JP2003167195A - Optical device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical device capable of receiving an image in a wide area with less distortion. <P>SOLUTION: The optical device 10 is provided with a lens 14, an image receiving surface 18 for receiving an optical image transmitted through the lens, a 1st reflection mirror 22 arranged around the lens by taking the optical axis 12 of the lens as a center, and a 2nd reflection mirror 26 for reflecting the light reflected by the 1st reflection mirror toward the lens, the reflection surfaces 24 and 28 of the 1st and 2nd reflection mirrors are formed so that the optical image enlargement ratio at the center part of the image receiving surface may become larger or smaller than the optical image enlargement ratio at the peripheral part of the image receiving surface. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical device, and more particularly to an optical device used to capture a light image with a wide field of view.

[0002]

2. Description of the Related Art A fisheye lens is used to image or monitor a very wide range with a single camera, and most of the fisheye lenses currently offered are equidistant projection methods (Ogura Toshifu, 1995, Asahi). Sonorama issue)) has been adopted.

[0003]

However, when a surveillance camera equipped with a fisheye lens adopting the equidistant projection method is mounted downward on the ceiling to monitor the entire room, the subject directly under the camera appears large, but However, there is a problem that the image becomes smaller as it goes away from directly under the camera, and the distortion of the captured image becomes large.

Further, when a camera equipped with a fisheye lens is used to inspect the inner wall of a conduit such as a water pipe, if the optical axis of the camera is inserted along the conduit, the inner wall part right next to the camera is largely reflected, There was a problem that the inner wall part in the remote place looks small.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and an optical device includes a lens, an image receiving surface for receiving an optical image transmitted through the lens, and a first reflection member. A mirror and a second reflecting mirror that reflects the light reflected by the first reflecting mirror toward the lens, and the reflecting surfaces of the first reflecting mirror and the second reflecting mirror are the light at the center of the image receiving surface. It is characterized in that it is formed in a shape such that the image enlargement ratio is larger than the optical image enlargement ratio in the peripheral portion of the image receiving surface.

Another form of this optical device is characterized in that the reflecting surfaces of the first reflecting mirror and the second reflecting mirror are formed so as to satisfy the following relationship.

In another optical device of the present invention, a lens, an image receiving surface for receiving an optical image transmitted through the lens, a first reflecting mirror, and the light reflected by the first reflecting mirror are reflected toward the lens. And a second reflecting mirror for controlling the reflecting surface of the first reflecting mirror and the reflecting surface of the second reflecting mirror, wherein the optical image magnification at the central portion of the image receiving surface is smaller than that at the peripheral portion of the image receiving surface. It is characterized in that it is formed in. Optical device.

Another form of this optical device is characterized in that the reflecting surfaces of the first reflecting mirror and the second reflecting mirror are formed so as to satisfy the following relationship.

In another form of the above-mentioned optical device, the second reflecting surface has an opening centered on the optical axis, and the second reflecting surface has a second opening.
The lens is arranged.

Another form of the above-mentioned optical device is the first
The lens and the second lens are covered with a transparent cover having a substantially hemispherical shape or a substantially dome shape symmetrical with respect to the optical axis.

Another optical device of the present invention has an optical system including a lens or a reflecting mirror, and an image receiving surface for receiving the light guided by the optical system, and the optical system is an optical image at the center of the image receiving surface. It is characterized in that the magnification is designed to be larger than the optical image magnification in the peripheral portion of the image receiving surface.

Further, another optical device of the present invention has an optical system including a lens or a reflecting mirror and an image receiving surface for receiving the light guided by the optical system, and the optical system has a central portion of the image receiving surface. It is characterized in that the optical image magnification is designed to be smaller than the optical image magnification in the peripheral portion of the image receiving surface.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A plurality of embodiments of the present invention will be described below with reference to the accompanying drawings. In the following description, in order to facilitate understanding, terms indicating various directions (for example, “up”, “down”, “right”, “left”, “rear”,
“Before” and terms including these are used, but the present invention is not limited to these terms. Further, in the following description, the “lens” includes not only a lens formed by one lens but also a combined lens formed by a plurality of lenses.

[First Embodiment] FIG. 1 shows a surveillance camera 10 embodying an optical device according to a first embodiment. The surveillance camera 10 includes a lens (imaging lens) 14 having an optical axis 12 oriented in the vertical direction of the drawing. Lens 1
An image pickup device 16 is arranged under the lens 4
The optical image formed by is received by the image receiving surface 18 of the image pickup device 16. On the lens 14, a symmetrical semispherical or dome-shaped transparent cover 20 having a symmetrical shape about the optical axis 12 is arranged. A donut-shaped main mirror (first reflecting mirror) 22 centered on the optical axis 12 is arranged inside the transparent cover 20 and outside the lens 14. Reflecting surface (first reflecting surface) that is the upper surface of the primary mirror 22.
24 is processed to have a convex shape facing upward, as clearly shown in the portion shown by the cross section in FIG.
A sub-mirror (first reflecting mirror) 26 is arranged inside the transparent cover 20 and directly above the lens 14. The reflection surface (second reflection surface) 28, which is the lower surface of the secondary mirror 26, has a downwardly convex shape (for example, a conical shape), as clearly shown in the portion represented by the cross section in FIG. Has been processed into. According to the surveillance camera 10 configured in this way, as shown in the figure, the light 30 entering the primary mirror 22 among the lights entering the surveillance camera 10 is reflected by the reflecting surface 2 of the primary mirror 22.
4 and then the reflecting surface 28 of the secondary mirror 26, and the image is formed on the image receiving surface 18 of the image pickup device 16 by the lens 14.

The shapes of the reflecting surfaces 24 and 28 of the primary mirror 22 and the secondary mirror 26 will be described. For ease of understanding, FIG.
As shown in, consider a case where the viewing angle of the surveillance camera 10 is 180 ° and the hemispherical virtual surface 32 of the diameter d is photographed from the surveillance camera 10. In this case, assuming that the direction of the optical axis 12 is the direction of the incident angle 0, the incident angle φ is centered on the optical axis 12.
Circumference c _phi circle 34 on the hemisphere imaginary surface 32 which is visible in the direction of
Is given by equation (1).

The perimeter c _max of the circle 36 on the virtual surface 32 of the hemisphere, which is visible in the direction of the incident angle of 90 °, is given by the equation (2).

Here, since the prospective angle of the circle 36 on the hemispherical virtual surface 32 seen in the incident angle 90 ° direction as viewed from the surveillance camera 10 is 2π, the circle 34 on the hemispherical virtual surface 32 seen in the incident angle φ direction. The angle of view of is given by equation (3).

Next, let us consider a case where a circular image 38 having a radius of 1 appears on the image receiving surface 18 of the image pickup device 16 as shown in FIG. In this case, the circumferential length _{c y} of a circle 40 of radius y is given by Equation (4).

Further, this circle 40 is a circle 34 on the virtual surface 32 of the hemisphere which is seen from the surveillance camera 10 in the direction of the incident angle φ.
If the image is completely overlapped with, the relationship of Expression (5) is established.

By modifying the equation (5), the equation (6) is obtained.

Integrating equation (6) yields equation (7).

Here, when φ = 0, y = 0. Therefore, C = 0. Therefore, Equation (8) is derived from Equation (7).

When the relation of the expression (8) is established, as shown in FIG. 4, in the light image 42 of the image receiving surface 18 on which the small spherical object on the virtual hemispherical surface 32 is projected, the diameter around the optical axis 12 is the center. The width AB in the direction and the width CD in the circumferential direction are equal. Also, from equation (5), when φ = 0 and y = 0, When φ = π / 2 and y = 1, Therefore, the optical image with the incident angle of 90 ° is received with a magnification of 2 times that of the optical image with the incident angle of 0 °. Therefore, as shown in FIG. 5, even if the incident angle is changed and a minute sphere is imaged, the optical image 44 of the sphere does not distort and only the size changes.

From the above, the reflecting surfaces 2 of the primary mirror 22 and the secondary mirror 26
By designing 4 and 28 so as to satisfy the relationship of the expression (8), the image around the image receiving surface is enlarged and displayed compared to the image at the center of the image receiving surface. Therefore, for example, when the surveillance camera 10 is mounted downward on the ceiling to monitor the entire room, the subject is separated from the surveillance camera 10 as it is farther away from directly below the surveillance camera 10 (that is, closer to the periphery of the image receiving surface). Although the angle of view becomes smaller as the distance increases, the image taken does not become smaller as the magnification increases, and the subject can be easily monitored.

[Embodiment 2] When a surveillance camera equipped with a fisheye lens is used to inspect the inner wall of a pipeline such as a water pipe, when the optical axis of the camera is inserted along the pipeline, the inner wall portion right next to the camera is It looks large, but the inner wall part at a distance in front looks small. Therefore, contrary to the design of the primary mirror 22 and the secondary mirror 26 for the surveillance camera 10 of the first embodiment, the reflecting surfaces 24 and 28 of the primary mirror 22 and the secondary mirror 26 are expressed by the formula (9).
To satisfy the relationship

According to the surveillance camera thus designed, the image of the central portion of the image receiving surface is enlarged and displayed compared to the image of the peripheral portion of the image receiving surface. If the optical axis of is inserted parallel to the rotational symmetry axis (long axis) of the water pipe, the inner wall part in front of the camera (that is, closer to the center of the image receiving surface) will make the subject farther from the surveillance camera. Although the angle becomes smaller, the image taken does not become smaller as the magnification increases, and the inner wall of the water pipe can be easily inspected.

[Third Embodiment] A first embodiment shown in FIG.
As shown in FIG. 6, in the surveillance camera 10 of FIG. 6, the blind spot is behind the secondary mirror 26 in the field of view 46, and the light traveling from behind the secondary mirror 26 toward the secondary mirror 26 is blocked by the secondary mirror 26. , Does not enter the lens 14. Therefore, as shown in FIG. 7, a circular opening 50 having the optical axis 12 as the center is formed in the center of the secondary mirror 26, and a lens (for example, a concave lens) 52 is arranged in the opening 50, and It is desirable that the light traveling from the front toward the lens 14 is condensed by the lens 52 and is incident on the lens 14. As a result, the field of view 46 of the surveillance camera 10 is expanded, and a wide range of subjects can be imaged.

[Fourth Embodiment] The present invention can be applied to a lens or a lens system which does not include a reflecting mirror. Specifically, as shown in FIG. 8, in the lens system (combined lens) 54 composed of a plurality of lenses, the lens system 5
The lens system 54 is designed so as to satisfy Expression (10), where φ is the incident angle of the light incident on 4, the image height on the image receiving surface 18 is Y, and the maximum value of the image height is Y _max. ,
The enlargement ratio of the peripheral portion of the image receiving surface can be made larger than that of the central portion of the image receiving surface.

As a result, for example, when the surveillance camera 10 is mounted downward on the ceiling to monitor the entire room, the further the subject is from directly under the surveillance camera 10 (that is, the closer to the periphery of the image receiving surface), the more the subject becomes. Although the perspective angle becomes smaller as the distance from the surveillance camera 10 increases, the image taken by the enlargement ratio does not become smaller and the subject can be easily monitored.

On the contrary, by designing the lens system 54 so as to satisfy the expression (11), it is possible to increase the enlargement ratio of the central portion of the image receiving surface as compared with the peripheral portion of the image receiving surface.

As a result, the image of the central portion of the image receiving surface is enlarged compared to the image of the peripheral portion of the image receiving surface. For example, when used for inspection of the inner wall of a water pipe, the optical axis of the camera is rotationally symmetrical with respect to the water pipe. Inserted parallel to the axis (major axis), the inner wall part in front of the camera (that is, closer to the center of the image receiving surface)
The farther the subject is from the surveillance camera, the smaller the angle of view becomes, but the image taken does not become smaller as the magnification increases, and the inner wall of the water pipe can be easily inspected.

[0032]

As is apparent from the above description, according to the optical device of the present invention, it is possible to receive an image of a wide area with little distortion.

[Brief description of drawings]

FIG. 1 is a perspective view showing a first embodiment of an optical device according to the present invention.

FIG. 2 is a perspective view showing a spherical virtual surface centered on the optical device shown in FIG.

FIG. 3 is a plan view showing a circular image received on an image receiving surface.

FIG. 4 is a plan view showing an image of a spherical subject which is received on the image receiving surface.

FIG. 5 is a plan view showing a state in which spherical objects of the same size are received on the image receiving surface.

FIG. 6 is a cross-sectional view showing an optical path blocked by a secondary mirror in the first embodiment.

FIG. 7 is a sectional view of the optical device according to the third embodiment.

FIG. 8 is a sectional view of the optical device according to the fourth embodiment.

[Explanation of symbols]

10 surveillance camera, 12 optical axis, 14 lens, 16
Imaging device, 18 image receiving surface, 20 transparent cover, 22 primary mirror, 24 reflective surface, 26 secondary mirror, 28 reflective surface, 30
light.

Claims (8)

[Claims] 1. A lens, an image receiving surface for receiving an optical image transmitted through the lens, a first reflecting mirror, and a second reflecting mirror for reflecting the light reflected by the first reflecting mirror toward the lens. And the reflecting surfaces of the first reflecting mirror and the second reflecting mirror are formed in a shape such that the optical image magnification at the central portion of the image receiving surface is larger than the optical image magnification at the peripheral portion of the image receiving surface. Characterized optical device. 2. The optical device according to claim 1, wherein the reflecting surfaces of the first reflecting mirror and the second reflecting mirror are formed so as to satisfy the following relationship. 3. A lens, an image receiving surface for receiving an optical image transmitted through the lens, a first reflecting mirror, and a second reflecting mirror for reflecting the light reflected by the first reflecting mirror toward the lens. And the reflecting surfaces of the first reflecting mirror and the second reflecting mirror are formed in a shape such that the optical image magnification at the central portion of the image receiving surface is smaller than that at the peripheral portion of the image receiving surface. Characterized optical device. 4. The camera according to claim 1, wherein the reflecting surfaces of the first reflecting mirror and the second reflecting mirror are formed so as to satisfy the following relationship. 5. The second reflecting surface has an opening centered on the optical axis, and the second lens is arranged in this opening. The optical device according to. 6. The first lens and the second lens are covered by a substantially hemispherical or substantially dome-shaped transparent cover which is symmetrical about the optical axis. The optical device according to any one of claims. 7. An optical system including a lens or a reflecting mirror, and an image receiving surface for receiving the light guided by the optical system, wherein the optical system has a light image magnification ratio in a central portion of the image receiving surface and a peripheral portion of the image receiving surface. The optical device is designed to be larger than the optical image magnification ratio in. 8. An optical system including a lens or a reflecting mirror, and an image receiving surface for receiving the light guided by the optical system, wherein the optical system has a light image enlargement ratio in a central portion of the image receiving surface. An optical device which is designed to be smaller than the optical image magnification ratio in.