WO2004066013A1 - Catadioptric camera - Google Patents

Abstract

Disclosed is a catadioptric camera comprising an image plane, an optical axis (1), a main optical system which is provided with at least one mirror (7) that is placed on the optical axis and blocks the view from the image plane to a dead area located behind the mirror (7), and an auxiliary optical system (13, 14) which extends through a window (11) of the first mirror (7) and projects at least one portion (17) of the dead area (16) onto the image plane.

Description

 Catadiσptric camera

The present invention relates to a catadioptric camera, that is to say a camera in which not only lenses but also curved mirror surfaces are used as imaging elements.

Conventional lenses in lens optics record images from a conical observation space, at the apex of which the lens is located. Most lens optics are designed for cone opening angles or viewing angles of no more than 90 °. Although larger viewing angles can be achieved, this requires considerable technical effort. In order to achieve a uniform brightness of an image produced by such a lens, care must be taken that light that strikes the lens from an edge region of the observation cone also hits the front lens at a not too large angle. The resulting bulging shape of the front lens has given such lenses the designation "fish eye". The risk of damage is high with such a bulging front lens. Viewing angles of the order of 180 ° or above cannot be achieved with conventional lens optics.

For surveillance tasks, there is a need for imaging systems that are able to monitor as large a field of view as possible with a lens or in which the imaging surfaces are better protected than in one This object can be achieved with so-called catadioptric lenses, in which curved mirrors form at least part of the optical system. Lenses of this type are known, for example, from WO 00/41024, US 6 392 687 B1 and US 633 826 B1 eg US Pat. No. 6,392,687 B1 a cathodic camera in which a lens system is accommodated inside a mirror referred to as the main reflector, a front lens of this lens system being inserted into an opening of the main reflector and observing an opposing second reflector, the one with the latter The cone-shaped space that can be observed by the camera has an opening angle of significantly more than 180 °, but within this field of view there is a dead area in which the second reflector blocks a view of the lens system straight ahead, but this was not perceived as annoying, since essentially one Application of the camera with a vertically oriented optical axis was thought In such a setup, the camera has a 360 ° horizontal view, and the dead area is oriented toward the zenith or nadir, in a direction that is generally of less interest to observe.

The need to orient the optical axis essentially vertically, however, undesirably limits the field of application of such a camera. In principle, for example, it would be conceivable to use such cameras on motor vehicles, for example for stereoscopic distance measurement to a vehicle in front, as an aid when parking and the like. However, there are hardly any horizontal surfaces available on a motor vehicle on which such a camera could be mounted. If you mount such a camera with a vertical optical axis on a non-horizontal surface, the surface itself blocks a large part of the field of view of the camera, and if you mount the camera with an optical axis perpendicular to the surface, you run the risk that a spatial area, that should be observed falling into the dead area of the camera. The object of the invention is therefore to provide a catadioptric camera in which the dead area, if not completely eliminated, is at least substantially reduced.

The object is achieved by a camera with the features of claim 1. The fact that part of the surface of the first mirror opposite the image plane corresponds to the dead area and which does not contribute to the creation of an image of the surroundings, but at most of is used by the camera light coming from the image plane is reflected back to it. By providing a window in this area of the first mirror, the imaging properties of the main optical system are not changed, but a clear view from the image plane is created into the dead area covered by the first mirror.

The optical auxiliary system is preferably designed as a lens system. Its viewing angle can correspond exactly to the opening angle of the blind area of the main optical system. If this is the case, the dead area is reduced to a hollow cone with a wall thickness which corresponds approximately to the radius of the first mirror. Such a remaining dead area is negligible if the objects to be observed are at a distance from the camera that is a multiple of the radius of the first mirror.

For special applications and in particular for observations in the near field, it can be expedient if the viewing angle of the auxiliary system is slightly larger than the opening angle of the blind area. In this case, the observation areas of the main system and the auxiliary system overlap at a great distance from the camera, but there is one level where the observation areas seamlessly adjoin each other. The greater the difference in the opening angle of the dead area, the smaller the distance of this plane from the camera of the main optical system and the observation area of the auxiliary system.

The blind spot of the main optical system or the surface area of the first mirror replaced by the window in accordance with the invention corresponds to a conical volume between the first mirror and the image plane through which no light beam contributing to image generation passes. In the article "Real-Time Target Localization and Tracking by N-Ocular Stereo", T. Sogo et al., Proceedings of IEEE Workshop on Omnidirectional Vision, Hilton Head Island, SC, USA, June 12, 2000, "A camera is presented which has a blackened cone in this volume, which serves to suppress highlights and multiple reflections in the image generated by the camera. In the already mentioned US Pat. No. 6,333,826, one is used in this volume between the front lens. ***" of a lens system and a pin attached to the second mirror as a support for the second mirror. According to the present invention, this pin is preferably replaced by a tube through which the beam path of the auxiliary system runs It also considerably simplifies the construction of the optical auxiliary system, since it enables lenses of the auxiliary system to be placed anywhere along the op table axis between the first mirror and the image plane.

The camera preferably also comprises a second mirror, which is located upstream of the first mirror in the beam path of the main optical system. These two mirrors can be permanently and permanently connected by a transparent dome, which also forms an entry window for the main optical system. It is also conceivable that the two mirrors are surfaces of a single transparent body, in which case the tube, if present, is formed by an axial bore in the transparent body. Further features and advantages of the invention result from the following description of exemplary embodiments of the invention with reference to the attached figures.

Show:

1 shows a section along the optical axis through a catadioptric camera according to a first embodiment of the invention;

FIG. 2 shows a section analogous to that of FIG. 1 through a variant of this camera;

3 shows a schematic section through a camera according to a second embodiment of the invention; and

4 and 5 two variants of the ratio of the dead area of the main system to the observation area of the auxiliary system.

1 shows a schematic section through a catadioptric camera according to a first embodiment of the invention. The camera comprises a cup-like housing 1 with a light-sensitive element arranged on the optical axis A, such as a CCD (Charge Coupled Device) 2. The top of the housing is closed by a convex carrier body 3 made of glass, a dimensionally stable plastic or the like , The carrier body 3 carries on the outside a mirror 4, e.g. in the form of a vapor-deposited, possibly tempered aluminum or silver layer. A central bore 5 of the carrier body 3, through which light falls on the light-sensitive element 2, extends along the optical axis A.

Opposite the CCD 2 and the mirror 4 is another carrier body 6, on the underside thereof in the same way as in Carrier body 3 a mirror 7 is formed. The two carrier bodies 3, 6 are rigidly connected by a transparent dome 8, which at the same time forms an entry window of the main optical system of the camera. This main optical system comprises the two mirrors 4, 7 and possibly a lens or a lens system (not shown), which can be attached in the bore 5 in order to possibly. Correcting aberrations of the mirror.

The figure shows the course of two beams 9, 10, each of which designates the limits of the region observable with the main optical system. The main optical system draws a ring-shaped image of this observable area on the CCD 2, the dead area covered by the mirror 7 corresponding to a central dark zone in the interior of the ring.

A window 11 is formed in the mirror 7 and its support body 6 on the optical axis A. The window does not influence the imaging properties of the main optical system, since it is in a blind spot at which the CCD 2 would only see its own mirror image if the mirror 7 were continuous there. A tubular tube 12 is inserted into the window 11. The tube is black on the outside to intercept stray light in the space between the mirrors 4, 7, which could otherwise cause annoying highlights on the CCD 2. A plurality of lenses 13, 14 are anchored in the interior of the tube 12, which - if present, together with lenses mounted in the bore 5 - form a lens objective. This lens objective projects an image of its observation space into the dark spot in the middle of the ring that is not illuminated by the main optical system. The opening angle of the field of view is exactly the same as that of the blind area of the main optical system. Figure 4 illustrates this relationship. The dead area 16 of the main optical system and the observation area 17 of the auxiliary optical system formed by the lens lens are two around optical axis A centered cone with the same opening angle. There is an area that is neither observable with the main system nor with the auxiliary system in the form of a hollow cone with a wall thickness that corresponds approximately to the difference between the radii of the mirror 7 and the front lens 13 of the lens objective. In practice, this wall thickness is a maximum of a few centimeters and can therefore usually be neglected when it comes to detecting objects of at least several centimeters in size at a distance of approximately one meter or more.

As FIG. 5 shows, the opening angle of the observation area of the auxiliary optical system can also be chosen to be larger than that of the blind area of the main optical system. If this is the case, there is a plane 18 perpendicular to the optical axis A, in which the observation areas of the main system and the auxiliary system merge seamlessly into one another. Beyond this level 18, the observation areas partially overlap, so that one and the same observed object can be imaged twice on the CCD 2, once in the ring illuminated by the main system and once in the central spot illuminated by the auxiliary system. Since the overlap of the observation areas increases with increasing distance from the camera, the arrangement shown in FIG. 5 is less suitable when it comes to monitoring objects at a great distance; for monitoring close to the camera, e.g. If a camera according to the invention mounted on a bumper of a motor vehicle is used to monitor any obstacles when parking, the reduction in the remaining dead area achieved in this way is advantageous.

Of course, it is also conceivable to use a lens with a variable focal length for the auxiliary optical system, which lens is used to monitor the far range for an observation that corresponds to the blind spot of the main system. angle and for monitoring the close range can be set to a larger observation angle.

1, the front lens 13 of the auxiliary optical system is inserted directly into the opening of the window. This limits the light intensity of the auxiliary optical system and can lead to the image generated by the auxiliary optical system being undesirably darker than that of the main system. In the embodiment of FIG. 2, this is avoided by using a front lens 13, the diameter of which is considerably larger than that of the window 11 and which accordingly gives the lens a higher light intensity.

3, the two carrier bodies 3, 6 and the dome 8 are replaced by a single glass body 20, which has a substantially conical, possibly anti-reflective coated outer surface, which forms the entry window of the main optical system, and two mirrored ones Has outer surfaces that form the mirrors 4 and 7, respectively. Here too, a window 11 is provided in the area of the blind spot of the mirror 4, through which the optical auxiliary system runs. However, with this configuration, the tube of the optical auxiliary system is not formed by a tube anchored to the mirror 7, but by a recess 21 of the glass body 20 running along the optical axis A. The side walls of the recess 21 can be blackened, like the tube tube 1 to intercept stray light in the space between the mirrors, and the tapering of the tube in the direction of the CCD 2 is preferably formed by one or more shoulders, which at the same time act as a support for lenses inserted from the open end of the recess 21 of the optical auxiliary system can serve.

Claims

DaimlerChrysler AG patent claims 1. Catadioptric camera with an image plane, an optical axis (1) and at least one first mirror (7) arranged on the optical axis, which blocks the view from the image plane to a dead area lying behind the mirror (7), characterized in that the camera has a main optical system (4, 7) to which the first mirror (7) belongs and an auxiliary optical system (13, 14) which extends through a window of the first mirror and at least a part (17) of the dead one Area (16) maps to the image plane. 2. A catadioptric camera as claimed in claim 1, that the optical auxiliary system (13, 14) is a lens system. 3. Catadioptric camera according to claim 1 or 2, and that the auxiliary system (13, 14) has a viewing angle that corresponds exactly to the opening angle of the dead area (16). 4. Catadioptric camera according to claim 1 or 2, characterized in that the auxiliary system (13, 14) has a viewing angle, which is slightly larger than the opening angle of the dead area (16). Catadioptric camera according to one of the preceding claims, so that the beam path of the auxiliary system (13, 14) runs through a tube (12, 21) which extends from the first mirror (4) in the direction of the image plane. Catadioptric camera according to claim 5, so that at least one lens (13, 14) of the auxiliary system is held in the tube (12, 21). 7. The catadioptric camera according to one of the preceding claims, that it comprises a second mirror (4) which is arranged in front of the first mirror (7) in the beam path of the main optical system (4, 7). 8. Catadioptric camera according to claim 7, so that the two mirrors (4, 7) are connected by a transparent dome (8) which simultaneously forms an entry window of the main optical system. 9. Catadioptric camera according to claim 7, so that the two mirrors (4, 7) are surfaces of a single transparent body (20).