacity of the light-receiving element or circuit system. Even if such a problem does not occur, when a battery is used as a power source, the problem arises that power consumption is too large.

■ When the integration time becomes longer, the offset shift of the integration circuit affects the ranging information, so highly accurate adjustment is required.

There is a problem.

Another method is the PSD20, as shown in the control circuit in Figure 5.
The output currents 1 and 2 are converted into a current-voltage conversion circuit 23.2
4, and input the integrated voltages V^ and VB to the subtraction circuit 25 to obtain position information from V^-Va, and adder circuit 26
This value is input to the light emitting light amount control circuit 27, and the light emitting amount is determined to be at a predetermined level that allows distance measurement, and the first light is emitted.

(Japanese Unexamined Patent Publication No. 58-87543) This method has the following features: ■ Adjusting only the change in luminous intensity has a limit not only on the light source itself, but also in terms of power consumption when using a battery as a power source. Therefore, there are limits to the distance measurement range.

■ A device that feeds back the incident intensity to continuously change the emitted light intensity is complicated and increases cost.

■ If a strong light emission pulse is generated momentarily, the resulting noise may enter the signal processing system of the video camera, affecting the image or causing malfunction.

It includes problems such as.

(Problems to be Solved by this Invention) In general, the conditions required for an automatic focusing device are: ■ Short focusing time and smooth control; ■ Accurate distance measurement system and high-precision distance information. What can be achieved ■ Has a wide ranging range ■ Has low energy consumption ■ Has a simple circuit and control method ■ Has low cost ■ Can be easily adjusted. An attempt is made to obtain an automatic focusing device that satisfies the above conditions.

Structure of the Invention Means for Solving Problem C) The automatic focusing device of the present invention includes a light emitting section that emits infrared light of a specific frequency, a light projection optical system that projects the infrared light as a spot light, A light receiving system that forms an image of the reflected light from the subject of the spot light on a position detection element, a detection circuit that detects two output signals of the position detection element in synchronization with a specific frequency of the light projection, and a detection circuit of the detection circuit. an integrating circuit that integrates the output; a computing unit that computes the output of the integrating circuit to detect an imaging position on the position detection element corresponding to the blurred distance to the subject; and a control unit that controls driving of a focusing lens, and the light emitting portion is characterized in that the amount of light emitted by the light emitting portion can be changed discontinuously in multiple stages depending on the integration time of the integrating circuit.

More specifically, the integration time is controlled by the amount of received light,
If the integration time becomes longer than the predetermined longest integration time due to a decrease in the amount of received light, the amount of emitted light is changed to one step brighter and the integration time is changed to the predetermined minimum time. When the integration time becomes shorter than the shortest integration time, control is performed so that the amount of emitted light is changed to one step darker and the integration time is changed to a predetermined minimum time.

(Embodiment) FIG. 1 shows an embodiment of a control circuit for an automatic focusing device of the present invention.

The two output currents of the PSD are converted into voltage by the current-voltage converter 1.1', and the detection circuit 2.2' and the integrating circuit 3.3
After converting the signal voltages V^ and Va, which are generated by ', into digital values by the A/D converter 4, the logic circuit or microcomputer 5 calculates V A + Ve corresponding to the amount of light received by the PSD. , the integration time and the amount of light emitted from the light emitting LED 7 are controlled by this calculated value.

The light emission of the LED 7 is performed by pulse modulation, and the integration time is determined by controlling the number of pulses to be integrated using a microcomputer 5 or the like. For example, if the amount of light received by the PSD decreases, the value of V^+v8 decreases. At this time, the integration circuit 3
increases the number of pulses to be integrated according to the command from microcomputer 5.

Keep the value of V^+VB within a range that allows accurate distance measurement. When the integration time, that is, the number of pulses exceeds a preset number, the amount of light emitted by the LED is increased by one step,
Integration is performed for the minimum number of pulses corresponding to the preset amount of emitted light. This will be explained with reference to FIG. 2. The vertical axis in FIG. 0 indicates the amount of light emitted from the LED, and the amount of light emitted is discontinuously controlled over a plurality of predetermined stages of A, B, and C. The horizontal axis indicates the number of pulses to be integrated, and a minimum number n, n, and a maximum number are set corresponding to each amount of light emission. Now, measure at point P, V^+v
If the value of e is low, the number of pulses to be integrated is increased and the measurement conditions are moved horizontally to the right along the solid arrow. When the number of integrated pulses reaches n4, the amount of one emitted light changes to step C, and at the same time, the number of integrated pulses is set to the minimum number of pulses n3 at step C. In this case, it goes without saying that n4×b ≧ n, Xc and similarly n4×a ≧ n, Xb are selected.

Conversely, if the amount of light received by the PSD increases, V^+Va
The value of increases. In this case, move to the left along the dotted line in FIG. 2 and decrease the V^+VB value. When the number of pulses becomes smaller than the set minimum value n2, the amount of light emission is changed to a level one step lower, and the minimum number of pulses n1 corresponding to the level a is set.

FIG. 4 shows a flowchart for setting the amount of emitted light and the number of pulses when the amount of emitted light is controlled in three stages.

In this automatic focusing device, it goes without saying that the setting of the minimum number of pulses at a certain level of light intensity is selected so that the amount of received light does not exceed the ability of the PSD or the circuit system at that amount of emitted light.

Effect of the invention This invention has the above configuration.

■ The integration time does not exceed the set maximum number of pulses, n.
Control is smooth because the distance is always measured within a certain range of time.

- Since both the amount of emitted light and the integration time are changed, the amount of light received by the PSD is within the range within a wide distance measurement range, and the dynamic range of the system is widened.

[Yes] Multi-stage light emission control allows no wastage of energy consumption.

■ Control is easy by using an A/D converter, a microcomputer, etc., and the amount of light emitted is also controlled in stages, making the circuit configuration simpler and cheaper than continuous control.

■ The negative effects of excessive integration time, such as deviations due to offset and noise fluctuations, can be removed.
High precision adjustment becomes unnecessary.

It has remarkable effects such as

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the automatic focusing device of the present invention, FIG. 2 is a graph showing a method of controlling the amount of emitted light and integration time, FIG. 3 is a flowchart thereof, and FIGS. FIG. 5 is a block diagram showing the configuration of a conventional example. 11.20: PSD 1.12.13.21.22: Current-voltage converter
2: Detection circuit 3.14.15.23, 24: Integrating circuit 4: A/D
Converter 5: Microcomputer 16.25: Adder circuit 17.
26-Subtraction circuit 6.27: Light emission, light amount control circuit 18: Integral time control circuit 7.19.28: Light emitting LED Patent applicant Konishiroku Photo Industry Co., Ltd. Applicant's agent Patent attorney Fumio Sato (and 2 others) No. 1 Figure 2

Claims (1)

[Claims] a light emitting unit that emits infrared light of a specific frequency; a light projection optical system that projects the infrared light as a spot light; a light receiving system that forms an image of the reflected light from the subject on the position detection element;
a detection circuit that detects each of the two output signals of the position detection element in synchronization with a specific frequency of the light projection; an integration circuit that integrates the output of the detection circuit; and a distance to the object by calculating the output of the integration circuit. and a control section that controls driving of a focusing lens based on the detection information of the calculation section, and the light emitting section is connected to the integration circuit. An automatic focusing device characterized by being able to discontinuously change the amount of emitted light in multiple stages depending on the integration time.