The setup is very simple and it comprises of an approximated front lens element from an 8mm fisheye lens. Because the Octane pinhole camera takes care of focus/fov etc, you only need one lens element to make this work.
When using the Octane plugin, you can parent the camera+lens together which ensures the camera always remains perfectly planar to the lens. In the case of Octane standalone, this is not possible as the camera node is a unique entity which cannot be transformed via connections.
Remember, this is something experimental and not entirely useful because of the several limitations imposed by this approach; render time, focus issues etc.
Enjoy
