fig1 shows a first exemplary navigation system 1 in accordance with the invention , wherein the navigation system 1 is coupled to an optical camera comprising two individual cameras 4 a and 4 b , which are part of an optical tracking system 2 and are describe din more detail below . the navigation system 1 can be connected to the optical tracking system 2 by means of a data line , such as for example a cable 3 , or via radio . the cameras 4 a and 4 b can detect infrared light signals emitted or reflected by markers ( e . g ., the three markers of the reference star 6 ) so as to detect a position of the medical instrument 5 ( shown as a pair of scissors ) connected to the reference star 6 . each of the cameras 4 a and 4 b also can be used as a video camera , wherein visible light is detected . the data of the reference star 6 , detected by the optical tracking system 2 in the infrared mode of the cameras 4 a and 4 b , can be transmitted to the computational unit 1 , together with the data of the instrument 5 detected in the video camera mode , and for example evaluated as described in ep 1 667 067 a1 by referring to fig3 and 4 in ep 1 667 067 a1 . by integrating the video camera function into the optical infrared tracking system , the step of calculating the current position of the video cameras in space is omitted . thus , an instrument 5 , which , for example , may be pre - calibrated , can be tested or verified by correlating the images recorded by the cameras 4 a and 4 b in the infrared range for detecting the markers and in the visible range for detecting the shape or geometry of the instrument 5 . this data can be used to determine if there is a deviation of the instrument from a predetermined shape of the instrument . calibrating the video cameras , for example when manufacturing the system , provides the information for a “ virtual camera ”. this information remains valid , since the position of the video camera relative to the tracking system is not changed after calibration . if another , detached video camera 4 c is provided , as shown in fig2 , then the current position of the camera 4 c also can be determined so as to relate the position of the tracked instrument 5 to the “ virtual camera ”. fig2 shows a second embodiment , wherein another camera 4 c is detached from the optical tracking system 2 ( which includes the cameras 4 a and 4 b ). the camera 4 c can be connected to the computational unit 1 via a separate data connection , such as for example a cable 3 a . such an arrangement enables detection of the instrument 5 to be more flexibly configured using the additional camera 4 c , since the latter can be positioned independent of the tracking system 2 . this can enable easy detection of the instrument 5 from a number of directions . to this end , the distance , starting from the coordinate system of the additional camera 4 c , between the instrument 5 and the camera 4 c can be ascertained . this enables evaluation of the image data detected by the camera 4 c such that dimensions or the geometry of the instrument 5 can be ascertained from the data . a spatial location of the camera 4 c , via its connection reference star 6 a ( which is detectable by the tracking system 2 ) can be calculated . from the spatial position of the additional camera 4 c , the relative position between the camera 4 c and the instrument 5 also can be calculated . thus , the distance between the instrument 5 and the video cameras can be determined . it is thus for example possible to calibrate an instrument by means of three cameras 4 a , 4 b and 4 c , which can respectively detect infrared and visible light . fig3 shows a perspective cross - sectional view of a camera 4 , wherein in the incident light region of the camera 4 , a lens 8 is shown as an example of a lens system and is surrounded by leds 9 a and 9 b . the leds 9 a and 9 b , for example , can be arranged annularly around the lens 8 as shown in fig5 . a beam of light entering through the lens system or lens 8 impinges on a semi - transparent mirror 7 , which lets through a portion of the beam of light so as to strike both the filter 5 b lying directly in the beam path and the detection element or ccd element 6 b lying behind it . by means of the ccd element 6 b , light can be detected in the wavelength range which the filter 5 b lets through . a portion of the light entering through the lens 8 also may be reflected by the semi - transparent mirror 7 in the direction of the second filter 5 a , which lets through light in a different wavelength range relative to the filter 5 b . the light of said other wavelength range strikes the second ccd element 6 a lying behind the filter 5 a in the direction of the beam of light reflected by the semi - transparent mirror 7 , wherein said ccd element 6 a can detect in said other wavelength range . the wavelength range that is detected , sequentially or also simultaneously , by the ccd elements 6 a and / or 6 b can be set , depending on the type of filters 5 a and 5 b that are used . it may be noted that one of the filters 5 a and 5 b can be omitted in the example embodiment shown in fig3 . this can be done , for example , to detect visible light by means of the ccd element not shielded by a filter , wherein an infrared filter , for example , can be placed in front of the other ccd element . the region in front of the camera 4 , for example , can be illuminated with infrared light by means of a light source 9 a . this can improve the detection of reflective markers . the second light source 9 b , for example , can emit light in another wavelength range , such as for example visible light or also ultraviolet light , so as to improve the detection of objects using light in the visible range . however , depending on the application , it is also possible to omit one or all of the illuminating elements 9 . it may be noted that the position of the ccd elements 6 a and 6 b in relation to the semi - transparent mirror 7 can be different . for example , the ccd elements 6 a and 6 b can be at different distances from the mirror 7 , since light of different wavelengths does not focus onto exactly the same point . the optical element 8 can also be configured to be variable , in a similar way for example to a photographic or video camera such as is known in its own right , in order to focus the light on the respective sensor 6 a or 6 b , depending on the desired light detection range . fig4 shows a second embodiment of a camera 4 in accordance with the invention , wherein a beam splitting prism 10 is provided instead of the semi - transparent mirror 7 shown in fig3 . light 11 entering the prism 10 is split into light of a first wavelength range 12 b , which passes through the prism 10 and strikes the first ccd element 6 b . light of a second wavelength range can be refracted by the prism 10 and deflected onto the second ccd element 6 a as diverted light 12 a . it is thus also possible to omit filters and simultaneously , for example continuously , detect an object using the two ccd elements 6 a and 6 b . fig5 shows an exemplary stereoscopic camera , wherein two individual cameras 4 a and 4 b are separated from one another , for example as described above , are arranged in a casing 13 . the respective lenses 8 and the illuminating elements or leds 9 can be seen in the perspective shown in fig5 . a cpu 14 can be arranged in the casing 13 and connected to each of the cameras 4 a and 4 b and , in particular , to the respective ccd elements 6 a and 6 b . via a connection 3 , stereoscopic images detected by the cameras 4 a and 4 b can be transmitted in two different wavelength ranges to the computational unit 1 shown in fig1 and 2 . recording the images using the cameras 4 a and 4 b , setting the lens system 8 or setting or positioning a filter 5 a and 5 b , such as for example shifting a filter in front of one or more of the ccd elements 6 a and 6 b in order to detect a different wavelength range , can be controlled by means of the computational unit or cpu 14 . the cpu 14 also can synchronize the ccd elements 6 a and 6 b of a camera and the illuminating elements 9 a and 9 b respectively assigned to the respective ccd elements 6 a and 6 b . the evaluation result or also the optical signals , which for example may not be directly evaluated by the cpu 14 , can be transmitted to another system via the connection 3 . although the invention has been shown and described with respect to a certain preferred embodiment or embodiments , it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings . in particular regard to the various functions performed by the above described elements ( components , assemblies , devices , compositions , etc . ), the terms ( including a reference to a “ means ”) used to describe such elements are intended to correspond , unless otherwise indicated , to any element which performs the specified function of the described element ( i . e ., that is functionally equivalent ), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments of the invention . in addition , while a particular feature of the invention may have been described above with respect to only one or more of several illustrated embodiments , such feature may be combined with one or more other features of the other embodiments , as may be desired and advantageous for any given or particular application .
a camera system includes at least two camera units , wherein each camera unit comprises at least one detection element for detecting an optical signal . at least one of the at least two camera units includes at least one element operative to enable detection of light in at least two different spectral ranges .