JPS61114122A - Range measuring device - Google Patents

Abstract

PURPOSE:To prevent an error in range measurement during photography in the presence of high-brightness light such as tungsten light by shielding the nonphotodetection part of a position photodetector in a range measuring device which photodetects reflected infrared beam light from a body to be measured by the position photodetector. CONSTITUTION:A position photodetection unit 10 has a semiconductor photodetection position detecting element 11 in the center of the front surface of a frame 10a. The reflected infrared beam light projected as spot light on the element 11 varies with the distance to the subject, but even if the subject varies from short range to infinite range, there is a part where the reflected infrared beam is not projected. A light shield member 12 which is hatched is applied to the part to reduce the incidence of external light. Thus, noises in the output current of the element 11 are reduced and the possibility of an error in range measurement is reduced even in an atmosphere wherein bright external light such as tungsten light is used.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a distance measuring device that prevents erroneous distance measurement during photographing under high-intensity illumination.

(b) Prior art In recent years, autofocus cameras and autofocus video cameras have been developed, making photography much easier. A blurred image detection method that detects the sharpness of the subject image, a double image coincidence detection method that detects the overlap of the two left and right objects,
Alternatively, various methods are known, such as a top and bottom image coincidence detection method, and a ray distance method that uses the reflected light of a light beam emitted towards the object to be measured to calculate the distance by triangulation from the baseline length and viewing angle.

FIG. 2 shows the principle of distance measurement using the ray distance method, in which a narrow infrared beam is projected onto a subject 3 through a projection lens 2 from an infrared light emitting diode 1 driven by a red light control pulse. The infrared light beam reflected from the subject 3 is received as a spot light on the optical position detector 5 through the light receiving lens 4. The optical position detector 5, as shown in FIG. 3(a), is a photodiode having charging output terminals 5a, 5b and a common electrode terminal 5c connected to two electric currents [i Pl, , P2, respectively, and a common electrode terminal 5c. The position d of the infrared spot light on the detector 5 is determined by the distance from the light emitting lens 2 to the subject 3 being 1, the focal length of the light receiving lens 4 being f1, and the distance between the optical axes of the light receiving lenses 2 and 4. (called the baseline length) is S, then f d=Sx-! It can be seen that the imaging position of the infrared spot light changes as the distance to the subject 3 increases by 11 degrees. On the other hand, the photocurrent I output from the output terminals 5a and 5b of the optical position detector 5], 12
The size varies depending on the imaging position of the infrared spot light, and is expressed by the following relational expression. Here, C is the length of the light receiving surface of the optical position detector 5.

-(-'+ fs ) / (-j -fs) This relationship is illustrated in Figure 3 (b), where I2/11 is approximately 1. //It can be seen that it is proportional to f.

As can be seen from the above formula, ■2/11#, base 5is1 focal length f1 of light receiving lens 4, light receiving surface length C of optical position detector 5
Therefore, distance measurement is possible regardless of the strength of the spot light due to differences in the reflectance of the subject or deterioration of the infrared light emitting diode 1 over time. Furthermore, as can be seen from FIG. 3(b), the smaller the distance to the object, the larger the output value and the larger the change, allowing for highly accurate distance measurement.

In this way, the optical distance measurement method performs distance measurement purely electrically and does not require any mechanical mechanism or operation, making it possible to realize a compact and highly reliable distance measurement system. Since distance measurement is often carried out outdoors or under indoor lighting, it is necessary to distinguish between such extraneous light and the infrared beam light from the light emitting diode. For this reason, conventional light emitting diodes have wavelengths of 800 to 9
I use one that emits infrared rays of 50 ml and 1 m, and I also put a filter to cut visible light in front of the light receiving surface of the optical position detector, but this = 3 = It is useless against sunlight and incandescent light. Therefore, it is possible to distinguish it from external light by driving the light emitting diode in pulses or by turning it on with alternating current to extract only the change in light, or by converting the output current of the optical position detector into voltage and then processing it by logarithmically converting it. I try to avoid erroneous distance measurements by doing this.

Using this method, it is possible to distinguish between extraneous light and infrared beam light in many cases, but if the subject is illuminated with strong tungsten light, ripples may be added to the output current of the optical position detector. This may cause noise and cause incorrect distance measurement.

(c) Object and structure of the invention The present invention has been made in view of the above points, and is an object of the present invention to prevent erroneous distance measurement when photographing under high brightness lighting such as tungsten light in an automatic focusing camera or video camera. In order to achieve this goal, the optical position detector is constructed so that the non-light receiving portion is shielded from light.

) Example The present invention will be explained below based on the drawings.

FIG. 1 shows an optical position detection unit used in a distance measuring device according to the present invention.

The optical position detection unit IO includes a semiconductor device detection element 11 disposed at the center of the front surface of a frame 10a.

The reflected infrared beam light projected as a spot light onto the optical position detection element 11 changes depending on the distance to the subject, but even if the subject changes from close distance to infinity, the reflected infrared beam light is not projected on the part. There is. Therefore, by applying a light shielding member 12 as shown by diagonal lines to this portion, the incidence of external light is reduced. As the light shielding member 12, light shielding paper, light shielding paint, etc. can be considered.

In addition to providing such a light shielding member, the optical position detection element 1
Another possible method is to make the window for fixing 1 smaller.

By shielding the non-light-receiving portion of the optical position detection element in this way, the noise included in the output current of the element is reduced.
Even in an environment where bright external light such as tungsten light is used, ripples are added to the output current and the amplifier system of the output current processing circuit is less likely to be saturated, so the possibility of erroneous distance measurement is greatly reduced.

In conventional distance measuring methods, when the subject approaches infinity, the amount of received light decreases, and the output current from the optical position detection element decreases to 12
Because the distance becomes small, it is easy to mismeasure the distance. Therefore, the output current 11
．． ．． 1. , it is determined that if it falls below a certain level, it is at infinity. In the apparatus of the present invention, infinity can be reliably determined by shielding the position corresponding to infinity on the optical position detection element onto which the reflected infrared beam is projected.

(E) Effects of the Invention As explained, the present invention projects an infrared beam toward an object to be measured and receives the reflected infrared beam from the object with an optical position detector. , the rangefinder stand that measures the distance to the object based on the light receiving position is installed, and the non-light receiving part of the optical position detector is set to G to block light, so that extraneous light such as high brightness tungsten light is removed. Even when photographing in an environment of

[Brief explanation of the drawing]

FIG. 1 is a perspective view of an embodiment of the optical position detection unit used in the distance measuring device according to the present invention, FIG. 2 is a diagram explaining the principle of distance measurement, and FIG. Example, (b)
FIG. 2 is a characteristic diagram showing the relationship between the distance and output current of the optical position detector shown in FIG. l... Infrared light emitting diode 2... Light emitting lens 3... Subject 4... Light receiving lens 5... Optical position detector 10... Optical position detection unit

Claims (1)

[Claims] comprising a light projecting means for projecting a spot light onto an object to be measured, and a light receiving means disposed at a predetermined distance from the light projecting means so as to receive the spot light reflected by the object to be measured;
A distance measuring device using an optical position detector as the light receiving means, characterized in that a non-light receiving portion of a light receiving surface of the optical position detector is shielded from light.