CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a U.S. National Phase of International Patent Application Serial No. PCT/JP2019/009813 entitled “DISTANCE MEASUREMENT CAMERA,” filed on Mar. 11, 2019. International Patent Application Serial No. PCT/JP2019/009813 claims priority to Japanese Patent Application No. 2018-051643 filed on Mar. 19, 2018. The entire contents of each of the above-referenced applications are hereby incorporated by reference for all purposes.

FIELD OF THE INVENTION

The present invention generally relates to distance measuring cameras for measuring a distance to a subject, in particular to a distance measuring camera for measuring a distance to a subject based on an image magnification ratio between at least two subject images respectively formed by at least two optical systems whose changes of magnifications of the subject images according to the distance to the subject are different from each other.

BACKGROUND AND SUMMARY

In recent years, there is proposed a distance measuring camera for measuring a distance to a subject by imaging the subject. As such a distance measuring camera, there is known a stereo camera type distance measuring camera including two or more pairs of an optical system for collecting light from a subject to form a subject image and an image sensor for converting the subject image formed by the optical system to an image signal. Further, there is also known a pattern projection type distance measuring camera including a projector for projecting constant pattern light (such as grid pattern light) onto a subject and an imaging system for imaging the subject onto which the constant pattern light is being projected (for example, see patent document 1).

In the stereo camera type distance measuring camera, the two or more pairs of the optical system and the image sensor are used to obtain a plurality of images having different parallel disparities and the distance to the subject is calculated based on the parallel disparities among the plurality of obtained images. In order to accurately calculate the distance to the subject based on the parallel disparities among the plurality of images, it is necessary to obtain a large parallel disparity. Thus, it is required to arrange the two or more optical systems in one distance measuring camera with being significantly far apart from each other in a direction perpendicular to an optical axis direction thereof. This results in increase in a size of the distance measuring camera. Further, in the stereo camera type distance measuring camera, if the subject is located at a position close to the distance measuring camera, there is a case of obtaining an image in which any feature point of the subject image for obtaining the parallel disparity is shown and another image in which the same feature point of the subject image is not shown due to a relationship between fields of views of the obtained images. In order to  avoid this situation, it is necessary to arrange the two or more optical systems with being close to each other. However, when the two or more optical systems are arranged so as to be close to each other, there is a problem that the parallel disparity between the obtained images becomes small and accuracy of the measurement is decreased. Thus, there is a problem that it becomes difficult to accurately calculate the distance to the subject located at a close position with the parallel disparity among the subject images.

In the pattern projection type distance measuring camera, the constant pattern light is projected onto the subject and distortions of the constant pattern light projected onto the subject is analyzed to measure the distance to the subject. Thus, the pattern projection type distance measuring camera needs the projector for projecting the constant pattern light onto the subject. This makes a configuration of the distance measuring camera larger. Further, since the constant pattern light projected onto the subject is generally light having a wavelength outside the visible light band, the pattern projection type distance measuring camera needs a special light source. Thus, the pattern projection type distance measuring camera is not suitable to be used for normal photographing.

RELATED ART DOCUMENT

Patent Document

JP 2013-190394A

Problems To Be Solved By The Invention

The present invention has been made in view of the problems of the conventional arts mentioned above. Accordingly, it is an object of the present invention to provide a distance measuring camera which can calculate a distance to a subject without using any parallel disparities among a plurality of images and without projecting constant pattern light onto the subject.

Means For Solving The Problems

The above object is achieved by the present inventions defined in the following (1) to (9).

A distance measuring camera, comprising:

a first optical system for collecting light from a subject to form a first subject image;

a second optical system for collecting the light from the subject to form a second subject image;

an imaging part for imaging the first subject image formed by the first optical system and the second subject image formed by the second optical system; and

a distance calculating part for calculating a distance to the subject based on the first subject image and the second subject image imaged by the imaging part,

wherein the distance calculating part calculates the distance to the subject based on an image magnification ratio between a magnification of the first subject image and a magnification of the second subject image.

(2) The distance measuring camera according to the above (1), wherein the first optical system is a fixed focus optical system and the second optical system is an autofocus optical system configured so that at least one lens constituting the second optical system can be actuated.

(3) The distance measuring camera according to the above (1) or (2), wherein the first optical system and the second optical system are configured so that a change of the magnification of the first subject image according to the distance to the subject is different from a change of the magnification of the second subject image according to the distance to the subject.

(4) The distance measuring camera according to the above (3), wherein the first optical system and the second optical system are configured so that a focal length of the first optical system and a focal length of the second optical system are different from each other, and thereby the change of the magnification of the first subject image according to the distance to the subject is different from the change of the magnification of the second subject image according to the distance to the subject.

(5) The distance measuring camera according to the above (3) or (4), wherein a depth disparity in an optical axis direction exists between a front principal point of the first optical system and a front principal point of the second optical system, and thereby the change of the magnification of the first subject image according to the distance to the subject is different from the change of the magnification of the second subject image according to the distance to the subject.

(6) The distance measuring camera according to any one of the above (1) to (5), further comprising an association information storage part storing association information for associating the image magnification ratio between the magnification of the first subject image and the magnification of the second subject image with the distance to the subject,

wherein the distance calculating part calculates the distance to the subject based on the image magnification ratio between the magnification of the first subject image and the magnification of the second subject image and the association information in the association information storage part.

(7) The distance measuring camera according to any one of the above (1) to (6), wherein the distance calculating part calculates a ratio between a size of the first subject image and a size of the second subject image as the image magnification ratio between the magnification of the first subject image and the magnification of the second subject image.

(8) The distance measuring camera according to any one of the above (1) to (7), wherein the imaging part is a single image sensor for imaging both of the first subject image and the second subject image.

(9) The distance measuring camera according to the above (8), further comprising a first wavelength selection element provided on an optical path of the light for forming the first subject image to restrict a wavelength of the light forming the first subject image and a second wavelength selection element provided on an optical path of the light for forming the second subject image to restrict a wavelength of the light forming the second subject image,

wherein a wavelength band of the light forming the first subject image which is restricted by the first wavelength selection element is different from a wavelength band of the light forming the second subject image which is restricted by the second wavelength selection element.

Effect Of The Invention

The distance measuring camera of the present invention uses the two optical systems configured so that the changes of the magnifications of the subject images according to the distance to the subject are different from each other and can measure the distance to the subject based on the image magnification ratio (the ratio of the magnifications) between the two subject images respectively formed by the two optical systems. Thus, in the distance measuring camera of the present invention, it is not necessary to ensure a large parallel disparity unlike the conventional stereo camera type distance measuring camera using parallel disparities among a plurality of images. Therefore, even if the two optical systems are arranged so as to be close to each other in the parallel direction perpendicular to the optical axis direction, it is possible to accurately calculate the distance to the subject. As a result, it is possible to reduce a size of the distance measuring camera compared with the conventional stereo camera type distance measuring camera. Further, according to the present invention, it becomes unnecessary to design the distance measuring camera with considering the parallel disparities. Thus, it is possible to enhance the flexibility of design for the distance measuring camera. Furthermore, since the distance measuring camera of the present invention does not use any parallel disparity to calculate the distance to the subject, it is possible to accurately calculate the distance to the subject even if the subject is located at a position very close to the distance measuring camera.

Further, in the distance measuring camera of the present invention, it is not necessary to use a special light source such as a projector for projecting constant pattern light onto the subject unlike the conventional pattern projection type distance measuring camera. Thus, it is possible to simplify a system configuration of the distance measuring camera. As a result, it is possible to realize downsizing, weight-saving, power-saving and cost-reduction of the distance measuring camera compared with the conventional pattern projection type distance measuring camera. Furthermore, since the distance measuring camera of the present invention does not need to use any special light source for irradiating light having a wavelength outside the visible range unlike the conventional pattern projection type distance measuring camera, the distance measuring camera of the present invention can also perform normal photographing.

