JP7244129B1 - night vision camera - Google Patents

Abstract

A night vision camera having a horizontally wide and vertically narrow field of view with a small number of optical components. A night vision camera that converts heat energy emitted from an object into an electrical signal and displays an image, comprising at least one anamorphic lens having negative power in the horizontal direction and at least one surface of the anamorphic lens. It has an off-axis free-form surface mirror, has an imaging area with a horizontal central viewing angle of 120° or more and a vertical central viewing angle of 30° or less, and the entire imaging area is It is characterized by simultaneous imaging all at once. [Selection drawing] Fig. 1

Description

The present invention relates to a night vision camera with a wide horizontal field of view suitable for detecting people at night.

In order to realize a safe car society, advanced driver assistance systems (ADAS) and autonomous driving are being developed. The ADAS system needs to recognize the surrounding environment such as people and objects around the vehicle and the shape of the road. Various types of cameras such as radar, cameras, LIDAR, near-infrared cameras, and night vision cameras are being developed as "external sensors" for recognizing the external environment.

Of these, night vision is a night vision device, and it is a video device that can detect heat and capture objects even in the dark. Night vision can detect people directly from their body temperature without lighting equipment, so it is possible to detect people with high reliability. Night vision has already been put to practical use in automobiles and is installed in several types of vehicles, mainly luxury vehicles (Patent Document 1). The problem with conventional night vision systems is that the horizontal viewing angle is as narrow as 20° to 30°, making it impossible to detect pedestrians in the vicinity of the vehicle.

On the other hand, in the method using a normal camera, an imaging optical system (wide-angle lens) having a wide viewing angle is used so that a wide range of image information can be obtained with a small number of cameras. However, a vehicle-mounted camera is not required to have a wide viewing angle in all directions, but rather a wide viewing angle in the horizontal direction, but it is not necessary to observe a wide range in the vertical direction. When a wide-angle imaging optical system is configured using an ordinary fisheye lens in an in-vehicle camera, the viewing angle in the vertical direction becomes wider than necessary, resulting in a decrease in pixel utilization efficiency, reflection of high-brightness objects, and distortion of the image. Various problems such as increased distortion occur.

Therefore, an ordinary camera adopts an anamorphic optical system that has different viewing angles in the horizontal direction and the vertical direction. Attempts have been made to realize an imaging optical system that provides an image with less distortion. Patent Documents 2 and 3 disclose examples of a camera that uses an anamorphic lens to achieve different viewing angles in the vertical and horizontal directions. Patent Document 2 achieves a viewing angle of 160×96°, and Patent Document 3 achieves a viewing angle of approximately 200×85°.

Here, the anamorphic lens is a lens that has a rotationally asymmetric shape and has different focal lengths in the horizontal and vertical directions. Cylindrical lenses (lenses with a cylindrical shape cut off) are the simplest anamorphic lenses.

An imaging lens configured by a plurality of lenses including an anamorphic lens for capturing images with different horizontal/vertical viewing angle ratios is sometimes called an anamorphic lens. For the sake of clarity herein, such an imaging lens composed of multiple optical components is referred to as an anamorphic optical system to distinguish it from an anamorphic lens, which is a single optical component.

Japanese Patent Laid-Open No. 60-231193 JP 2006-11093 Japanese Patent No. 4790399

Now consider the functions required for the night vision system. Figure 2 shows a panoramic image taken from the driver's seat of the vehicle in front of the intersection. A preceding automobile 21 is photographed in the center of the screen, and bicycles 22-1 to 22-3 and a pedestrian 23 traveling in the vicinity of the own vehicle are photographed. A viewing angle 24 (24×18°) of a conventional night vision camera is indicated by a square frame in the figure. It can be seen that the conventional night vision system has a narrow viewing angle and cannot detect pedestrians and bicycles near the vehicle.

Next, the viewing angle required for the night vision system will be described with reference to FIG. It can be seen that a vertical viewing angle of about 20° is sufficient if limited to the central portion. The viewing angle in the vertical direction at the ends is preferably larger than the vertical viewing angle at the center, and is preferably about 30°. The optimum vertical viewing angle at the edges depends on where the night vision system is installed. When a vision system is installed, it is desirable that the viewing angle is such that the field of view spreads upward at the edge of the screen. Pedestrians on the side of the vehicle are photographed large at the edge of the horizontal field of view, so it is desirable that the angle of view in the vertical direction is widened at the edge of the field of view.

On the other hand, regarding the horizontal viewing angle, it is necessary to detect pedestrians and cyclists crossing the intersection before the intersection in order to prevent accidents involving pedestrians and cyclists when turning left or right. ° (preferred viewing angle 25) is required to be ±75° (particularly desirable viewing angle 26) or more.

FIG. 4 shows a bird's-eye view of the trajectory of a vehicle turning right or left at an intersection. A horizontal viewing angle (25) of at least 120° in order to detect pedestrians crossing an intersection when turning left and to prevent accidents involving pedestrians, particularly preferably 150° or more in order to detect pedestrians in front of the sidewalk. It can be seen that a viewing angle (26) of . It can be seen that it is difficult to detect a pedestrian at an intersection about to turn left or right at a viewing angle (24) of 24° for a conventional night vision camera.

From the above considerations, it can be seen that the desirable viewing angle of the night vision system is about 20° in the vertical center and 120-150° or more in the horizontal direction. It is also desirable that the vertical viewing angle expands from center to edge. A camera with such an extreme horizontal field of view has not been realized so far, not only as an in-vehicle night vision system, but also as a normal in-vehicle camera. The present invention has been made in consideration of the performance truly required for a night vision system and to realize an ideal night vision system.

For the purpose of detecting pedestrians at night with the night vision system, automobiles equipped with a night vision system that displays an image of thermal energy emitted from an object as shown in Patent Document 1 have been put on the market. The problem with conventional night vision systems is that the horizontal viewing angle is as narrow as 20° to 30°, making it impossible to detect pedestrians near automobiles. This is because it is difficult to design and manufacture an optical system with a wide field of view, such as a fish-eye lens used for visible light or near-infrared light, for night vision, and it has been difficult to widen the viewing angle.

On the other hand, night vision systems using visible light and near-infrared light have a high degree of freedom in optical design, and optical systems with various features have been designed. This is because optical materials such as glass and plastic can be used in the visible light and near-infrared regions, and it is easy to manufacture an aspherical lens by molding.

As shown in Patent Documents 2 and 3, in order to achieve a wide field of view in the horizontal direction and a narrow field of view in the vertical direction, an anamorphic optical system with different magnifications in the horizontal and vertical directions, which is necessary for a normal in-vehicle camera, is also used. Adopted. In Patent Document 2, six lenses including an aspherical lens and an anamorphic lens are used to achieve a horizontal viewing angle of 160° and a vertical viewing angle of 96° (horizontal/vertical viewing angle ratio of 1.67). In Patent Document 3, an optical system with a horizontal viewing angle of 200° and a vertical viewing angle of 86° (horizontal/vertical viewing angle ratio of 2.3) is realized using ten lenses including an aspherical lens and an anamorphic lens. ing.

Even in the vehicle-mounted camera having the above-described anamorphic optical system, the ratio of horizontal and vertical viewing angles was about 2.5. As already mentioned, reliable detection of pedestrians on the road requires a horizontal/vertical viewing angle ratio of 4 or more. This is because the difference between the focal lengths in the horizontal direction and the vertical direction becomes too large, making it difficult to correct curvature of field and astigmatism. Until now, no vehicle-mounted camera has been realized that has a large horizontal/vertical viewing angle ratio of 30° or less in the vertical direction and 120° or more in the horizontal direction, which are truly necessary for pedestrian detection.

In practice, when a fish-eye lens or the above-described anamorphic optical system is used, upper and lower imaging regions that are not necessary for the vehicle-mounted camera are cut off and displayed. However, in such a system, only a part of the effective area of the image pickup device is used, resulting in problems such as a decrease in resolution and an increase in cost.

The method of cutting out and using a part of the imaging screen can be used with visible cameras and near-infrared cameras, which are inexpensive and tend to have high resolution, but cannot be used with night vision, which has a high cost per pixel.

A fisheye lens or an anamorphic optical system with different vertical and horizontal magnifications has not been implemented in the night vision system. This is because the glasses and plastics used as lenses in the visible and near-infrared light regions absorb the far-infrared rays used in night vision systems, so special and expensive materials such as germanium, ZnSe, and chalcogenide are used as lens materials. This is because the optical design is restricted because these materials are difficult to process.

For example, as a visible light camera having an anamorphic field of view, Patent Document 2 uses six lenses including an anamorphic lens, and Patent Document 3 uses ten lenses including an anamorphic lens. It is It was not realistic in terms of both accuracy and cost to realize such a large number of lenses using far-infrared lenses, which are difficult to process and expensive.

As described so far, an image device with an anamorphic field of view has not been realized in an in-vehicle night vision camera that images thermal energy radiated from an object. Image devices with an anamorphic field of view have been put into practical use for some ordinary vehicle-mounted cameras, but the horizontal/vertical viewing angle ratio is generally 3 or less, and the horizontal/vertical viewing angle ratio is 4 or more. An in-vehicle camera with value has not been realized.

As a camera capable of increasing the horizontal/vertical viewing angle ratio, conventionally, there are cases where a scanning camera is used. It is called a line scan camera that synthesizes a wide field of view by connecting narrow imaging areas while rotating the camera, and a LIDAR scanner that realizes a wide field of view by scanning a point-like or linear illumination light source and detecting reflected light. A camera of the type has been proposed. With such a system, the field of view in the direction of rotation can be freely expanded, so a camera with an extreme horizontal-to-vertical viewing angle ratio can be realized. However, these methods require moving parts to scan the camera and lighting equipment, making the equipment complex and expensive. In addition, the synchronism of images is lost because the imaging area is sequentially scanned and images are synthesized. There is

SUMMARY OF THE INVENTION It is an object of the present invention to provide an in-vehicle night vision system having a high horizontal/vertical viewing angle ratio.

In order to solve the above-mentioned problems, the present invention uses a night vision camera including an anamorphic lens having negative power in the horizontal direction and at least one aspherical free-form surface mirror arranged off-axis. The viewing angle at the central portion in the direction is 120° or more, the viewing angle at the central portion in the vertical direction is 30° or less, and the entire imaging area is simultaneously imaged.

According to the present invention, by constructing a night vision camera using an anamorphic lens having a negative power in the horizontal direction and at least one aspherical free-form surface mirror arranged off-axis, the central field of view in the horizontal direction is It has become possible to set the viewing angle to 120° or more and the viewing angle to be 30° or less at the center in the vertical direction. Furthermore, by using the optical system of the present invention, it becomes possible to reduce the total number of optical parts, and it becomes possible to reduce the manufacturing cost of the night vision camera.

As already mentioned, it can be seen that a visual field angle of about 20° is sufficient for the vertical direction, as long as it is limited to the center of the field of view. It is desirable that the viewing angle in the vertical direction at the edge is about 30°. On the other hand, the horizontal viewing angle is required to be at least 120°, preferably 150° or more, in order to prevent accidents involving pedestrians and bicycles when turning right or left.

As for the viewing angle in the vertical direction, 20° is sufficient if the viewing angle is stable. Increasing the field of view in the vertical direction lowers the effective utilization rate of the pixels and lowers the resolution. From the results of the inventor's road imaging test, it is found that the central vertical field of view of 15° is acceptable if the night vision system is properly installed in the vehicle.

The present invention has been devised to achieve the viewing angle performance that is truly required for an in-vehicle night vision system as described above.

<Example 1>
In order to achieve the above viewing angles in night vision, we designed an optical system using an anamorphic lens and an off-axis aspherical free-form mirror. FIG. 1 shows the configuration of the optical system of a night vision camera having an anamorphic optical system. The top shows horizontal structures and the bottom shows vertical structures.

In order from the object side, an anamorphic lens 1 having negative power in the horizontal direction, a first free-form surface mirror 2-1 having a convex shape arranged off-axis, and a second concave surface mirror 2-1 arranged off-axis. It consists of a free-form surface mirror 2-2 and an imaging device 3 sensitive to far infrared rays. A dashed line represents a representative ray 10 . By arranging the two mirrors at an angle, the optical path interference is avoided.

A horizontally incident light beam passes through the anamorphic lens 1 having negative power, is refracted, and travels toward the first free-form surface mirror 2-1. The action of this concave lens expands the viewing angle in the horizontal direction. A light ray transmitted through the lens is reflected by the first free-form curved mirror 2-1 having a convex shape, and is turned back toward the second free-form curved mirror 2-2 having a concave shape. The light rays are condensed by the second free-form surface mirror 2 - 2 and form an image on the imaging element 3 .

A light beam incident in the vertical direction passes through the anamorphic lens 1 which has no power in the vertical direction, is reflected by the first free-form surface mirror 2-1 having a convex shape, and is reflected by the second free-form surface mirror 2-1 having a concave shape. Head to Mirror 2-2. The light is condensed by the second free-form surface mirror 2 - 2 having a concave shape and forms an image on the imaging element 3 . The optical system shown in FIG. 1 from which the anamorphic lens 1 is removed constitutes an optical system called an off-axis Schwarzschild optical system. The off-axis Schwarzschild optical system is used in astronomical telescopes and the like as an optical system that is bright because there is no shielding and can obtain a relatively wide angle of view. However, the upper limit of the viewing angle obtained by the off-axis Schwarzschild optical system is about 20 to 30°, which is sufficiently large for a telescope but insufficient for a vehicle-mounted camera.

The optical system shown in FIG. 1 has an anamorphic lens 1 arranged on the incident side of this off-axis Schwarzschild optical system. A horizontally incident light ray is refracted by the anamorphic lens 1 and enters the off-axis Schwarzschild optical system at a small angle of incidence. Since the anamorphic lens 1 has no power in the vertical direction, it has optical characteristics similar to those of a normal off-axis Schwarzschild optical system.

The addition of the anamorphic lens 1 changes the horizontal focal position from the vertical focal position. In order to adjust this focus position, the first free-form curved mirror 2-1 and the second free-form curved mirror 2-2 are designed as free-form curved mirrors having anamorphic shapes.

In night vision optical systems, thermal noise has a large effect on image quality, so an optical system that can capture as much thermal energy as possible is required. Comparing the structure in the horizontal direction and the vertical direction in the optical system shown in FIG. However, in the vertical direction (lower diagram), only the light rays reflected upward by the first free-form curved mirror 2-1 are condensed by the second free-form curved mirror 2-2 and reach the image sensor 3. FIG. For this reason, the light collecting efficiency in the vertical direction is lower than that in the horizontal direction.

A night vision optical system is ideally required to have a numerical aperture of 1.4 or less, and practically it is required to have a numerical aperture of 2 or less. As shown in Fig. 1, θ1 > 20° (horizontal numerical aperture < 1 .4), preferably designed for θ2 >14.4° (vertical numerical aperture <2.0).

Here, the anamorphic lens 1 is a meniscus lens made of germanium having negative power, and an anti-reflection film corresponding to a wavelength of 8 to 14 μm is vapor-deposited on both surfaces. Considering the ease of manufacture, a lens with a simple cylindrical shape with two circular cross sections in the horizontal direction and a rectangular cross section in the vertical direction was adopted. The two free-form surface mirrors 2-1 and 2-2 were formed by evaporating gold onto molded PMMA resin.

As the imaging element 3 sensitive to far-infrared rays, FPA (Focal Plane Arrays) were used in which vanadium oxide elements, which change resistance due to changes in temperature due to radiant energy, were formed in a two-dimensional lattice. A sensor with 640 horizontal pixels and 480 vertical pixels (aspect ratio 4:3) was used.

Actually, in order to avoid the influence of the external environment, the optical system shown in FIG. .

FIG. 5 shows the result of simulating the field of view of the optical system of FIG. A field of view corresponding to each sensor position of 169 points (13×13) obtained by dividing a rectangular effective area of 640×480 pixels of the imaging device into 12 vertically and horizontally is shown. A viewing angle of 18° is obtained at the center of the vertical viewing field, and a viewing angle of 150° at the center of the horizontal viewing field is obtained. The horizontal/vertical viewing angle ratio is 8.3, which is a very large value that cannot be obtained with conventional optical systems.

The distance between dots increases from the center to the periphery in both the horizontal and vertical directions, with high magnification at the center and low magnification at the periphery. The vertical field of view at the horizontal ends is 42°, and the vertical field of view at the horizontal center is 18°.

Also, looking at the horizontal direction, the field of view is 0 to 9 degrees (viewing angle 9 degrees) in the area 1/6 from the center on the sensor, while the field of view per pixel widens toward the outer periphery by 5/5. 6 to the outermost region, the corresponding viewing angle is 60 to 75° (viewing angle 15°). Also in the horizontal direction, the central portion has a higher resolution than the edge portion.

When the resulting field of view is superimposed on the image from the driver's seat shown in FIG. has a wide vertical field of view (42°), and it can be seen that an almost ideal viewing angle is obtained for an in-vehicle night vision system. However, as can be seen from the distribution of points in the screen, the captured image is greatly distorted, and distortion correction of the image is required to make it an image that is easily recognizable by humans. This distortion correction technique will be described later.

An image sensor that has high resolution in the center of the field of view and decreases in resolution toward the edges of the field of view is called a foveal sensor, and it is a sensor that is being researched because it has characteristics similar to human vision. be. Conventional imaging devices are generally designed to provide uniform images with little distortion from the center of the screen to the edge of the screen. In the conventional apparatus, increasing the resolution causes an increase in the amount of image data, and there is a problem that the load of image calculation increases.

The foveal sensor, which can increase the resolution of only the necessary part, can realize not only cost reduction of the imaging device but also cost reduction and speedup of the entire system including the image processing device. This is particularly useful for in-vehicle camera systems (night vision systems) that require high-speed image recognition.

The characteristics of high resolution in the center of the field of view and lower resolution toward the edges of the field of view are, as already mentioned, that in the in-vehicle night vision system, distant pedestrians appear small in the center of the screen, while pedestrians appear small at the edges of the screen. , which corresponds to the fact that nearby pedestrians are magnified, efficiently detects pedestrians farther away, and accurately recognizes nearby pedestrians by capturing the entire body of pedestrians near the vehicle. make it possible to

FIG. 6 shows an overall block diagram of a night vision system including the night vision camera of the present invention. A distorted wide-angle image acquired by the night vision camera of the present invention is sent to an image processing device and subjected to image processing such as brightness adjustment and noise removal. The image after image processing is sent to an image recognition unit that uses machine learning to recognize pedestrians, automobiles, two-wheeled vehicles, etc. around the vehicle. Recognition is performed using distorted image data acquired by night vision. Night vision systems use algorithms and machine learning to recognize pedestrians and vehicles. When a recognition technique based on machine learning is used, since the distortion characteristics of the image are fixed, the distorted image can be directly learned and recognized without performing distortion correction.

With conventional camera technology, distorted images are unnatural and difficult to see, so optical design has been carried out to minimize screen distortion, which has been the reason for hindering the realization of extreme horizontal-to-vertical viewing angle ratios. . In image recognition using machine learning, it is possible to learn including the influence of image distortion, so it has become possible to accurately recognize pedestrians from distorted images.

For this reason, it has become possible to design an optical system that allows image distortion (field distortion), and it has become possible to realize a large horizontal-to-vertical viewing angle ratio of 4 or more.

However, since the display screen viewed by the driver is recognizable by humans, it is necessary to correct the distortion of the image. Distorted image data obtained by night vision is converted into equidistant projection coordinates using the field distortion data shown in FIG. 5 and displayed on the image display device. Night vision images have lower resolution than normal camera images and are grayscale images without color, so even if some image distortion remains, it does not look unnatural, and can be processed at high speed with a light computational load. Distortion correction can be performed.

The position and size of the pedestrian obtained by image recognition are subjected to coordinate transformation, and the presence of the pedestrian is superimposed on the image display device with a square frame. This makes it possible to inform the driver of the existence of the pedestrian in an easy-to-understand manner.

The image recognition device determines the degree of risk of pedestrian contact with a vehicle according to the situation of the pedestrian obtained by image recognition. The danger is notified to the driver by sounds, lights, and images by means of a warning device or an image display device. Furthermore, when it is determined that there is a danger with a high degree of urgency, a signal is sent to the vehicle control device and the vehicle control device operates the emergency automatic brake. The image recognition result and the corrected image are sent to a recording device and the data are saved.

Here, an overall image of the vehicle control system centering on the night vision camera of the present invention is shown, but various sensors are installed in the vehicle having the advanced driving support system. Ordinary cameras, near-infrared cameras, radars, lidars, millimeter-wave radars, etc. may be installed. In such cases, a method called sensor fusion may be used in which multiple sensors are integrated to obtain a more accurate understanding of the vehicle's surroundings.

If the vehicle has such an integrated sensor system, it is also possible to input the image from the night vision system of the present invention into the integrated sensor system, and perform everything from image recognition to vehicle control in the integrated system. is.

Alternatively, it is also possible to recognize a pedestrian by the image processing unit of the night vision system of the present invention and input the recognition result to the integrated sensor system to control the vehicle.

An actual thermal image captured by the night vision of this embodiment is shown in FIG. It can be seen that an automobile 21, a bicycle 22, and a pedestrian 23 are photographed in a wide field of view. FIG. 7 shows an image after the distortion correction, and the viewing angle is obtained almost as designed. It can be seen that the field of view, which is narrow in the vertical direction and wide in the horizontal direction, is obtained, which is desirable for a night vision system.

<Example 3>
FIG. 8 shows the configuration of the optical system of a night vision camera with a different design based on the same concept as that of the first embodiment. As in Example 1, in order from the object side, an anamorphic lens 1 having a negative power in the horizontal direction, a first free-form surface mirror 2-1 having a convex shape arranged off-axis, and an off-axis arranged It is composed of a second free-form surface mirror 2-2 having a concave shape and an imaging element 3 sensitive to far infrared rays. In this design, the anamorphic lens 1 is made smaller and has a higher curvature than the design example of FIG.

By reducing the size of the anamorphic lens 1, the cost of the anamorphic lens 1 can be reduced, and by increasing the curvature, the viewing angle can be expanded. In the optical system shown in FIG. 8, a horizontal/vertical viewing angle ratio of 9 can be realized at a horizontal viewing angle of 180° and a vertical viewing angle of 20°. Furthermore, an effective numerical aperture of 1.5 was realized. As a result of detailed simulations, it was found that it is effective to make the anamorphic lens 1 highly curved in order to achieve such a wide field of view in the horizontal direction and a small numerical aperture. This is because the position of the entrance pupil can be brought closer to the first free-form surface mirror 2-1 by increasing the curvature of the anamorphic lens 1. FIG.

As shown in FIG. 8, when the distance between the anamorphic lens 1 and the first free-form surface mirror 2-1 is d, the focal length f of the anamorphic lens 1 is designed to be f<d/2. This makes it possible to achieve both a wide horizontal viewing angle and a small numerical aperture.

<Example 3>
As a third example, an example of a different optical design is shown in FIG. The top shows horizontal structures and the bottom shows vertical structures. This example also uses one anamorphic lens and two off-axis aspherical free-form mirrors.

In order from the object side, an anamorphic lens 1 having negative power in the horizontal direction, a first free-form surface mirror 2-1 having an off-axis concave surface shape, and a second off-axis concave surface mirror 2-1. It consists of a free-form surface mirror 2-2 and an imaging device 3 sensitive to far infrared rays. A dashed line represents a representative ray 10 . This configuration also avoids the interference of light rays by arranging two mirrors at an angle.

This structure is based on an optical system called the Cross-Dragon optical system, which is designed so that light rays intersect with two anamorphic aspherical mirrors that are compact and can achieve a wide field of view. An anamorphic lens 1 is installed on the incident side of the Cross-Dragon optical system. Both the first free-form curved mirror 2-1 and the second free-form curved mirror 2-2 are anamorphic aspherical mirrors.

The advantage of this optical system is that the light rays are crossed by two off-axis concave mirrors, resulting in a relatively large numerical aperture. An effective numerical aperture of 1.4 is obtained. Noise is an issue for uncooled night vision. By increasing the numerical aperture of the optical system, more light energy can be taken in, making it possible to suppress noise.

Another advantage of this optical design is that the crossing of the light rays allows the night vision camera to be made smaller. For in-vehicle applications, miniaturization of night vision cameras can reduce restrictions on installation positions and avoid adverse effects on design.

As the anamorphic lens 1, a chalcogenide meniscus lens having negative power was used. The anamorphic lens 1 has an antireflection film corresponding to 8-14 μm wavelength on the back surface and a diamond-like carbon (DLC) film designed to have an antireflection function on the front surface. The anamorphic lens 1 is designed to have a circular cross-section on the object side and a non-circular surface on the mirror side. The lens has a cylindrical shape with a square cross section in the vertical direction. The anamorphic lens 1 was formed by molding chalcogenide in order to reduce costs during mass production. The free-form surface mirror was formed by evaporating aluminum onto molded polycarbonate resin.

As the imaging element 3 sensitive to far-infrared rays, FPA (Focal Plane Arrays) were used in which vanadium oxide elements, which change resistance due to changes in temperature due to radiant energy, were formed in a two-dimensional lattice. A microbolometer sensor with 384 horizontal pixels and 288 vertical pixels (aspect ratio 4:3) was used.

FIG. 10 shows simulation results of the field of view of the anamorphic optical system of FIG. The field of view corresponding to 169 sensor positions obtained by dividing the effective area of 384×288 pixels into 12 vertically and horizontally is shown. A viewing angle of 15° is obtained at the center of the vertical viewing field, and a viewing angle of 120° at the center of the horizontal viewing field (horizontal-to-vertical viewing angle ratio of 8) is obtained.

<Example 4>
A fourth optical design for night vision with an anamorphic ultra-wide-angle imaging area is shown in FIG. In this example, one anamorphic lens and three off-axis aspherical free-form mirrors are used. The top shows horizontal structures and the bottom shows vertical structures.

In order from the object side, an anamorphic lens 1 having negative power in the horizontal direction, a first free-form curved mirror 2-1 having an off-axis concave surface shape, and an off-axis convex surface mirror 2-1. It is composed of two free-form surface mirrors 2-2, a third free-form surface mirror 2-3 having a concave surface shape arranged off-axis, and an imaging device 3 sensitive to far infrared rays. A dashed line represents a representative ray 10 .

The anamorphic lens 1 employs a zinc sulfide meniscus lens with negative power. Lens processing was performed by molding, an antireflection film was vapor-deposited on the back surface, and diamond-like carbon was vapor-deposited on the front surface.

By using three mirrors in this configuration, it is possible to reduce aberrations at the edges of the field of view and obtain high resolution from the center of the field of view to the edges of the field of view. However, by using three mirrors, there is a problem that the cost of optical parts increases and the difficulty of optical adjustment increases.

In the case of using a three-surface mirror, it is possible to design a wide variety of optical designs by combining concave and convex surfaces, intersecting or folding light rays, and not limited to this example. In the case of a night vision system, a nearby pedestrian is captured larger at the edge of the screen than at the center of the screen, so high resolution is not necessarily required at the edge of the screen.

However, when considering other uses such as monitoring, there are cases where high resolution is required at the screen edges. For example, it is installed on the wall surface of a corridor, and it is used as a monitoring range of 180 degrees to the left and right. In this case, since a distant person is photographed at the edge of the screen, high resolution is required at the edge of the screen. For such applications, a design using a three-sided mirror is particularly effective.

<Example 5>
FIG. 12 shows a fifth configuration of a night vision optical system with an anamorphic ultra-wide-angle imaging area. In this example, it is composed of one anamorphic lens 1, two rotationally symmetrical lenses, and an aspheric free-form surface mirror 2 having a convex shape in the horizontal direction. The top shows horizontal structures and the bottom shows vertical structures.

In order from the object side, a free-form surface mirror 2 having a horizontally concave shape arranged off-axis, an anamorphic lens 1 having negative power, a rotationally symmetrical first lens 4-1 arranged off-axis, , a second lens 4-2 arranged on the same optical axis as the first lens 4-1, and an imaging device 3 sensitive to far infrared rays. A dashed line represents a representative ray 10 .

In this optical system, the first lens 4-1 and the second lens 4-2 constitute an imaging lens. A free-form surface mirror 2 having a horizontally convex shape is arranged in front of this imaging lens (on the object side). In this optical system, a wide field of view is realized by reflecting horizontal light rays incident at a wide angle toward an imaging device 3 by a free curved surface mirror 2 having a convex shape. On the other hand, the free-form surface mirror 2 has a substantially linear shape in the vertical direction, and incident light is reflected toward the imaging device 3 .

Although the free-form surface mirror 2 provides a wide field of view in the horizontal direction, the effect of the free-form surface mirror 2 greatly deviates the focal position in the horizontal and vertical directions, resulting in a problem of reduced resolution.

An anamorphic lens 1 is arranged between the first lens 4-1 and the free-form surface mirror 2 to correct this horizontal/vertical focus difference.

The anamorphic lens 1 used is a simple cylindrical lens that has a negative power in the vertical direction (concave shape) and a planar shape in the horizontal direction.

The free-form surface mirror 2 is arranged at an angle to the sensor in order to avoid reflection of the imaging device.

Therefore, there arises a problem that the focal position in the vertical direction changes depending on the image height. In order to correct this focal shift, the lens group consisting of the anamorphic lens 1, the first lens 2-1, and the second lens 2-2 is structured to be tilted with respect to the image sensor 3. (tilt lens arrangement).

The tilt angle of the lens group is such that the plane perpendicular to the optical axis of the lens group at the pupil position of the lens group, the tangential plane at the intersection of the free-form surface mirror 2 and the optical axis, and the plane including the imaging surface of the imaging element 3 are straight lines. The tilt of the image plane is corrected by setting the angle so that the two intersect at .

An anamorphic lens 1 is used to correct the horizontal and vertical focus difference. For the focal length f of the anamorphic lens 1 in the vertical direction, d is the distance between the anamorphic lens 1 and the free-form surface mirror 2, and r is the radius of curvature of the free-form surface mirror 2 at the position where the optical axis ray is reflected. when 0.8 x (d + r/2) < f < 1.2 x (d + r/2)
By setting within the range of , it is possible to match the focal positions of the image in the horizontal and vertical directions.

By using the optical system of FIG. 12, a viewing angle exceeding 180° in the horizontal direction can be realized. Also, the viewing angle in the vertical direction can be controlled by changing the shape of the free-form surface mirror in the horizontal direction. In the optical system of this example, a viewing angle of 210° in the horizontal direction and 15° in the vertical direction was obtained by providing a small concave shape in the vertical direction (horizontal/vertical viewing angle ratio of 14).

<Example 6>
A sixth optical design for night vision with an anamorphic ultra-wide-angle imaging area is shown in FIG.

In order from the object side, a free-form surface mirror 2 having a horizontally concave shape placed off-axis, an anamorphic lens 1 having negative power, and a first lens 4 having a rotationally symmetrical shape placed off-axis. -1, a second lens 4-2, and an imaging device 3 sensitive to far infrared rays. A dashed line represents a representative ray 10 .

Also in this optical system, the first lens 4-1 and the second lens 4-2 constitute an imaging lens. By arranging a concave free-form surface aspherical mirror 2 in front of the imaging lens, a wide field of view is realized only in the horizontal direction as shown in the figure. Again, an anamorphic lens 1 is placed between the first lens 4-1 and the mirror to correct for horizontal and vertical focus differences.

The first lens 4-1, the second lens 4-2, and the anamorphic lens 1 share the optical axis, and the lens group consisting of these three lenses is tilted with respect to the free-form surface mirror 2 and the image sensor 3. It is the same as that of the fifth embodiment.

For the vertical focal length f of the anamorphic lens 1, let d be the distance between the anamorphic lens 1 and the free-form surface mirror 2, and r be the distance ratio radius at the position where the optical axis ray of the free-form surface mirror 2 is reflected. When 0.8 x (dr/2) < f < 1.2 x (dr/2)
By setting within the range of , it is possible to match the focal positions of the image in the horizontal and vertical directions. The reason why the reference numerals are reversed from those in the fifth embodiment is that the reflected image is formed inside the concave mirror. Although an anamorphic lens with negative power is used here, it is also possible to use an anamorphic lens with positive power. In that case, the surfaces with positive lens power are placed horizontally instead of vertically.

In this embodiment, a concave aspherical free-form surface mirror is used. Using a concave mirror limits the horizontal viewing angle more than using a convex mirror, but because the reflected horizontal rays intersect near the mirror, an optical window protects the mirror from the environment. (not shown in the drawing) can be miniaturized. In this case, the size of the optical window can be minimized by arranging the optical window near the intersection of the light beams. As the optical window, a germanium flat window with antireflection films on both sides was used.

The optical system of this embodiment realized 150° in the horizontal direction and 20° in the vertical direction (horizontal/vertical viewing angle ratio of 7.5).

All the embodiments up to this point have been described with respect to the in-vehicle night vision system. However, the optical system of the present invention is not limited to night vision, and can also be applied to visible light cameras and near-infrared cameras. The field of view required for a night vision system is the same for a normal visible light camera and a near-infrared camera. A wide field of view can be realized.

Furthermore, although all the embodiments relate to a vehicle-mounted night vision system, the scope of application of the present invention is not limited to this. It can be applied to applications that require a wide field of view in one direction and a narrow field of view in an orthogonal direction. For example, when considering application to traffic monitoring at intersections, it is conceivable that the camera of the present invention is installed at a traffic light to detect pedestrians before and after crossing and to control signals.

Also, by installing it on a train platform and monitoring the flow of passengers on the platform, it is possible to prevent accidents on the platform. It can also be used to monitor pedestrians by installing it in an underpass passage or a pedestrian bridge.

In this specification, the application to night vision for in-vehicle use has been described, so the viewing angle is wide in the horizontal direction and narrow in the vertical direction. It is also possible to provide images with narrow and wide vertical viewing angles.

When mounted on a flying object such as a drone, by mounting the night vision camera downward, it is possible to make the field of view in the front, back, left and right directions anamorphic instead of in the horizontal and vertical directions.

FIG. 2 is a configuration diagram showing the optical system of the night vision camera of Example 1; A panoramic image of the intersection taken from the driver's seat. FIG. 2 illustrates the preferred viewing angles of a night vision system; A comparison diagram of the field of view of the night vision system when turning left or right. 4A and 4B are diagrams showing the viewing range of the ultra-wide-angle optical system of Example 1. FIG. Overall configuration diagram of in-vehicle system 4 is an image captured by the night vision of Example 1 (after distortion correction). FIG. 7 is a configuration diagram showing the optical system of the night vision camera of Example 2; FIG. 11 is a configuration diagram showing the optical system of the night vision camera of Example 3; FIG. 10 is a view showing the visual field range of the super-wide-angle optical system of Example 3; FIG. 11 is a configuration diagram showing an optical system of a night vision camera of Example 4; FIG. 11 is a configuration diagram showing an optical system of a night vision camera of Example 5; FIG. 11 is a diagram showing the configuration of an ultra-wide-angle optical system of Example 6;

1 anamorphic lens 2 free curved surface mirror 2-1 first free curved surface mirror 2-2 second free curved surface mirror 2-3 third free curved surface mirror 3 image sensor 4-1 first lens 4-2 second lens 10 representative Light ray 21 Car 22 Bicycle 23 Pedestrian 24 Viewing angle of conventional night vision 25 Preferred viewing angle (120°)
26 Especially desirable viewing angle (150°)

Claims (2)

A night vision camera that converts thermal energy emitted from an object into an electrical signal and displays an image, comprising an anamorphic lens having negative horizontal power in order from the object side, and at least two off-axis lenses. and an imaging device sensitive to far-infrared rays with pixels arranged in a two-dimensional array. A night vision camera having an imaging area with an angle of 30° or less, and capable of simultaneously capturing an image of the entire imaging area. A night vision camera that converts heat energy emitted from an object into an electrical signal and displays an image, and consists of a free-form surface mirror placed off-axis in order from the object side, and a single off-axis anamol. It is composed of a Fick lens, an imaging lens, and an imaging device having sensitivity to far infrared rays in which pixels are arranged in a two-dimensional array, and has a viewing angle of 120° or more at the central portion in the horizontal direction, and A night vision camera, characterized in that it has an imaging area with a viewing angle of 30° or less in the central portion in the vertical direction, and the entire imaging area is simultaneously imaged.

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