Next time you take a train in Switzerland and go through a tunnel, you can rest assured that the inside walls are in perfect shape thanks to.... five fisheye Nikkor lenses:
This piece of fascinating technology is the front of the diagnostic vehicle for rail infrastructure of the Swiss Federal Railways, which was part of the Innotrans - the international trade fair for rail transportation that took place last week in Berlin, Germany:
Inside the housing, there are five cameras equipped with Nikon DX AF Fisheye-Nikkor 10.5mm f/2.8G ED lenses. The view of the cameras is reflected sideways by 90 degrees using five mirrors mounted on the backside of the front cover. The images from all five cameras are then stitched together into a ring shaped view of the surrounding and is captured as a video stream. Additionally, a 3D-wireframe model is generated in real-time and recorded alongside with the video (it records the closest distance to a object from the apparatus).
The system is used to check the clearance of the track in an automated way - it can detect and document even the smallest deformation in tunnel walls, while driving at full speed. For example: the system has a longitudinal resolution of 7cm (2 3/4 in.) at 200 km/h (125 mph), better at slower speeds, and it can indentify a variety of defects automatically.
The actual product is called T Sight 5000 High performance Clearance Gauge and Tunnel Walls Inspection System and it looks like this:
This is how a portion of the stitched image looks like: