JPH0534581A - Distance measuring device - Google Patents

Abstract

PURPOSE:To exactly discriminate photographing through glass and supershort distance photographing without causing the cost-up by discriminating a supershort distance and glass by whether a light receiving output level is high or low. CONSTITUTION:In the case an object to be photographed is in a supershort distance, a part of a light projecting image exists on a supershort distance detection and glass detection light receiving element 7, and since the distance is near, a current outputted from the light receiving element 7 is large. A supershort distance detection output from an output level deciding means 8 becomes an H level, and a distance determining means 10 determines that the object to be photographed exists in a supershort distance without being based on the output of a distance arithmetic means 9. In the case the object to be photographed is a distance view through glass, the greater part of light projected from a light projecting element 4 transmits through glass 6, and a part of a reflected light irradiates the light receiving element 7, therefore, light receiving power of the light receiving element 7 is small. In this case, the distance determining means 10 determines a distance for photographing a distance view without being based on the output of the distance arithmetic means 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active type distance measuring device used in an autofocus camera or the like.

[0002]

2. Description of the Related Art Conventionally, an active type distance measuring device usually has a light projecting lens 2 and a light receiving lens 3 fixed to a camera body 1 as shown in FIG.
The light projected through is reflected by the subject, and is imaged on the light receiving element 5 through the light receiving lens 3. Since the position where the image is formed on the light receiving element 5 changes according to the distance of the subject, the semiconductor position detecting device (hereinafter referred to as PSD) or the like is used to detect the light receiving position and calculate the distance.

[0003]

However, in the above conventional example, when the glass 6 is in front of the camera body 1 as shown in FIG. 6, most of the light projected from the light projecting element 4 through the light projecting lens 2 is used. Passes through the glass 6, but the light slightly diffused and reflected between the front surface (or the back surface) of the glass 6 and the camera body 1 irradiates the light receiving element 5 through the light receiving lens 3 over the entire surface. If you try to shoot a distant view from the observatory of a building or tower through a window glass, the main ray that has passed through the glass 6 does not return reflected light because the subject is a distant view, but diffuse reflected light completely covers the light receiving element 5. However, there is a drawback that an intermediate distance of, for example, 1 m to 2 m is measured, resulting in a defocused photograph.

In recent years, this problem becomes particularly noticeable due to the reduction in the distance between the light emitting and receiving lenses accompanying the miniaturization of the camera, which has been a bottleneck in downsizing the camera.

Further, a method of providing a dedicated light receiving element for receiving diffusely reflected light from the glass and discriminating whether or not the image is taken through the glass depending on the presence or absence of the output can be considered, but this causes a cost increase.

Therefore, an object of the present invention is to provide an improved distance measuring device which does not have such drawbacks, and in particular, the above-mentioned problems do not result in a significant cost increase as compared with the conventional device. It is to provide a distance measuring device that can solve the above problem.

[0007]

In the distance measuring apparatus according to the present invention, by providing a light receiving element for detecting an ultra short distance and an output level judging means for comparing the output of the light receiving element with the first level and the second level, When the level is lower than the first level, the normal distance measurement distance is selected, when the level is higher than the second level, the ultra short distance is selected, and when the level is higher than the first level and lower than the second level, the distant view shooting distance is selected.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a drawing best showing the features of the present invention. In FIG. 1, 1 to 6 are the same constituent elements as in the conventional example, and therefore their explanations are omitted. Reference numeral 7 is a light receiving element for super short distance detection and glass detection, 8 is an output level determining means for determining the output level of the light receiving element in three stages, and 9 is a known distance measuring operation means (such as Canon double integration). Is output level determination means 8
It is a distance determining means for determining the subject distance by using the output of the distance measuring calculation means 9 as an input.

FIG. 2 shows an embodiment of the output level judging means 8, 11 is an operational amplifier, and 12 is a resistor for converting the photocurrent received by the light receiving element 7 into a voltage. Reference numerals 13 and 14 are comparators, and reference numerals 15 and 16 and 17 are resistors for comparing the output voltage of the operational amplifier 11 with a value obtained by dividing the reference voltage VREF by the resistors 15, 16 and 17. Reference numerals 18 and 19 denote SR type flip-flops, which are reset by a power-up clear signal PUC from a power-on detection circuit (not shown) and set by the H-level outputs of the comparators 13 and 14, respectively, and detect the glass detection output GOUT and the super close range. The distance detection output NOUT is output.

In FIG. 3, the object distance is (A) 6.0 m,
(B) 1.2 m, (C) 0.6 m, (D) 0.4 m,
(E) Images 20A, 20B, 2 of the light projecting element 4 formed on the light receiving element 5 and the light receiving element 7 in the case of 0.2 m
0C, 20D, and 20E are shown. (A) to (E)
As the distance becomes shorter, the center of the light projecting element 4 moves and the focused image becomes larger at 1.2 m.
Here, the normal distance measuring range is 6.0 m to 0.6 m, the image is almost in the light receiving element 5, and there is linearity in the change of the output with respect to the change of the distance. At 0.4 m of (D), the image 20D straddles the light receiving element 5 and the light receiving element 7, and the center is deviated from the light receiving element 5, so there is no linearity in the output change with respect to the change in distance. Further, the proportion of the image on the light receiving element 7 is small, but the light receiving power is large because the distance is short. At 0.2 m of (E), the image 20E does not exist on the light receiving element 5 and becomes large due to blurring. Therefore, about 1/4 to 1/5 of the image is formed on the light receiving element 7, The power is great.

The operation of the above configuration will be described with reference to the flowchart of FIG.

When the power is turned on in # 1, the power-up clear signal PUS is output and the flip-flops 18 and 19 are reset, so that the outputs GOUT and NOUT are at the L level (# 2).

At # 3, the light projecting by the light projecting element 4 is started.

The subject is a normal distance measuring range (6 m to 0.6 m)
In the case of , the light receiving output by the projected images 20A, 20B, 20C formed on the light receiving element 5 is calculated by the distance calculating means 9 as shown in FIGS. The information is input to the distance determining means 10. Further, since the projected images 20A, 20B, 20C are not formed on the light receiving element 7, the output of the operational amplifier 11 of the output level determination means 8 becomes the same voltage as the reference voltage VREF, and the outputs of the comparators 13 and 14 are both L. GOUT and NO at the level
Since the UT is also at the L level, the distance determining means 10 determines the distance from the output of the distance calculating means 9 like # 6 via # 4, # 5.

The subject is a very short distance (0.4 m to 0.2 m)
In such a case, as shown in FIG. 3D, part of the projected image 20D is the light receiving element 5
When it is above, the distance information calculated by the distance calculation means 9 is closer than 0.6 m but farther than 0.4 m. The movement of the center of gravity on the light receiving element 5 is small relative to the movement of the center of gravity of the image.

Further, when the projected image 20E is not on the light receiving element as shown in FIG. 3 (E), there is no signal to enter the calculating means 9, so that distance information of infinity appears. On the other hand, there is a part of the projected image 20D or 20E on the light receiving element 7 in both cases (D) and (E) of FIG. 3, and since the distance is short, the current output from the light receiving element is large, Operational amplifier 1
The output voltage of 1 becomes a voltage low enough to bring the output of the comparator 14 to the H level, the flip-flop 19 is set, and the super short distance detection output NOUT also becomes the H level, so that the distance like # 7 is passed through # 4. It is determined that there is a subject at a very short distance regardless of the output of the calculation means 9.

In the case where the object is a distant view through glass, in this case, the light diffusely reflected by the glass 6 and the camera body 1 illuminates the entire surface of the light receiving elements 5 and 7. Therefore, since the center of the light incident on the light receiving element 5 is substantially the center of the light receiving element 5, the distance information calculated by the distance calculating means 9 is about 1.2 m. Further, most of the light projected from the light projecting element 4 passes through the glass 6 and a part of the reflected light irradiates the light receiving element 7, so that the light receiving power of the light receiving element 7 is small. Therefore, the operational amplifier 11
Output voltage of the comparator 13 is set to the H level, but the output of the comparator 14 remains at the L level, only the flip-flop 18 is set, and only the glass detection output GOUT becomes the H level. Like # 8 via # 4 and # 5, the distance determining means 10 determines the distance for long-distance shooting such as infinity or the hyperfocal distance of the taking lens, regardless of the output of the distance calculating means 9.

In the above embodiment, the glass detection and the ultra short distance detection are performed by the two comparators, but most of the glass detection is transmitted through the glass and slightly reflected light as compared with the super short distance received light output. Since only the light can be received, it is preferable to directly detect only the ultra-short distance by the comparator and integrate the glass detection.

The input to the distance measuring calculation means is switched to input the normal distance measuring light receiving element and the glass detecting light receiving element to the distance measuring calculation means in a time-sharing manner so that the output level determining means and the distance measuring calculation means can also be used. Is also good.

[0020]

As described above, according to the distance measuring apparatus of the present invention, the light receiving element for detecting the ultra-short distance and the light receiving element for detecting the glass are used in combination, so that the light receiving output level is large and the distance between the ultra-short distance and the glass is large. By distinguishing between, it is possible to shoot a distant view through the glass with almost no increase in cost.

[Brief description of drawings]

FIG. 1 is a block diagram of a camera embodying the present invention.

FIG. 2 is a circuit diagram of an embodiment of the output level determining means shown in FIG.

FIG. 3 is a diagram showing image formation reflected light on a light receiving element depending on a subject distance.

FIG. 4 is an operation flowchart of the present invention.

FIG. 5 is a configuration diagram of a light emitting / receiving optical system of a distance measuring device of a camera.

FIG. 6 is an optical path diagram of unnecessary reflected light when photographing through glass.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Camera main body 2 ... Emitting lens 3 ... Light receiving lens 4 ... Emitting element 5 ... Normal distance measuring light receiving element 6 ... Glass 7 ... Ultra short distance detection and glass detecting light receiving element 8 ... Output level determination means 9 ... Distance Computing means 10 ... Distance determining means

Claims (1)

Claim: What is claimed is: 1. An active-type distance measuring apparatus having a light-receiving element for detecting an ultra-short distance, wherein an output level determination is made by comparing the output of the light-receiving element with a first level and a second level. A distance measuring device comprising means.