What's Better Than Four Fisheyes?

Considering that NASA uses Nikkors, it's not much of a surprise to see a locomotive use it as well. What is surprising is why they use it:

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.

More:

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.

Wow.