Abstract:
A wide-angle optical system ( 2, 40 ) having an objective ( 4, 42 ) and a mirror system, including a curved mirror ( 6, 46 ) for projecting a wide-angle image through the objective ( 4, 42 ) onto a detector ( 10, 44 ). At least one mirror ( 8, 46 ) of the mirror system is arranged movably relative to the objective ( 4, 42 ). It is possible to achieve a zoom function, a large elevation range and a selection of an enlarged section from the wide-angle image.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention proceeds from a wide-angle optical system having an objective and a mirror system, comprising a curved mirror, for projecting a wide-angle image through the objective onto a detector. 
     2. Discussion of the Prior Art 
     Panoramic cameras or omnidirectional cameras or 360° cameras are known both from the field of robotics for directing mobile robots and from the field of web cameras for Internet conferences. The cameras operate in the visible spectral region and are suitable for distances from a few metres to several metres. Such a panoramic camera is known, for example, from patent U.S. Pat. No. 6,424,377B1. The beam path of the camera is directed via a convexly curved mirror through which it is possible to attain a panoramic view. 
     SUMMARY OF THE INVENTION 
     The invention is based on the object of specifying an improved wide-angle optical system for the purpose of spatial surveillance. 
     This object is achieved by means of a wide-angle optical system of the type mentioned at the beginning and in the case of which according to the invention at least one mirror of the mirror system is arranged movably relative to the object. A movable mirror can be used to project a detail of the wide-angle image in an enlarged fashion. Using a mirror from the mirror system as movable mirror enables additional mirrors to be spared, and the panoramic camera can be kept compact. 
     The mirror system can comprise only the curved mirror, or a number of mirrors. The curved mirror is, in particular, convexly curved and can be, for example, conically, spherically, parabolically or hyperbolically curved. At least one semicircle of the surroundings adjacent to the wide-angle optical system is expediently imaged by means of the wide-angle image projected onto the objective, in particular, the image is a panoramic image or a 360° image with an elevation of at least 40°, expediently between 40° and 90°, and in particular above 100°. The wide-angle optical system is preferably capable of imaging objects arranged opposite the wide-angle optical system. In addition to the curved mirror, the wide-angle optical system advantageously comprises a further mirror, for example, a plane mirror which can be designed in a circular fashion, in particular. The optical beam path of the wide-angle optical system advantageously has only a single effective projection centre. It is possible thereby to reconstruct panoramic images (via cylindrical projection) or perspective images (via plain projection) free from defects via suitable mathematical transformations from omnidirectional images. 
     In a preferred refinement, in addition to the curved mirror the mirror system comprises a flat mirror as movable mirror. The objective or parts of the objective can be arranged together with a sensor inside the curved mirror such that it is possible for the wide-angle optical system to be of small design. 
     In a further refinement, the wide-angle optical system comprises an optical axis running through the objective and the movable mirror. It is possible thereby for the entire wide-angle image, advantageously the panoramic image, to be influenced symmetrically in a simple way by a movement of the movable mirror. 
     If the movable mirror can be tilted relative to the optical axis, a part of the wide-angle image or panoramic image can be singled out selectively and, for example, enlarged. 
     It is expedient that a single or two-fold reflection can be selected for projecting an object onto the objective. In order to project the wide-angle image or panoramic image onto the objective, the beam path from the surroundings of the wide-angle optical system can be reflected by two mirrors of the mirror system, as a result of which it is possible to keep the wide-angle optical system of small design. By reducing the beam path from two-fold reflection to a single reflection in the case of which the beam path is reflected only at one mirror of the optical system, a desired area of the wide-angle image can be projected onto the detector in an enlarged and/or rectified fashion. 
     It is preferred to be able to use the movable mirror to select a beam path which projects an object onto the detector from its surroundings in a way bypassing the curved mirror. A particularly distortion-free projection of an area of the wide-angle image onto the objective can be achieved. The camera objective can be moved parallel to the optical axis for the purpose of focusing (correction of the image). 
     In order to select a desired angular area from the wide-angle image, the movable mirror can advantageously be rotated about the optical axis. 
     The wide-angle image can preferably be zoomed with the aid of the movable mirror, in particular while retaining the azimuth angle of the wide-angle image. Details of the image can be singled out selectively and enlarged. Given a retention of the azimuth angle, the panoramic view of 360° can be retained despite zooming, the elevation range of the wide-angle image being zoomed, and thus the elevation angle being reduced. 
     A zoom function can be achieved in a particularly simple way when the movable mirror can be moved by means of a translation relative to the objective. 
     In an advantageous development of the invention, the curved mirror is movable. It is possible to attain a zoom function with only a single mirror of the mirror system. In this case, the camera objective can be moved parallel to the optical axis for the purpose of focusing (correction of the image). 
     A particularly simple zooming with only a slight, or even without an undesired, displacement of the elevation range of the wide-angle image can be attained by a means for forming the movable mirror. The movement of the mirror relative to the objective can thereby be achieved by the forming of the mirror, or be carried out in addition to a translatory movement, for example. 
     In addition, the invention is directed at a camera system having a wide-angle optical system as described above, a detector and an evaluation unit for processing the wide-angle image projected onto the detector. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantages emerge from the following description of the drawing. Exemplary embodiments of the invention are illustrated in the drawing. The drawing, the description and the claims include numerous features in combination. The person skilled in the art will expediently also consider the features individually and combine them to form rational further combinations. 
       In the drawing: 
         FIG. 1  shows a wide-angle camera having a spherical mirror and a tiltable and displaceable plane mirror, 
         FIG. 2  shows the wide-angle camera from  FIG. 1  with the plane mirror in another position, 
         FIG. 3  shows the wide-angle camera from  FIGS. 1 and 2  with a plane mirror moved in a translatory fashion, 
         FIG. 4  shows a wide-angle camera having a spherical mirror and a plane mirror which can be bent, and 
         FIG. 5  shows a wide-angle camera having a movable spherical mirror. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a wide-angle camera in a schematic way together with a wide-angle optical system  2 . The wide-angle optical system  2  comprises an objective  4  which is illustrated only as one lens for the sake of clarity. The wide-angle optical system  2  also comprises a convexly curved spherical mirror  6  which is transparent within the aperture of the objective  4  such that light can fall onto a detector  10  from a plane mirror  8  through the objective  4 . The spherical mirror  6  is of reflecting design outside the aperture of the objective  4 . In a beam path  12  represented with a continuous line as in  FIG. 1 , a panoramic image from the surroundings of the wide-angle optical system  2  is projected by two mirrors  6 ,  8  onto the detector  10 . 
     As illustrated by a double arrow  14 —the plane mirror  8  can be tilted relative to an optical axis  16  with the aid of a motor  18 , which for the sake of clarity is not illustrated in  FIG. 1 . Such a motor  18  is illustrated by way of example in  FIG. 3 . In order to view a section of the wide-angle image, the plane mirror  8  can be tilted continuously until, for example, it reaches the position illustrated by dashes in  FIG. 1 . As illustrated by a dashed beam path  20 —the result is that this section is projected onto the detector  10 . An elevation angle  22  of the beam path  20  is substantially smaller than an elevation angle  24  of the beam path  12 , for which reason the section is projected onto the detector  10  in a substantially larger fashion by the beam path  20  than by the beam path  12 . 
     The detector  10  is sensitive in the infrared radiation region between 8 μm and 12 μm, and comprises a microbolometer. Connected to the detector  10  is an evaluation unit  26  which comprises a signal-conditioning electronic system for rectifying and correcting the image projected onto the detector  10 , an image- and signal-processing electronic system and also an electronic system for commanding and controlling the movement of the plane mirror  8  and interfaces for integration into a sensor network. 
       FIG. 2  shows the wide-angle optical system  2  with the plane mirror  8  in a somewhat different tilted position. Here, the beam path  20  is directed very closely past the spherical mirror  6 , as a result of which the wide-angle optical system  2  can be used to look a short distance behind the spherical mirror  6 . It is possible thereby to attain a very large overall elevation angle of over 110° for the wide-angle optical system  2 . The scenery of the surroundings arranged a short distance behind the spherical mirror  6  can be projected onto the detector  10  by the beam path  12  only in a very compressed fashion. In the case of a slightly tilted position of the plane mirror  8  as depicted by dashes in  FIG. 2 , this area can be projected onto the detector  10  in a way that is rectified and decompressed. In order to facilitate a panoramic view, the plane mirror  8  can be swivelled about the optical axis  16  by 360° in the direction of the double arrow  28 . The objective  4  can be moved parallel to the optical axis  16  for the purpose of focusing (correction of the image). 
     The translatory mobility of the plane mirror  8  of the wide-angle optical system  2  is illustrated in  FIG. 3 . As shown in FIGS.  1  and  2 —not only can the plane mirror  8  be tilted and rotated about the optical axis  16  by the motor  18 , but—as indicated by a double arrow  30 —it is mounted so that it can be displaced parallel to the optical axis  16 . A zoom function is thereby attained. In the event of a displacement of the plane mirror  8  parallel to the optical axis  16  in the direction of the objective  4 , the beam path  12  represented by continuous lines is displaced into the dashed beam path  20 . The elevation angle  22  of the beam path  20  is thereby smaller than the elevation angle  24  of the beam path  12 , as a result of which the zooming of the wide-angle imaging is attained. However, the elevation angle  22  is not only reduced, but also displaced a short distance upward, the result being that the zoom function is linked to a displacement of the elevation range. 
     In order to keep such a displacement of the elevation range small, or to eliminate it, the plane mirror  8  can be of bendable design, as illustrated in  FIG. 4  in an alternative wide-angle camera. Components substantially unchanged are basically numbered with the same reference numerals. Furthermore, reference may be made as regards unchanged features and functions to the description relating to the exemplary embodiment in  FIGS. 1 to 3 . The following description is restricted in essence to the differences from the exemplary embodiment in  FIGS. 1 to 3 . The plane mirror  8  is of circular design and permanently connected on its outer edge to a support ring  32 . The plane mirror  8  can be displaced parallel to the optical axis  16  with the aid of this support ring  32 . Permanently connected to the circular mirror  8  at its centre is a pulling element  34  with the aid of which the centre region of the mirror  8  can be pulled upwards relative to the support ring  32 , and the mirror  8  can thereby be bent, as is illustrated by dashes in  FIG. 4 . The mirror  8  assumes a parabolic curvature as a result. If—as indicated by arrows  36 —the mirror  8  is displaced upwards together with its support ring  32  and—as indicated by an arrow  38 —is pulled even further upwards by the pulling element  34 , the beam path  12  is displaced from the position shown by continuous lines to the position illustrated by dashes. The elevation angle  24  is thereby reduced to the elevation angle  22 , the elevation range not being displaced in height overall. 
     Another wide-angle camera is shown in  FIG. 5 . The wide-angle camera comprises a wide-angle objective  40  which comprises a single spherical mirror  46  for the purpose of projecting a wide-angle image through an objective  42  onto a detector  44 . In order to produce a zoom function, the spherical mirror  46  can be displaced with the aid of a motor  48  along the optical axis  16  of the wide-angle objective  40 , such as, for example, from the position shown by continuous lines into the position illustrated by dashes. A beam path  50  with an elevation angle  52  is thereby displaced into a beam path  54  with an elevation angle  56 . The elevation angle  56  is smaller than the elevation angle  52 , and zooming of the wide-angle image is thereby attained. The elevation range of the beam path  50  is displaced thereby in a way similar to the case of the wide-angle optical system from  FIG. 3 . 
     The curved mirror  6 ,  46  is illustrated as a spherical mirror in  FIGS. 1 to 5 . Combinations of a plane mirror  8  with cylindrically, parabolically or hyperbolically curved mirrors can also be advantageous for the optical correction of aberrations. 
     
       
         
               
             
               
               
             
           
               
                   
               
               
                 List of reference numerals 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 2 
                 Wide-angle optical system 
               
               
                 4 
                 Objective 
               
               
                 6 
                 Mirror 
               
               
                 8 
                 Mirror 
               
               
                 10 
                 Detector 
               
               
                 12 
                 Beam path 
               
               
                 14 
                 Double arrow 
               
               
                 16 
                 Axis 
               
               
                 18 
                 Motor 
               
               
                 20 
                 Beam path 
               
               
                 22 
                 Elevation angle 
               
               
                 24 
                 Elevation angle 
               
               
                 26 
                 Evaluation unit 
               
               
                 28 
                 Double arrow 
               
               
                 30 
                 Double arrow 
               
               
                 32 
                 Support ring 
               
               
                 34 
                 Pulling element 
               
               
                 36 
                 Arrow 
               
               
                 38 
                 Arrow 
               
               
                 40 
                 Wide-angle optical system 
               
               
                 42 
                 Objective 
               
               
                 44 
                 Detector 
               
               
                 46 
                 Mirror 
               
               
                 48 
                 Motor 
               
               
                 50 
                 Beam path 
               
               
                 52 
                 Elevation angle 
               
               
                 54 
                 Beam path 
               
               
                 56 
                 Elevation angle