The present invention relates to a wide-angle imaging apparatus that can produce a panoramic image covering an ultra-wide range by using the combination of reflection surfaces and the combination of lenses.
Various research and development have been conducted on a wide-angle imaging apparatus to efficiently produce an image of an object in a large area. One example is the development of a wide-angle camera with a fish-eye lens.
JP 10(1998)-54939 A (REFLECTION TYPE VIEWING ANGLE CONVERTING OPTICAL DEVICE AND OPTICAL SYSTEM USING THE DEVICE) proposes a system that produces an image of a wide visual field by variously changing the shapes of three mirror surfaces arranged opposite to each other. JP 2000-4383 A (MULTIDIRECTIONAL IMAGE TAKING-IN DEVICE) proposes an optical system that produces a counter image inside a normal image by using a shaft of a panoramic image block as a lens.
JP 2001-94839 A (WIDE VISUAL FIELD IMAGE PICKUP DEVICE AND WIDE VISUAL FIELD IMAGE PICKUP DISPLAY DEVICE) proposes a device that includes a convex main mirror having a hole in the center, a convex sub-mirror having a hole in the center, and a lens arranged in the hole of the sub-mirror. Rays of light are reflected by the main mirror, further reflected by the sub-mirror, and then are imaged. This image and an image formed by the lens are displayed on the device. WO00/41024 (PANORAMIC IMAGING APPARATUS) proposes a system that provides a substantially flat and stigmatic image plane by using two reflectors such as a convex hyperboloidal mirror and a concave ellipsoidal or spherical mirror, a relay system, and an image sensor.
In recent years, an electrical light receiving element, e.g., a solid-state imaging device has been used often. In this case, optical members such as an optical low-pass filter and a near-infrared cutoff filter are arranged between an imaging lens and the imaging device, and thus a relatively long back focal length is necessary. The optical low-pass filter removes moiré by attenuating a high frequency component not less than a spacial frequency component required for taking pictures. The near-infrared cutoff filter corrects a spectral response of an electrical photoreceptor.
However, a wide-angle imaging optical system using, e.g., a fish-eye lens generally requires many lenses. Therefore, the weight of the optical system is increased, and the apparatus becomes large and expensive. Moreover, the generation of chromatic aberration or the like is a problem, and actually this wide-angle imaging optical system is only used for taking pictures with special techniques.
JP 10(1998)-54939 A discloses the formation of an image in the vicinity of the axial direction, while a means for correcting various aberrations is limited. For a multidirectional image capture device of JP 2000-4383 A, incident light from the object side passes through a peripheral light-transmitting plane and a rotating body before reaching a peripheral light-proof plane. Therefore, a transparent material used for the rotating body is thick, and when the transparent material is resin, it is susceptible to temperature changes and takes longer to be molded. When the transparent material is glass, particularly aspherical glass, considerable cost is involved in polishing the glass.
An image pickup device of JP 2001-94839 A can produce two images simultaneously: an image formed in such a manner that rays of light are reflected by the main mirror, further reflected by the sub-mirror, and then are imaged; and an image formed by the lens that is arranged in the sub-mirror. The optical system includes the convex main mirror, the convex sub-mirror, and the concave lens. Moreover, a master lens should be placed between an imaging device and the sub-mirror. In this case, the F number of the master lens is high, and rays of light entering the master lens are divergent light due to the configuration of the optical system. Consequently, the master lens becomes large and complicated.
A panoramic imaging apparatus of WO00/41024 requires a relay optical system to form an intermediate image in the optical system, and thus the entire length of the optical system is increased, resulting in a larger apparatus.
As described above, when an electrical light receiving element is used, it is necessary not only to ensure a relatively long back focal length so that optical members such as an optical low-pass filter and a near-infrared cutoff filter are provided, but also to correct aberration sufficiently. To achieve this, however, relatively many lenses are required, and an optical design to reduce the number of lenses should be addressed.
To solve the above conventional problems, it is an object of the present invention to provide a wide-angle imaging optical system that can produce a panoramic image covering a maximum horizontal angle of view of 360 degrees as well as an image in the vicinity of the axial direction with a simple structure and has a relatively long back focal length, improved aberration correction, and brightness.
A wide-angle imaging optical system of the present invention includes a refractive optical system, a reflective optical system, and an image-forming optical system. The reflective optical system and the image-forming optical system are arranged in the indicated order as seen from a longer conjugate distance side and constitute a first optical system. The refractive optical system and the image-forming optical system are arranged in the indicated order as seen from the longer conjugate distance side and constitute a second optical system. The reflective optical system includes a first reflection surface that directly reflects rays of light from an object, and a second reflection surface that reflects rays of light from the first reflection surface. An open portion is provided between the first reflection surface and the second reflection surface, and rays of light from the object enter the open portion. Alight-transmitting portion is provided in the second reflection surface and transmits rays of light that have entered the refractive optical system. An aperture is provided in the first reflection surface and allows rays of light from the second reflection surface and the refractive optical system to enter the image-forming optical system.
A wide-angle imaging apparatus of the present invention includes the wide-angle imaging optical system of the present invention and an imaging device for picking up an image formed by the image-forming optical system.
A surveillance imaging apparatus of the present invention includes the wide-angle imaging optical system of the present invention.
A vehicle-mounted imaging apparatus of the present invention includes the wide-angle imaging optical system of the present invention.
A projection apparatus of the present invention includes the wide-angle imaging optical system of the present invention.
The present invention includes the reflective optical system with the first reflection surface and the second reflection surface, the open portion provided between the first reflection surface and the second reflection surface, the light-transmitting portion provided in the second reflection surface, and the aperture provided in the first reflection surface, thereby producing a panoramic image that covers a wide range, i.e., a maximum horizontal angle of view of 360 degrees and a vertical angle of view of about 180 degrees. Moreover, the main optical system can be composed of reflection surfaces that cause no chromatic aberration. This reduces not only man-hours for design but also constraints on fabrication, so that a small, lightweight, low-cost, and bright wide-angle imaging optical system can be achieved.
In the present invention, it is preferable that the first optical system and the second optical system share the image-forming optical system. This configuration can reduce the size of the apparatus.
It is preferable that no intermediate image is formed inside the wide-angle imaging optical system. With this configuration, the wide-angle imaging optical system is not a relay optical system, and the entire length of the optical system is reduced, so that a smaller apparatus can be achieved.
The wide-angle imaging optical system preferably satisfies the relationship expressed by
fa>0
fb>0
where fa is a combined focal length of the first optical system, and fb is a combined focal length of the second optical system. With this configuration, the wide-angle imaging optical system is not a relay optical system, and the entire length of the optical system is reduced, so that a smaller apparatus can be achieved. When fa is not more than the lower limit, an intermediate image is formed inside the first optical system, and thus the image of an object formed by the first optical system is an erect image. Moreover, the first optical system becomes a relay optical system, which increases the entire length of the optical system.
When fb is not more than the lower limit, an intermediate image is formed inside the second optical system, and thus the image of an object formed by the second optical system is an erect image. Moreover, the second optical system becomes a relay optical system, which increases the entire length of the optical system. In this case, when the image formed by the first optical system is inverted, the resultant image is not continuous.
The wide-angle imaging optical system preferably satisfies the relationship expressed by
f2≧d
where f2 is a focal length of the second reflection surface, and d is a distance on the axis between the first reflection surface and the second reflection surface. This configuration easily can correct aberration in the image-forming optical system. When f2≧d is not satisfied, an intermediate image is formed inside the reflective optical system, and the angle of deviation of rays of light passing through the image-forming optical system becomes larger, thus making it difficult to correct aberration in the image-forming optical system. Moreover, the image formed by the first optical system is an erect image. Therefore, when the image formed by the second optical system is inverted, the resultant image is not continuous.
The wide-angle imaging optical system preferably satisfies the relationship expressed by
|f12/fa|>5
where fa is a combined focal length of the first optical system, and f12 is a combined focal length of the first reflection surface and the second reflection surface. This configuration can reduce the entire length of the optical system. |f12/fa| represents the degree of a focal system of the reflection surfaces. When the value is not more than the lower limit, the combined focal length of the first and second reflection surfaces is reduced. Therefore, a relay optical system rather than an a focal system is provided while an intermediate image is formed inside the wide-angle imaging optical system, so that the entire length of the optical system becomes longer.
The wide-angle imaging optical system preferably satisfies the relationship expressed by
r2>0
0.3<r1/r2<0.7
where r1 is a radius of curvature of the first reflection surface, and r2 is a radius of curvature of the second reflection surface. This configuration can achieve a small bright optical system. When r2 is not more than the lower limit, the second reflection surface has a convex surface as seen from incident light from an object, and rays of light entering the image-forming optical system are divergent light. Therefore, the image-forming optical system itself becomes larger, which in turn increases the size of the apparatus.
When the value is not less than the upper limit of 0.3<r1/r2<0.7, rays of light from the second reflection surface enter the aperture at a larger angle, thus making it difficult to correct aberration in the image-forming optical system. Moreover, the aperture efficiency also is reduced, so that brightness cannot be ensured at the periphery. When the value is not more than the lower limit, the area used by the first optical system on the second reflection surface extends to near the central axis, and thus the area of the light-transmitting portion becomes narrower. Consequently, rays of light from the second image-forming optical system do not pass through the light-transmitting portion, and an image cannot be formed.
The wide-angle imaging optical system preferably satisfies the relationship expressed by
|fb−fa|/|fa|<0.5
where fa is a combined focal length of the first optical system, and fb is a combined focal length of the second optical system. This configuration can prevent missing or overlapping of images. When the value is not less than the upper limit of |fb−fa|/|fa|<0.5, a difference in back focal length between the first optical system and the second optical system is increased. Moreover, since the magnification for image formation of the first optical system differs from that of the second optical system, an annular image formed by the first optical system and a circular image formed by the second optical system are not continuous, resulting in missing or overlapping of images.
The wide-angle imaging optical system preferably satisfies the relationship expressed by
1.2<bf/fi<1.8
where bf is a back focal length of the image-forming optical system measured in terms of air when rays of light from an object at infinity enter the image-forming optical system in parallel, and fi is a combined focal length of the image-forming optical system. This configuration can reduce the entire length of the optical system. When the value is not less than the upper limit of 1.2<bf/fi<1.8, the back focal length is increased to make the entire length of the optical system longer, which in turn increases the size of the apparatus. When the value is not more than the lower limit, the back focal length is reduced, and the optical system cannot be provided.
It is preferable that the refractive optical system includes a first lens group with negative power and a second lens group with positive power that are arranged in the indicated order as seen from the object side. With this configuration, the wide-angle imaging optical system does not form any intermediate image at a halfway point, and a bright optical system can be achieved.
It is preferable that at least one of the first reflection surface and the second reflection surface is a rotationally symmetrical aspheric surface in shape. This configuration optimally can correct curvature of field or astigmatism generated in the reflective optical system itself by using an aspherical coefficient.
It is preferable that a magnification for image formation of the first optical system and a magnification for image formation of the second optical system have the same sign. With this configuration, when the image formed by the first optical system is an erect image, the image formed by the second optical system also is an erect image. Moreover, when the image formed by the first optical system is an inverted image, the image formed by the second optical system also is an inverted image. Therefore, a continuous image can be obtained.
It is preferable that a magnification for image formation of the first optical system and a magnification for image formation of the second optical system are both negative. With this configuration, the wide-angle imaging optical system is not a relay optical system, and the entire length of the optical system is reduced, so that a smaller apparatus can be achieved.
It is preferable that at least one focal point of the first reflection surface coincides with at least one focal point of the second reflection surface. A rotationally symmetrical aspheric surface has one or two focal points. This configuration allows a chief ray to converge on the position of the focal point by combining the first reflection surface with the second reflection surface.
It is preferable that a lens stop is located inside the image-forming optical system or between the image-forming optical system and the second reflection surface. With this configuration, one of the focal points of the second reflection surface coincides with the center of the lens stop. Therefore, rays of light can be imaged by the image-forming optical system while a chief ray converges on the position of the lens stop.
It is preferable that a focal point of the second reflection surface coincides with the center of the lens stop.
It is preferable that a shielding member is formed near the periphery of the aperture. This configuration can eliminate ghost light that is reflected four or more times by the reflection surfaces, enters the aperture, and is picked up after passing through the image-forming optical system.
It is preferable that the shielding member supports the image-forming optical system. This configuration can use the shielding member efficiently without relying on a special member for supporting the image-forming optical system.
It is preferable that the image-forming optical system includes a hood that limits rays of light entering the image-forming optical system. This configuration can prevent a circular image of a second imaging area (where rays of light enter the refractive optical system) from overlapping with an annular image of a first imaging area (where rays of light enter the reflective optical system) that is formed outside the circular image when they are picked up by the imaging device.
It is preferable that the lenses of the image-forming optical system are arranged in the following order as seen from the object side: a negative lens, a positive lens, and a positive lens. This configuration allows the image-forming optical system to have a relatively long back focal length, improved aberration performance, and brightness even with a small number of lenses.
It is preferable that the lenses of the image-forming optical system are arranged in the following order as seen from the object side: a negative lens, a positive lens, a positive lens, and a positive lens. This configuration allows the image-forming optical system to have a relatively long back focal length, improved aberration performance, and brightness even with a small number of lenses.
It is preferable that the refractive optical system includes a hood that limits rays of light entering the refractive optical system. This configuration can prevent a circular image of a second imaging area (where rays of light enter the refractive optical system) from overlapping with an annular image of a first imaging area (where rays of light enter the reflective optical system) that is formed outside the circular image when they are picked up by the imaging device.
It is preferable that the first reflection surface is formed integrally with a lens of the image-forming optical system. This configuration can improve the manufacturing cost and efficiency and reduce the number of optical components required for the wide-angle imaging optical system. Moreover, the deviation between the optical axes of optical elements in the reflective optical system and the image-forming optical system is reduced, thereby making the optical system resistant to vibration. Thus, the optical system can maintain high performance, particularly when used as a vehicle-mounted optical system.
It is preferable that the shape of the first reflection surface is substantially the same as the shape of a portion of the lens of the image-forming optical system that corresponds to the aperture.
It is preferable that the shape of the first reflection surface differs from the shape of a portion of the lens of the image-forming optical system that corresponds to the aperture. With this configuration, the lens at the aperture can have the same effect as a convex or concave lens, so that various aberrations generated in the wide-angle imaging optical system can be corrected optimally, thus producing a high-quality image that covers a wide range.
It is preferable that the second reflection surface is formed integrally with a lens of the refractive optical system. This configuration can improve the manufacturing cost and efficiency and reduce the number of optical components required for the wide-angle imaging optical system. Moreover, the deviation between the optical axes of optical elements in the reflective optical system and the refractive optical system is reduced, thereby making the optical system resistant to vibration. Thus, the optical system can maintain high performance, particularly when used as a vehicle-mounted optical system. Further, this configuration combined with the integrally formed first reflection surface and lens of the image-forming optical system enables accurate image display and image processing conversion, since an annular image formed by the first optical system and an annular image formed by the second optical system can have the same central point more precisely.
It is preferable that the shape of the second reflection surface is substantially the same as the shape of a portion of the lens of the refractive optical system that corresponds to the light-transmitting portion. This configuration facilitates processing.
It is preferable that the shape of the second reflection surface differs from the shape of a portion of the lens of the refractive optical system that corresponds to the light-transmitting portion. With this configuration, the lens at the light-transmitting portion can have the same effect as a convex or concave lens, so that various aberrations generated in the wide-angle imaging optical system can be corrected optimally, thus producing a high-quality image that covers a wide range.
It is preferable that the image-forming optical system includes a third reflection surface that reflects rays of light imaged by the image-forming optical system. The third reflection surface can reflect rays of light in the direction substantially perpendicular to the central axis. Therefore, it is possible to increase the optical path length of the wide-angle imaging optical system even in a limited space.
It is preferable that the refractive optical system and the image-forming optical system are transparent to an infrared wavelength region including 1 to 10 μm. With this configuration, the refractive optical system and the image-forming optical system transmit light in a wide range of wavelength regions from visible to infrared. Thus, the apparatus can be used in a wide range of wavelength regions from visible to infrared.
A wide-angle imaging apparatus of the present invention includes the wide-angle imaging optical system of the present invention and an imaging device for picking up an image formed by the image-forming optical system. The wide-angle imaging apparatus can produce a panoramic image that covers a wide range, i.e., a maximum horizontal angle of view of 360 degrees and a vertical angle of view of about 180 degrees. Moreover, the main optical system can be composed of reflection surfaces that cause no chromatic aberration. This reduces not only man-hours for design but also constraints on fabrication, so that a small, lightweight, low-cost, and bright wide-angle imaging apparatus can be achieved.
In the wide-angle imaging apparatus, it is preferable that a plurality of wide-angle imaging optical systems and the imaging devices that correspond to each of the plurality of wide-angle imaging optical systems are arranged so as to produce separate images of an object. This configuration not only can produce a panoramic image that covers a maximum horizontal angle of view of 360 degrees, but also can increase the vertical angle of view compared with the configuration including a single wide-angle imaging optical system.
It is preferable that two wide-angle imaging optical systems and the imaging devices that correspond to each of the two wide-angle imaging optical systems are arranged so as to produce separate images of an object, and when an axis that joins centers of curvature of the first reflection surface and the second reflection surface is identified as a central axis, the two wide-angle imaging optical systems are arranged symmetrically with respect to an axis perpendicular to the central axis.
It is preferable that the plurality of wide-angle imaging optical systems share a single imaging device. This configuration is advantageous for small size and lightweight.
It is preferable that when an area in which rays of light enter the reflective optical system is identified as a first imaging area, and an area in which rays of light enter the refractive optical system is identified as a second imaging area, an image picked up by the imaging device includes a circular image that is obtained by taking the second imaging area and an annular image that is obtained by taking the first imaging area and formed outside the circular image, and that the first imaging area and the second imaging area do not overlap with each other, and further that the circular image and the annular image are arranged continuously. This configuration can use the effective area of the imaging device efficiently, eliminate missing or overlapping of images, and ensure accurate imaging.
It is preferable that a protective member is arranged so as to surround the open portion. This configuration can protect the reflective optical system easily and effectively.
It is preferable that the protective member is provided with a film for preventing internal reflection. This configuration effectively can eliminate ghost light that is reflected internally by the protective member and travels through the same optical path as normal light while protecting the reflection optical system easily and effectively.
It is preferable that the protective member is in the form of a substantially frustoconical, and the inner diameter of the protective member at the first reflection surface differs from the inner diameter of the protective member at the second reflection surface. This configuration can control the reflection angle of ghost light and prevent the ghost light from traveling through the same optical path as normal light.
It is preferable that at least one of the refractive optical system and the image-forming optical system has a zoom function. This configuration can produce an enlarged image of an object in the vicinity of the axial direction.
It is preferable that the wide-angle imaging apparatus can be mounted on an object, and a mounting angle can be adjusted. This configuration easily can change the imaging range.
The wide-angle imaging apparatus preferably includes a moving object sensing function. With this configuration, a moving object can be extracted, and therefore any motion in the surroundings can be detected and recognized precisely.
A surveillance imaging apparatus of the present invention includes the wide-angle imaging optical system of the present invention and thus can produce a panoramic image that covers a wide range of horizontal angle of view as well as vertical angle of view. Moreover, reflection surfaces made of a material that reflects light in a wide range of wavelength regions from visible to infrared are combined with lenses made of a material that transmits light in the visible to infrared wavelength regions. Thus, surveillance covering an ultra-wide range can be performed at any time of day or night.
A vehicle-mounted imaging apparatus of the present invention includes the wide-angle imaging optical system of the present invention and thus can produce a panoramic image that covers a wide range of horizontal angle of view as well as vertical angle of view. The image produced is displayed on a vehicle-installed monitor, which is installed in the vehicle, so that the vehicle-mounted imaging apparatus can be used, e.g., as a rear view monitor, a front view monitor, or a side view monitor.
A projection apparatus of the present invention includes the wide-angle imaging optical system of the present invention and thus can project an image of an object that covers an ultra-wide range by using a projector such as a video projector.
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
The optical system of the wide-angle imaging apparatus in
The first reflection surface 1 has a convex surface as seen from incident light 8b (rays of light from a first imaging area) from the outside (an object). The second reflection surface 2 has a concave surface as seen from the incident light 8b. A lens 6 of the image-forming optical system 5 is formed integrally with the first reflection surface 1, while a lens 4 of the refractive optical system 3 is formed integrally with the second reflection surface 2.
Incident light 8a (rays of light from a second imaging area) from the outside (an object) is refracted by the refractive optical system 3, passes through a light-transmitting portion 2a, i.e., a circular opening provided in the second reflection surface 2 and a circular aperture 1a provided in the first reflection surface 1, then is imaged by the image-forming optical system 5, and picked up by the imaging device 7.
The incident light 8b is reflected successively by the convex surface of the first reflection surface 1 and the concave surface of the second reflection surface 2, passes through the aperture 1a provided in the first reflection surface 1, then is imaged by the image-forming optical system 5, and picked up by the imaging device 7.
The first reflection surface 1 and the second reflection surface 2 are rotationally aspheric surfaces that are symmetrical with respect to the central axis 9. In this embodiment, the first reflection surface 1 and the second reflection surface 2 are obtained by rotating a parabola.
In
Therefore, the incident light 8a, 8b from the outside can enter any position of an angle θ ranging from 0 to 360 degrees, as shown in
It is preferable that a magnification for image formation of the first optical system and a magnification for image formation of the second optical system have the same sign. Thus, when the image formed by the first optical system is an erect image, the image formed by the second optical system also is an erect image. Moreover, when the image formed by the first optical system is an inverted image, the image formed by the second optical system also is an inverted image. Therefore, a continuous image can be obtained. In this case, it is more preferable that the magnification for image formation of the first optical system and the magnification for image formation of the second optical system are both negative. With the negative sign, the wide-angle imaging optical system is not a relay optical system, and the entire length of the optical system is reduced, so that a smaller apparatus can be achieved. The same is true in the following embodiments.
As described above, this embodiment allows the main optical system to be composed of reflection surfaces that cause no chromatic aberration. Therefore, not only man-hours for design but also constraints on fabrication can be reduced, providing a small, lightweight, low-cost, and bright wide-angle imaging apparatus. Moreover, the lenses of the refractive optical system and the reflective optical system and the reflection surfaces that are formed integrally with these lenses have an aspheric surface, so that various aberrations generated in the optical system can be corrected. Further, as shown in
In this embodiment, the first reflection surface 1 and the second reflection surface 2 are rotationally aspheric surfaces obtained by rotating a parabola. However, the reflection surfaces may be obtained by rotating an ellipse including a circle or a hyperbola. The same is true in the following embodiments.
For each of the lenses 4, 6, the portion provided with the reflection surface and the portion corresponding to the light-transmitting portion 2a or the aperture 1a are formed in a continuous uniform shape. However, the lens shape may be changed, e.g., by reversing the convexity and concavity of the lens at the light-transmitting portion 2a or the aperture 1a, which will be described in detail in the following embodiments.
In
For an embodiment as shown in
In
For an embodiment as shown in
Like Embodiment 2, this embodiment can reduce the size of the apparatus by using the third reflection surface. Moreover, the third reflection surface is arranged so as to reflect rays of light in the direction substantially perpendicular to the central axis 9. Therefore, it is possible to increase the optical path length of the wide-angle imaging optical system even in a limited space.
In the configuration in
In the embodiment in
Consequently, in the configuration in
In this configuration, incident light 8a from the outside is refracted by the refractive optical system 3, passes through the light-transmitting portion 2a and the aperture 1a provided in the first reflection surface 1, then is imaged by the image-forming optical system 5, and picked up by the imaging device 7.
Incident light 8b from the outside is reflected successively by the convex surface of the first reflection surface 1 and the concave surface of the second reflection surface 2, passes through the aperture 1a provided in the first reflection surface 1, then is imaged by the image-forming optical system 5, and picked up by the imaging device 7. As described above, when the basic cross section of the lens in the light-transmitting portion or aperture is different from the basic cross section of the lens in a portion provided with the reflection surface, the effect can be comparable to that obtained by arranging a special convex or concave lens separately at the light-transmitting portion or aperture. Moreover, various aberrations generated in the wide-angle imaging optical system can be corrected optimally, thus producing a high-quality image that covers a wide range.
In
Incident light 8b from the outside is reflected successively by the convex surface of the first reflection surface 1 and the concave surface of the second reflection surface 2, passes through the aperture 1a provided in the first reflection surface 1 and the first resin substrate 113, then is imaged by the image-forming optical system 5, and picked up by the imaging device 7.
As described above, the configuration in
The image-forming optical system 5 can be held in contact with the aperture 1a provided in the first reflection surface 1 and the first resin substrate 113. Alternatively, the image-forming optical system 5 also can be held by being inserted into the aperture 1a. Similarly, the refractive optical system 3 can be held in contact with the light-transmitting portion 2a provided in the second reflection surface 2 and the second resin substrate 114. Alternatively, the refractive optical system 3 also can be held by being inserted into the light-transmitting portion 2a. An adhesive or the like may be used to hold the optical systems.
In
In the examples of
The basic configuration and operation of half of the wide-angle imaging optical systems are the same as those in Embodiment 1. Incident light 8a from the outside is refracted by the refractive optical system 3, passes through the light-transmitting portion 2a provided in the second reflection surface 2 and the aperture 1a provided in the first reflection surface 1, then is imaged by the image-forming optical system 5, and picked up by the imaging device 7.
Incident light 8b from the outside is reflected successively by the convex surface of the first reflection surface 1 and the concave surface of the second reflection surface 2, passes through the aperture 1a provided in the first reflection surface 1, then is imaged by the image-forming optical system 5, and picked up by the imaging device 7.
Like Embodiment 1, half of the wide-angle imaging optical systems has a maximum horizontal angle of view of 360 degrees and a maximum vertical angle of view of 180 degrees. In
Similarly, a circular image 135 of the second imaging area and an annular image 136 of the first imaging area appear on a second imaging device 134. Since the imaging range of the first imaging area continues to that of the second imaging area, the circular image 135 and the annular image 136 are formed into a single continuous circular image. Therefore, the effective area of the second imaging device 134 can be used efficiently.
As described above, this embodiment can produce a panoramic image that covers a maximum horizontal angle of view of 360 degrees. Moreover, this embodiment can produce an image at a maximum vertical angle of view of 360 degrees, compared with about 180 degrees in Embodiment 1.
The configuration in
Incident light 8b from the outside is reflected successively by the convex surface of the first reflection surface 1 and the concave surface of the second reflection surface 2, passes thought the aperture 1a provided in the first reflection surface 1, then is imaged by the image-forming optical system 5, reflected by the third reflection surface 61 in one direction, and picked up by the imaging device 7.
The configuration in
Incident light 8b from the outside is reflected successively by the convex surface of the first reflection surface 1 and the concave surface of the second reflection surface 2, passes through the aperture 1a provided in the first reflection surface 1, then is imaged by the image-forming optical system 5, reflected by the third reflection surface 71 in one direction, further imaged by the image-forming optical system 5, and picked up by the imaging device 7.
Like Embodiment 2, half of the wide-angle imaging optical systems has a maximum horizontal angle of view of 360 degrees and a maximum vertical angle of view of about 180 degrees. Therefore, this embodiment also can produce an image at a maximum vertical angle of view of 360 degrees using two wide-angle imaging optical systems.
As in the case of the third reflection surface with a flat surface, this embodiment can make the optical system shorter in the direction of the central axis 9, thus reducing the size of the apparatus. Moreover, the third reflection surface is arranged so as to reflect rays of light that have passed through the aperture 1a in the direction substantially perpendicular to the central axis 9. Therefore, it is possible to increase the optical path length of the wide-angle imaging optical system even in a limited space.
Embodiments 5 to 8 use two wide-angel imaging optical systems of the embodiments as shown in
A third reflection surface 181 with a flat surface corresponding to the left optical system and a third reflection surface 182 with a flat surface corresponding to the right optical system are arranged symmetrically with respect to a centerline 9d. In each of the right and left wide-angle imaging optical systems, incident light 8a from the outside is refracted by the refractive optical system 3, passes through the light-transmitting portion 2a provided in the second reflection surface 2, and enters the aperture 1a provided in the first reflection surface 1. Incident light 8b from the outside is reflected successively by the convex surface the first reflection surface 1 and the concave surface of the second reflection surface 2, and enters the aperture 1a provided in the first reflection surface 1.
The incident light from the left is reflected by the third reflection surface 181 in one direction, the incident light from the right is reflected by the third reflection surface 182 in one direction, and the reflected light is imaged by the lens 183 and picked up by the imaging device 184.
Since the imaging range of the first imaging area continues to that of the second imaging area, the circular image 202 and the annular image 203 are formed into a single continuous circular image, and similarly the circular image 204 and the annular image 205 are formed into a single continuous circular image. Therefore, the effective area of the imaging device 201 can be used efficiently.
In this embodiment, the right and left optical systems share the lens 183 and the imaging device 184, so that the wide-angle imaging apparatus can be reduced in size, weight and cost.
In this embodiment, the right and left optical systems share the prism 191, the lens 183, and the imaging device 184, so that the wide-angle imaging apparatus can be reduced in size, weight and cost further.
The explanation of an image produced by the wide-angle imaging apparatus in this embodiment is the same as that in Embodiment 9 (
The cover 321 is arranged so as to surround the open portion between the first reflection surface 1 and the second reflection surface 2. Therefore, incident light 8b from the outside reaches the first reflection surface 1 through the cover 321. The cover 321 may be used not only in the wide-angle imaging optical system in
In
In the configuration in
The embodiment in
Ghost light 8e entering a space in the cover 321 is cut off at the end of the inner surface of the cover 321. If the ghost light 8e is not cut off, it is reflected by this end, further reflected by the first reflection surface 1, and then reaches the imaging device 7 through the same path as normal light. Thus, this configuration can prevent both of the ghost light 8d and 8e from joining halfway through the optical path of normal light and reaching the imaging device 7.
In this embodiment, the end of the cover 321 is painted black. However, any shielding member can be provided at the end of the cover 321, e.g., the end of the cover 321 may be formed of a shielding material.
The basic configuration of the wide-angle imaging optical system is not limited to the example as shown in
While Embodiment 12 uses the coating 421 to prevent internal reflection so that ghost light does not travel through the same optical path as normal light, this embodiment achieves the same effect with the shape of the cover 441. Specifically, as shown in
Not only the example as shown in
Ghost light 8c is reflected by the reflection surfaces 1 and 2, directed to the reflection surface 1 again, and cut off by the shielding member 1b. When the shielding member 1b is not used, the ghost light 8c is again reflected by the reflection surfaces 1 and 2 (i.e., the ghost light 8c is reflected four times between the reflection surfaces), enters the aperture 1a, then is imaged by the image-forming optical system 5, and picked up by the imaging device 7, as indicated by a broken line.
In the example as shown in
The basic configuration of the wide-angle imaging optical system is not limited to the example as shown in
A hood 462 that is formed, e.g., of a black-painted shielding member, may be provided at the tip of the lens barrel 461. The hood 462 can limit rays of light entering the image-forming optical system 5 and eliminate unwanted light outside the angle of view that causes stray light or flare.
Reflected light may be generated due to rays of light that enter at an angle approximately equal to the inclination angle of the hood. In such a case, the hood surface can be made uneven by forming fine steps like stairs, thus allowing the reflected light to diverge.
In this embodiment, the hood is provided in the image-forming optical system 5. However, the refractive optical system including the lens 3a also may use a hood to limit rays of light entering the refractive optical system.
The basic configuration of the wide-angle imaging optical system is not limited to the example as shown in
In
The shape of the reflection surfaces in this embodiment is a rotationally symmetrical aspheric surface including an aspherical coefficient, and the amount of sag Z is expressed by
where h is a height from the optical axis, R is a radius of curvature of the surface, A2 to A10 are aspherical coefficients, and K is a conical coefficient.
In this embodiment, the first reflection surface of the reflective optical system has a convex surface, and the second reflection surface has a concave surface as seen from incident light from an object. Moreover, the refractive optical system includes a first lens group with negative power and a second lens group with positive power that are arranged in the indicated order from the object side. Thus, the wide-angle imaging optical system does not form any intermediate image at a halfway point, and a bright optical system can be achieved.
The position of a lens stop preferably is located inside the image-forming optical system or between the image-forming optical system and the second reflection surface. With this configuration, one of the focal points of the second reflection surface coincides with the center of the lens stop. Therefore, rays of light can be imaged by the image-forming optical system while a chief ray converges on the position of the lens stop. In this embodiment, the position of the lens stop is set to the vertex of the first reflection surface.
The lenses of the image-forming optical system are arranged in the following order as seen from the object side: a negative lens, a positive lens, a positive lens, and a positive lens. Thus, the image-forming optical system can have a relatively long back focal length, improved aberration correction, and brightness even with a small number of lenses. The lens configuration of the image-forming optical system may be such that a negative lens, a positive lens, and a positive lens are arranged in the indicated order as seen from the object side.
A plate that is inserted between the lens closest to the image side and the imaging device 7 serves as an optical low-pass filter and a near-infrared cutoff filter. In this embodiment, the shape of the first reflection surface differs from the shape of a portion of the lens that corresponds to the aperture 1a. Similarly, the shape of the second reflection surface differs from the shape of a portion of the lens that corresponds to the light-transmitting portion 2a.
In the configurations in
This embodiment preferably satisfies at least one of the following formulas (2) to (9):
fa>0 Formula (2)
fb>0 Formula (3)
f2≧d Formula (4)
|f12/fa|>5 Formula (5)
r2>0 Formula (6)
0.3<r1/r2<0.7 Formula (7)
|fb−fa|/|fa|<0.5 Formula (8)
1.2<bf/fi<1.8 Formula (9)
In the formula (2), fa is a combined focal length of the first optical system. When fa is not more than the lower limit, an intermediate image is formed inside the first optical system, and thus the image of an object formed by the first optical system is an erect image. Moreover, the first optical system becomes a relay optical system, which increases the entire length of the optical system.
In the formula (3), fb is a combined focal length of the second optical system. When fb is not more than the lower limit, an intermediate image is formed inside the second optical system, and thus the image of an object formed by the second optical system is an erect image. Moreover, the second optical system becomes a relay optical system, which increases the entire length of the optical system. In this case, when the image formed by the first optical system is inverted, the resultant image is not continuous.
In the formula (4), f2 is a focal length of the second reflection surface, and d is a distance on the axis between the first reflection surface and the second reflection surface. When the formula (4) is not satisfied, an intermediate image is formed inside the reflective optical system, and the angle of deviation of rays of light passing through the image-forming optical system becomes larger, thus making it difficult to correct aberration in the image-forming optical system. Moreover, the image formed by the first optical system is an erect image. Therefore, when the image formed by the second optical system is inverted, the resultant image is not continuous.
In the formula (5), fa is a combined focal length of the first optical system, and f12 is a combined focal length of the first reflection surface and the second reflection surface. The formula (5) represents the degree of a focal system of the reflection surfaces. When the value is not more than the lower limit, the combined focal length of the first and second reflection surfaces is reduced. Therefore, a relay optical system rather than an a focal system is provided while an intermediate image is formed inside the wide-angle imaging optical system, so that the entire length of the optical system becomes longer.
In the formulas (6) and (7), r1 is a radius of curvature of the first reflection surface, and r2 is a radius of curvature of the second reflection surface. When r2 is not more than the lower limit in the formula (6), the second reflection surface has a convex surface as seen from incident light from an object, and rays of light entering the image-forming optical system are divergent. Therefore, the image-forming optical system itself becomes larger, which in turn increases the size of the apparatus.
The formula (7) represents a ratio of the radius of curvature of the first reflection surface to that of the second reflection surface. When the value is not less than the upper limit in the formula (7), rays of light from the second reflection surface enter the aperture at a larger angle, thus making it difficult to correct aberration in the image-forming optical system. Moreover, the aperture efficiency also is reduced, so that brightness cannot be ensured at the periphery. When the value is not more than the lower limit in the formula (7), the area used by the first optical system on the second reflection surface extends to near the central axis, and thus the area of the light-transmitting portion becomes narrower. Consequently, rays of light from the second image-forming optical system do not pass through the light-transmitting portion, and an image cannot be formed.
The formula (8) represents the relationship in combined focal length between the first optical system and the second optical system and defines a difference between them. When the value is not less than the upper limit in the formula (8), a difference in back focal length between the first optical system and the second optical system is increased. Moreover, since the magnification for image formation of the first optical system differs from that of the second optical system, an annular image formed by the first optical system and a circular image formed by the second optical system are not continuous, resulting in missing or overlapping of images.
In the formula (9), bf is a back focal length of the image-forming optical system measured in terms of air when rays of light from an object at infinity enter the image-forming optical system in parallel, and fi is a combined focal length of the image-forming optical system. When the value is not less than the upper limit in the formula (9), the back focal length is increased to make the entire length of the optical system longer, which in turn increases the size of the apparatus. When the value is not more than the lower limit in the formula (9), the back focal length is reduced, and the optical system cannot be provided.
The formulas (1) to (9) may be applied not only to the configurations in
Example 1 is directed to the wide-angle imaging apparatus in
fa=1.00, Fno=1.94, and ω=30 to 90°.
Table 1 shows numerical values of the first optical system in Example 1, where nd and νd indicate a refractive index and an Abbe number on the d line, respectively. The same is true in the following tables.
In Example 1, the focal length fb (mm), brightness Fno, and imaging range (half angle of view) ω (°) of the second optical system are as follows:
fb=0.75, Fno=1.94, and ω=0 to 30°.
Table 2 shows numerical values of the second optical system in Example 1.
In this embodiment, the first optical system and the second optical system share the image-forming optical system. Therefore, the values of a10 to a19 in Table 1 are equal to those of b10 to b19 in Table 2. The same is true in Examples 2.
The aspherical coefficients and conical coefficients in Example 1 are shown in the following. As described above, the first optical system and the second optical system share the image-forming optical system. Therefore, the values of the a16 surface and the a17 surface are equal to those of the b16 surface and the b17 surface, respectively. The same is true in Examples 2.
A4=2.8000×10−5, K=0.577 a1 surface
A4=−3.000×10−6, K=−0.478 a2 surface
A4=−1.304×10−3
A6=−3.388×10−3
A8=4.371×10−4
A10=−7.611×10−5
K=−0.814 a16 surface
A4=−1.214×10−2
A6=6.983×10−4
A8=−2.812×10−4
A10=1.681×10−5
K=7.287 a17 surface
The values of the formulas (2) to (9) in Example 1 are shown in the following.
fa=1
fb=0.75
f2≧d(f2=12.3, d=3.68)
|f12/fa|=34.4
r2=24.6
r1/r2=0.52
|fb−fa|/|fa|=0.25
bf/fi=1.59
Example 2 is directed to the wide-angle imaging apparatus in
fa=1.00, Fno=2.00, and ω=25 to 90°.
Table 3 shows numerical values of the first optical system in Example 2.
In Example 2, the focal length fb (mm), brightness Fno, and imaging range (half angle of view) ω (°) of the second optical system are as follows:
fb=0.80, Fno=2.00, and ω=0 to 25°.
Table 4 shows numerical values of the second optical system in Example 2.
The aspherical coefficients and conical coefficients in Example 2 are shown in the following.
A4=1.900×10−5
A6=1.037×10−7, K=0.271 a1 surface
A4=−2.000×10−6
A6=−4.713×10−9, K=−0.515 a2 surface
The values of the formulas (2) to (9) in Example 2 are shown in the following.
fa=1
fb=0.80
f2≧d(f2=14.3, d=13.8)
|f12/fa|=15.3
r2=28.5
r1/r2=0.44
|fb−fa|/|fa|=0.20
bf/f1=1.34
In this configuration, the first reflection surfaces 221 have a convex surface as seen from incident light from the object side, and the second reflection surfaces 222 have a concave surface as seen from the incident light. In
In this embodiment, a central axis 253 of the first wide-angle imaging optical system 257 and a central axis 256 of the second wide-angle imaging optical system 258 cross at an angle θ other than 180 degrees. That is, the central axis differs depending on the wide-angle imaging optical system. On the other hand, each of the above embodiments shows an example of θ=180 degrees, which means that the central axis is common to the wide-angle imaging optical systems.
In
Accordingly, when the reflection surfaces formed, e.g., of a glass substrate coated with Al and MgF2 are combined with the refractive optical system and the image-forming optical system that include lenses made, e.g., of Si2AsTe2 or germanium in each of the above embodiments, the reflection surfaces reflect light, and both of the refractive optical system and the image-forming optical system transmit light in a wide range of wavelength regions from visible to infrared. Thus, the apparatus can be used in a wide range of wavelength regions from visible to infrared.
Moreover, when the combination of reflection surfaces and lenses as described in Embodiment 13 is employed, the apparatus can be used in a wide range of wavelength regions from visible to infrared. Thus, surveillance covering a wide range can be performed at any time of day or night, and its condition can be recorded.
An image is formed on the spatial light modulator 292 that is illuminated by a light source 293, and then is magnified and projected by the wide-angle imaging optical system 291 onto the screen 294. Thus, it is possible to achieve a video projector that provides an extremely wide field of view for an observer 295.
A wide-angle imaging apparatus of Embodiment 25 can be mounted on an object, and the mounting angle can be adjusted.
In the example of
When a movable means for changing the mounting angle of the vehicle-mounted imaging apparatus is provided so as to control the mounting angle from the inside of the vehicle 373, the imaging range easily can be changed, and thus the surrounding situation can be detected and recognized precisely.
In this embodiment, the wide-angle imaging apparatus is used as a vehicle-mounted imaging apparatus. However, it is not limited thereto, but also can be used, e.g., as a surveillance imaging apparatus.
Moreover, when the vehicle 394 moves, it is tracked automatically, and the image of the vehicle 394 appears on a wide-area image 411 as a moving object image 412, as shown in
The combination of Embodiments 17, 25, and 26 also can provide highly improved imaging as a wide-angle imaging system that includes a zoom function, an imaging range variable function with inclination, and a moving object sensing function.
As described above, the present invention includes the reflective optical system with the first reflection surface and the second reflection surface, the open portion provided between the first reflection surface and the second reflection surface, the light-transmitting portion provided in the second reflection surface, and the aperture provided in the first reflection surface, thereby producing a panoramic image that covers a wide range, i.e., a maximum horizontal angle of view of 360 degrees and a vertical angle of view of about 180 degrees. Moreover, the main optical system can be composed of reflection surfaces that cause no chromatic aberration. This reduces not only man-hours for design but also constrains on fabrication, so that a small, lightweight, low-cost, and bright wide-angle imaging optical system can be achieved. Therefore, the wide-angle imaging optical system of the present invention is useful for a surveillance imaging apparatus, a vehicle-mounted imaging apparatus, and a projection apparatus.
Number | Date | Country | Kind |
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2001-347568 | Nov 2001 | JP | national |
2002-185199 | Jun 2002 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP02/11817 | 11/13/2002 | WO | 00 | 5/11/2004 |
Publishing Document | Publishing Date | Country | Kind |
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WO03/042743 | 5/22/2003 | WO | A |
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Number | Date | Country | |
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20040264013 A1 | Dec 2004 | US |