JPS59192215A - Light emission controller for focusing device - Google Patents

Abstract

PURPOSE:To reduce the power consumption and to improve the precision of focusing by switching the quantity of emitted light in a light emitting part in accordance with the output of a light receiving part. CONSTITUTION:A reflected light from an object is condensed on a photodetector 16 in a light receiving part 10 by a condenser lens. The photodetector 16 has a function of photoelectric conversion and outputs photocurrents Ia and Ib condensed by the condenser lens. These photocurrents Ia and Ib are inputted as outputs of the light receiving part to an operating circuit 20 through current-voltage converting circuits 17a and 17b, etc. The moving direction of a photographic lens 26 is calculated in the operating circuit 20, and this signal is outputted to a lens driving circuit 21. The lens driving circuit 21 performs focusing on a basis of the output signal of the operating circuit 20 to focus the lens. Thus, the quantity of current in the photodetector is switched to reduce the power consumption and improve the precision of focusing.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a light emission control device used in an automatic focusing device in a video camera or still camera that emits light toward a subject.

2. Description of the Related Art Structures and Problems There have been various proposals regarding focus adjustment devices for cameras. As one of the most powerful methods,
The subject to be photographed (hereinafter abbreviated as subject),
Projecting a focus adjustment signal such as infrared rays, receiving the focus adjustment signal reflected by the object, and determining the distance to the object or the moving direction of the photographic lens for focusing by the focus adjustment signal. There is a method (hereinafter referred to as an accu-dip focusing method) in which the image formed by the photographic lens is brought into focus by calculating and driving the photographing lens or a part of the photographing lens based on the result.

FIG. 1 shows the principle of an active focusing system using infrared rays. To explain this, infrared light projected from the light emitting section 1 passes through the converging lens 2, reaches the subject 3, is reflected, passes through the converging lens 4, and enters the light receiving section 5. At this time, when the distance between the light emitting section 1 and the light receiving section 6 and the subject 3 changes, the angle of incidence of the reflected light from the subject 3 on the light receiving section 5 or the angle of incidence of the reflected light on the light receiving section 5 changes. The focal point of the light changes. Based on the incident angle or condensing position of this reflected light, the calculation unit 6 calculates the distance to the subject 3 or the moving direction of the photographing lens 8 for focusing. The lens driving device drives the photographic lens 8 or a part of the photographic lens 8 by 1 based on the calculation result of the calculation unit 6, and focuses the image formed by the photographic lens 8, completing the focus adjustment. do.

The active focus adjustment method is less susceptible to the effects of ambient light during shooting, and the directivity angle of the light projected from the light emitting unit toward the subject can be made relatively narrow, making it possible to accurately identify the subject to be photographed. This is a powerful focusing method because it can be used to adjust the focus. However, with the above configuration, when the subject is located far away or the subject has a low reflectance to the light projected from the light emitting part, the reflected light returns to the light receiving part from the subject. This has the disadvantage that the intensity of the signal is insufficient, and a sufficient signal for focus adjustment cannot be secured, resulting in the image formed by the photographic lens being out of focus. In addition, increasing the amount of light emitted from the light emitting part to a sufficient level to solve the above problems would lead to an increase in power consumption, and video cameras and still cameras that require battery operation for portability reasons. This is a serious problem for a focus adjustment device for

OBJECTS OF THE INVENTION It is an object of the present invention to provide a light emission control device used in a focus adjustment device that can reduce power consumption and improve focus adjustment accuracy.

Structure of the Invention A light emission control device for a focus adjustment device according to the present invention includes a light emitting unit that projects a light beam for focus adjustment onto a subject, and a light emitting unit that emits a light flux for focus adjustment onto the subject from the light emitting unit. a light receiving section that receives reflected light and performs photoelectric conversion; a comparison circuit that compares the output level from the light receiving section with a predetermined constant reference level; and a light emission amount that increases the amount of light emitted according to the output from the comparison circuit. The device includes a drive control section that determines whether to give the light emitting section a signal that causes it to emit light again a certain number of times within a certain period of time, thereby reducing power consumption and improving focus adjustment accuracy. This realizes a focus adjustment device that can increase the focus.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 2 is a block diagram of an embodiment of an active focusing device employing the light emission control device of the present invention. Third
This figure is a timing chart in the embodiment of FIG. 2. In FIG. 2, 8 is a light emitting element L E
D (light emitting dio
This is a light-emitting part using de). 9 is a drive control unit, 19
1 is a comparison circuit, and 10 is a light receiving section.

The operation of the light emission control device of this embodiment configured as described above will be described below. First, when attempting to perform focus adjustment, the LED switch signal signal generating section 151.
A pulsed LED switch signal (hereinafter abbreviated as a switch signal) SW shown in FIG. 3 is sent to the drive control section 9. This switch signal SW is input to the AND circuit 13 together with the output G of the gate circuit 14 in the drive control section 9, but since G is normally set to the ON state, the switch signal SW is directly input to the LED drive circuit. 12a. The LED drive circuit 12a receiving this signal drives the LED
A pulse-like signal L1 shown in FIG. This signal L1 turns on the transistor 25 in the light emitting section. At this time, if the voltage applied to the terminal 26 is Vcc, the collector-emitter saturation voltage of the transistor 25 is VsaN, and the resistance value of the resistor 23 is R1, then vcc −Vsat l 11= , −1 −−−−−− - 1 electric current 1 flows to LEDll, and LEDll emits pulsed light. The pulsed light is passed through a converging lens (not shown)
The pulsed light is projected onto the subject through the pulsed light, and the reflected light of the pulsed light from the subject reaches the light receiving section 10. The reflected light is transmitted to the light receiving element 16 in the light receiving section 10 by a condensing lens (not shown).
The light is focused on the top.

The light-receiving element 16 has a function of photoelectric conversion, and outputs photocurrents 1a and Ib corresponding to the distance from the position on the light-receiving surface where light is collected by the condenser lens to the electrode. These photocurrents Ia and Ib are generated by current-voltage conversion circuits 17a and 17.
After being converted into a voltage value by b, the amplifier circuits 18a, 18
b, and is input to the arithmetic circuit 20 as a light receiving section output. The arithmetic circuit 20 calculates the distance to the object or the moving direction of the photographing lens 26 for focusing by taking the ratio of the light receiving section outputs, and outputs the signal to the lens drive circuit 21. Arithmetic 101 path 2
The lens drive circuit 21 that received the output of 0 outputs the arithmetic circuit 20.
The output signal from the photographing lens 26 or the photographing lens 26
to adjust the focus and focus.

Next, the operation when the reflected light from the subject is weak and the S/N ratio of the input signal to the arithmetic circuit is degraded will be described.

The photocurrent output of the light receiving element 16 has a magnitude proportional to the intensity of the reflected light. That is, the output from the light receiving section is proportional to the intensity of the reflected light. The comparison circuit 19 compares the output of the light receiving section with a preset voltage value, and if the output of the light receiving section is lower, the comparison circuit 19
A pulse signal P shown in FIG. 3 is output. The pulse signal P is input to a gate circuit 14, and the gate circuit outputs a gate signal G having a pulse width τ sufficiently longer than the pulse width of the pulse signal P from when the pulse signal P is input. The gate signal G is inverted and input to the AND circuit 13, and is also input to the LED drive circuit 12b. At this time, G is turned OFF, and since the gate signal G is inverted thereafter, the LED drive circuit 12a does not receive the switch signal SW. The LED drive circuit 12b receives the gate signal G.
Then, only when the gate signal G is ON, a pulse signal L2 of a constant period shown in FIG. 3 is generated. The pulse signal L2 causes the transistor 24 in the light emitting section 8 to enter the N state, and the saturation voltage value between the emitter and collector of the transistor 24 is set to Vsat2. Assuming that the resistance value is R2, Vcc-Vsat2 I2: 1--2 A flow current 2 flows to the LEDll.

Here, if the resistance values R1 and R2 are set so that R1>R2, then E2>I1, and the amount of light emission can be switched.

The resistance value R1 is set so that the amount of light emitted by LEDll when current value 11 flows through LEDll is adapted to the situation when the subject is located at a short distance, and the current value ■2 is set as LEDl1.
If the resistance value R2 is set so that the amount of light emitted by the LED 11 when the light flows to the object is located at a long distance, the intensity of the reflected light returning to the light receiving section 10 can be maintained at a constant level. be able to.

As described above, according to this embodiment, the focus adjustment device is capable of reducing power consumption and increasing focus adjustment accuracy by switching the amount of light emitted from the light emitting section according to the output of the light receiving section. A light emission control device can be realized. Note that in the above embodiments, the light emitting element was an LED, but the light emitting element was an LED.
The light beam is not limited to D, and any light beam may be used as long as it has the function of projecting a light beam for focus adjustment. For example, a semiconductor laser can also be used.

Effects of the InventionAs is clear from the above explanation, in the present invention, the amount of light emitted from the light emitting part is switched according to the output of the light receiving part, so that the light emitting element, which normally instantaneously flows a current of several amperes, is Since the amount of current can be switched, power consumption can be significantly reduced. However, when the output of the light receiving section is small, the two light emitting sections do not need to emit light again, and the excellent effect of improving the accuracy of focus adjustment can also be obtained. Furthermore, the effect is
The output of the light receiving section approaches a certain level, the dynamic range of the intensity of the light receiving section signal is narrowed, and the subsequent signal processing circuit is simplified.

[Brief explanation of drawings]

Figure 1 is a diagram of the principle of a conventional active focus adjustment device.
FIG. 2 is a block diagram of a focus adjustment light emission control device according to an embodiment of the present invention, and FIG. 3 is a timing chart in the embodiment of FIG. 2. 1... Light emitting part, 3... Subject, 5...
... Light receiving section, 6 ... Calculation section, 7 ...
・Photographing lens drive section, 8... Light emitting section, 9...
..., drive control section, 10... light receiving section, 11.
...LED, 16... Light receiving element, 19.
... Comparison circuit, 20 ... Arithmetic circuit, 21.
...Lens drive circuit, 26...Photographing lens. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 5 6 7 2

Claims (1)

[Claims] a light emitting unit that projects a light beam for focus adjustment onto a subject; a light receiving unit that receives reflected light from the subject of the light flux for focus adjustment that is emitted from the light emitting unit and performs photoelectric conversion; and a comparison circuit that compares the output level of the controller with a certain predetermined reference level, and a signal that increases the amount of light emitted according to the output from the comparison circuit and causes the light emission to emit light again a certain number of times within a certain time. What is claimed is: 1. A light emission control device for a focus adjustment device, comprising: a drive control section that determines whether or not the light is applied to the light source.