JPH09189941A - Range finder for camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a range finder capable of maintaining high range finding accuracy at a telephoto time while covering a sufficient range finding extent at a wide photo time in order to attain multipoint range finding, and also not checking the camera from being made compact. SOLUTION: The range finder is provided with a pair of short focus image forming lenses 21a and 21b having a wide range finding extent suitable to the multipoint range finding at the wide photo time and a pair of long focus image forming lenses 23a and 23b having a narrow range finding extent capable of maintaining the high range finding accuracy at the telephoto time. And by switching movable mirrors 22a and 22b, a luminous flux transnmitted through either short, or long focus image forming lens is selectively made incident on CCD line sensors 30a and 30b so as to obtain an object distance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a passive distance measuring device for measuring a subject distance by using an imaging lens system provided separately from a taking lens.

[0002]

2. Description of the Related Art A distance measuring device of this type has been conventionally mounted on a so-called compact type lens shutter camera. As shown in FIG. 5, the distance measuring device is arranged at a rear side of a pair of imaging lenses 1 and 2 for taking in subject light, and is incident via the imaging lens 1 or 2 respectively. A pair of line sensors 3, which receive the light flux
And 4.

The image forming lenses 1 and 2 are provided in parallel on the camera body so that their optical axes are parallel to each other. The distance between these optical axes is the baseline length B, the distance from the principal point position of each imaging lens to the line sensor along the optical axis is the imaging distance F, and the distance from the lens principal point to the subject is the subject distance L. .

By comparing the outputs of the line sensors 3 and 4, the finite image forming interval X, which is the interval between the points where the light beam from the subject reaches on the line sensor, and the interval between the points where the light beam from infinity reaches. Infinite image formation interval B (equal to baseline length)
The difference Δ = X−B can be obtained, and the subject distance L can be obtained by L = B · F / Δ based on the difference Δ and the known amounts B and F.

Further, by dividing the area of each line sensor into a plurality of areas and comparing the outputs of the corresponding portions, the distances of a plurality of objects can be detected independently (multipoint distance measurement).

It should be noted that Δ with respect to the unit change amount of the subject distance
The larger the change in the base line length B and the image forming distance F, the greater the change amount in. However, in order to make the camera compact, it is required that the distance measuring device itself is also compact. Therefore, from the viewpoint of compactness, it is more desirable that both the base line length and the imaging distance be smaller.

[0007]

However, in the above-described conventional distance measuring device, if the main purpose is to realize multi-point distance measuring at wide time, the distance measuring accuracy at tele time becomes insufficient, and conversely at tele time. If the focal length F of the image forming lens is increased in order to secure the distance measurement accuracy in (1), the range in wide angle is narrowed and it becomes difficult to perform multipoint distance measurement.

Further, in order to satisfy both the multi-point distance measurement at wide time and the distance measurement accuracy at tele time, the focal length F
It is necessary to increase both the line length and the base line length B, and also to increase the size of the line sensor. In this case, however, there is a problem that the distance measuring device becomes large and the camera cannot be made compact.

The present invention has been made in view of the above-mentioned problems of the prior art, and covers a range sufficient for realizing multi-point range measurement at wide range, and at the same time improves range-finding accuracy at tele time. An object of the present invention is to provide a distance measuring device that can be kept high and that does not hinder the downsizing of a camera.

[0010]

In order to achieve the above object, a distance measuring device according to the present invention has a pair of first focal lengths having a wide distance measuring range suitable for multi-point distance measurement at wide angle. A lens is provided, and a pair of lenses having a second focal length with a narrow range capable of maintaining high distance measurement accuracy at the time of telephoto are provided outside with a lens having a first focal length interposed therebetween. The light receiving element is arranged on the optical axis of the lens having the first focal length, and an optical path changing means is provided for guiding the light beam incident through the lens having the second focal length to the light receiving element. A switching means for selectively allowing the light flux incident through the lens having the focal length and the light flux incident through the lens having the second focal length to enter the light receiving element, and Find the subject distance based on the output Characterized in that a computing means.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a distance measuring device according to the present invention will be described below. FIG. 1 is an explanatory diagram showing a basic configuration of an optical system and a control system showing a first embodiment of the present invention.

This distance measuring device comprises a pair of short focus image forming lenses 21a and 21b having a first focal length arranged in parallel so as to form an image of light from the subject side, and a short focus image forming lens. And the CCD line sensors 30a and 30b, which are a pair of light receiving elements, which are arranged on the optical axis and receive the light flux from the subject side incident through the short focus imaging lens.

Outside the short-focus image forming lenses 21a and 21b, there is a second focal length different from those of the short-focus image forming lenses 21a and 21b, and a pair of long images are formed to form light from the subject side, respectively. Focus imaging lenses 23a and 23b are arranged. The short focus image forming lenses 21a and 21b and the long focus image forming lenses 23a and 23b are such that the optical axes of the respective lenses indicated by the alternate long and short dash lines are parallel to each other and all the optical axes are included in the same plane. It is arranged.

The light flux transmitted through the long-focus imaging lenses 23a and 23b is a pair of fixed mirrors 24 which are optical path deflecting means.
The light is reflected inward by a and 24b toward the optical axis side of the short focus imaging lens. In the optical paths of the light beams reflected by these fixed mirrors 24a and 24b, the movable mirror 22
a and 22b are located. Movable mirrors 22a, 22b
Has a mirror surface at least on the side facing the fixed mirrors 24a and 24b. Each movable mirror 22
The a and 22b are driven by the solenoids 31a and 31b and are rotatable between a first position shown by a solid line and a second position shown by a broken line.

When the movable mirrors 22a and 22b are set to the first position indicated by the solid line, the light flux (solid line) incident through the short focus image forming lenses 21a and 21b enters the CCD line sensors 30a and 30b. The light enters through the long-focus imaging lenses 23a, 23b and enters the fixed mirrors 24a, 2
The light beam (broken line) reflected by 4b is moved by the movable mirrors 22a, 22a.
CCD line sensors 30a, 30b blocked by b
Does not reach.

On the other hand, when the movable mirrors 22a and 22b are set to the second position shown by the broken line, the light flux (broken line) incident through the long-focus imaging lenses 23a and 23b is fixed mirrors 24a and 24b. , The light beams (solid lines) that are sequentially reflected by the movable mirrors 22a and 22b and are incident on the CCD line sensors 30a and 30b, and that are incident through the short focus imaging lenses 21a and 21b are blocked by the movable mirrors 22a and 22b, and the CCD lines are displayed. It does not reach the sensors 30a, 30b.

The output signals of the CCD line sensors 30a and 30b are input to a distance measuring circuit 32 which is a calculating means, and a subject distance is calculated. In this example, in order to realize multi-point distance measurement, the distance measuring circuit 32 divides the outputs of the pair of CCD line sensors 30a and 30b into a plurality of areas, respectively, and compares the outputs of the corresponding areas. , Object distances are obtained for a plurality of regions.

Since the distance between each imaging lens and the CCD line sensor is fixed, a sharp image is not always formed on the line sensor, but the distance measuring circuit 32 is not formed.
If the image on the line sensor has a predetermined contrast, the object distance can be calculated even if the image is out of focus.

The focus drive mechanism 33 controls the photographing lens 11 so that a focused object image is formed on the film surface 16 in accordance with the distance of the object having the shortest distance among the plurality of objects whose distances have been detected. To drive. Further, the focal length of the taking lens 11 is detected by the focal length detection circuit 34 based on a signal from an input means such as a zoom code plate, and the mirror switching circuit 35 is solenoids 31a, 31b according to the detected focal length. Is controlled so that the luminous flux incident through the short-focus imaging lenses 21a and 21b and the luminous flux incident through the long-focus imaging lenses 23a and 23b are selectively incident on the CCD line sensors 30a and 30b.

FIG. 2 shows the relationship between the photographing range and the distance measuring range when the respective image forming lenses are used, separately for the tele time and the wide time. A rectangle shown by a solid line in the drawing shows a photographing range imprinted on the film surface, and a rectangle shown by a broken line shows a distance measuring range detected by the CCD line sensor. The distance measuring range can be considered as a range in which the light receiving area of the CCD line sensor is projected through the imaging lens, that is, a range conjugate with the light receiving area. A circle indicated by a broken line in the distance measuring range indicates an approximate range of a subject as a distance measuring target in multi-point distance measuring. Distances are measured for objects at these locations within the shadow range.

FIGS. 2A and 2B show a short focus image forming lens 21.
The relationship between the photographing range and the distance measuring range when a and 21b are used is shown. The short-focus imaging lenses 21a and 21b have a relatively short base line length B and an imaging distance F (see FIG. 5). Therefore, when using a light flux incident through these lenses, a wide range is used. Although it can cover as a distance measurement target,
The ranging accuracy is low. Therefore, at the wide time shown in FIG. 2 (A), an appropriate distance measuring range can be obtained, and
Even in the case of multi-point distance measurement, a subject at a sufficiently distant position can be set as an independent distance measurement target. However, at the time of telephoto shown in FIG. Become.

On the tele side with a large focal length, it is necessary to drive the lens with higher precision than on the wide side, so it is desirable to detect the subject distance with higher precision. However, the state shown in FIG. In that case, sufficient distance measurement accuracy cannot be obtained.

2C and 2D show the long-focus imaging lens 23.
The relationship between the photographing range and the distance measuring range when a and 23b are used is shown. The long focus imaging lens has a base length B and an imaging distance F.
Since both are relatively long, when using a light flux incident through these lenses, a high ranging accuracy can be secured although the ranging range is narrowed. Therefore, at the time of telephoto shown in FIG. 2C, it is possible to obtain a distance measuring range having an appropriate width and to maintain high distance measuring accuracy. However, in the wide range shown in (D), the distance measuring range becomes too small to target a sufficiently distant subject, which makes it practically difficult to realize multipoint distance measuring.

In the distance measuring device of FIG. 1, the focal length detecting circuit 3
Based on the output of No. 4, when the focal length of the taking lens 11 is set to the wide side, the mirror switching circuit 35 sets the movable mirrors 22a and 22b to the first position shown by the solid line so that the solenoid 31a, 31b is controlled so that the luminous flux incident through the short-focus imaging lenses 21a and 21b is C
It is incident on the CD line sensors 30a and 30b.

Further, when the focal length of the taking lens 11 is set to the tele side, the movable mirrors 22a and 22b.
Is set to the second position indicated by the broken line, and the light flux that enters through the long-focus imaging lenses 23a and 23b enters the CCD line sensors 30a and 30b.

As a result, the state of (A) and the state of (C) of FIG. 2 can be switched and used, and (B) and (D) of FIG.
It is possible to take advantage of only the characteristics of the respective imaging lenses without falling into the state shown in FIG.

Further, although the size of the optical system of the distance measuring device in the width direction perpendicular to the optical axis is larger than that of the conventional example of the two lenses, the optical path on the side of the long focus imaging lens is bent by a mirror so that the optical axis direction is increased. The size in can be kept small. Generally, the size of the camera is small in the optical axis direction and large in the width direction perpendicular to the optical axis direction. Therefore, it is important to suppress the size in the optical axis direction at least in order to prevent the camera from becoming large.

FIG. 3 is a perspective view showing the appearance of a camera 10 provided with the distance measuring device of FIG. On the front surface of the camera 10 provided with the photographing lens 11, adjacent to the finder window 12, short focus image forming lenses 21a and 21b and long focus image forming lenses 23a and 23b of the distance measuring device are arranged.

Reference numeral 13 in FIG. 3 indicates a viewfinder opening and 1
Reference numeral 4 is a shutter button, and 15 is a zoom lever. The camera 10 of the embodiment is configured such that the focal length of the taking lens 11 is changed by operating the zoom lever 6 and the magnification of the finder is also changed according to the change.

FIG. 4 shows a second distance measuring device according to the present invention.
It is explanatory drawing of the optical system which shows embodiment. The control system is the same as that of the first embodiment shown in FIG.

In this example, instead of the movable mirror of the embodiment shown in FIG. 1, half mirrors 25a and 25b are short focus imaging lenses 21a and 21b and CCD line sensor 30a.
It is arranged between 30b and 30b.

The half mirrors 25a and 25b allow a part of the light flux incident through the short focus imaging lenses 21a and 21b to pass through and enter the CCD line sensors 30a and 30b, and are reflected by the fixed mirrors 24a and 24b. A part of the luminous flux incident via the long-focus imaging lenses 23a and 23b is reflected and incident on the CCD line sensor.

In the space between the lens and the mirror,
A slidable light shielding plate 26a, 2 is provided as a shutter for selectively blocking either the light beam entering through the short focus image forming lens or the light beam entering through the long focus image forming lens.
6b are arranged.

The light blocking plates 26a and 26b are driven by drive motors 36a and 36b controlled by a switching means similar to the mirror switching circuit shown in FIG. 1, and selectively block the optical path at the rear stage of the lens. As the shutter, in addition to the mechanically movable light-shielding plate shown in this example,
It is also possible to use means without mechanical actuation parts, such as liquid crystal shutters.

In the range finder of FIG. 4, when the focal length of the taking lens 11 is set to the wide side, the light shielding plate 2
The drive motors 36a and 36b are controlled so as to set the 6a and 26b to the first positions indicated by the solid lines, and the luminous fluxes that have entered through the short focus imaging lenses 21a and 21b are made to enter the CCD line sensors 30a and 30b.

On the other hand, when the focal length of the taking lens 11 is set to the tele side, the drive motor 36 is set so as to set the light shielding plates 26a and 26b to the second position shown by the broken line.
a and 36b are controlled, and the long-focus imaging lenses 23a and 23
The light flux incident via b is the CCD line sensor 30a,
It is incident on 30b.

[0037]

As described above, according to the distance measuring device of the present invention, by using two sets of lenses having different focal lengths properly, a distance measuring range sufficient to realize multi-point distance measurement at wide range is achieved. It is possible to maintain high range-finding accuracy at the time of telephoto while also covering the above, and to avoid increasing the size of the camera.

Therefore, by selecting which of the image forming lenses the light flux transmitted through is used according to the focal length of the photographing lens, a wide distance measuring range sufficient for multi-point distance measurement can be ensured at wide range, and In telephoto mode, it is possible to perform highly accurate distance measurement by increasing both the base line length and the image formation distance.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an optical system and a control system of a distance measuring device according to a first embodiment.

FIG. 2 is an explanatory diagram showing a relationship between a photographing range and a distance measuring range when the apparatus of FIG. 1 is used.

FIG. 3 is a perspective view showing the external appearance of a camera incorporating the device of FIG.

FIG. 4 is an explanatory diagram showing an optical system of a distance measuring device according to a second embodiment.

FIG. 5 is an explanatory diagram showing the principle of a passive distance measuring device.

[Explanation of symbols]

 21a, 21b Short-focus imaging lens 22a, 22b Movable mirror 23a, 23b Long-focus imaging lens 24a, 24b Fixed mirror 30a, 30b CCD line sensor 31a, 31b Solenoid 32 Distance measuring circuit 33 Focus drive mechanism 34 Focal distance detection circuit 35 Mirror switching circuit

Claims (8)

[Claims] 1. A pair of lenses having a first focal length, which are arranged in parallel so as to form images of light from the subject side, respectively, and a lens having the first focal length, which is arranged on the optical axis. ,
A pair of light receiving elements for receiving a light flux from the subject side incident through the lens having the first focal length, and a second focal length different from the first focal length,
A pair of lenses having the first focal length are sandwiched between the pair of lenses so that light from the subject side is imaged respectively.
A pair of lenses arranged one by one, an optical path deflecting means for guiding a light beam incident through the pair of lenses having the second focal length to the pair of light receiving elements, and a lens having the first focal length Switching means for selectively allowing the light beam incident via the lens and the light beam incident via the lens having the second focal length to enter the light receiving element, and the subject distance based on the outputs of the pair of light receiving elements. A distance measuring device for a camera, comprising: 2. The lens having the first focal length and the lens having the second focal length have optical axes parallel to each other and all optical axes are in the same plane. The distance measuring device for a camera according to claim 1, wherein the distance measuring device is arranged so as to be included in the camera. 3. The pair of fixed mirrors for reflecting the light flux incident through the pair of lenses having the second focal length toward the optical axis of the lens having the first focal length. , Is provided so as to be insertable into and removable from the optical path of a light beam incident through the lens having the first focal length, and is incident through the lens having the first focal length when inserted into the optical path. And a pair of movable mirrors that reflect the light beam deflected by the fixed mirror to the light receiving element side, and the switching means switches between insertion and removal of the movable mirror in the optical path. The distance measuring device for a camera according to claim 1, wherein the distance measuring device is a camera. 4. The optical path deflecting means includes a pair of fixed mirrors for reflecting a light beam incident through the pair of lenses having the second focal length to the optical axis side of the lens having the first focal length. , A pair of a part that transmits a part of the light beam incident through the lens having the first focal length to the light receiving element side and reflects a part of the light beam deflected by the fixed mirror to the light receiving element side. A half mirror, and the switching means selectively selects one of a light beam incident through the lens having the first focal length and a light beam incident through the lens having the second focal length. A shutter for shutting off the light is provided.
A distance measuring device for a camera according to any one of 1. 5. The distance measuring apparatus for a camera according to claim 1, wherein the switching means selects a light beam incident on the light receiving element according to a focal length of a photographing lens of the camera. apparatus. 6. The switching means causes a light flux incident through the lens having the first focal length to enter the light receiving element when the focal length of the photographing lens is short, and the focal length of the photographing lens is The distance measuring device for a camera according to claim 5, wherein a light flux that is incident through the lens having the second focal length when it is long is incident on the light receiving element. 7. The calculating means calculates object distances for a plurality of objects by dividing outputs of the pair of light receiving elements into a plurality of areas and comparing outputs of corresponding areas. The distance measuring device for a camera according to any one of claims 1 to 6. 8. The distance measuring device for a camera according to claim 1, wherein the first focal length is longer than the second focal length.