Using the default camera the focus is the distance(sort of) between the camera and the viewing Plane. Its basically the same as minZ clipping.
If you put a camera at 0,12,0 looking towards Z and place an object at 0,0,0 you end up seeing the object beneath you as the viewing plane is forward of the camera. So if you set the minZ at 0 you end up seeing the clipping. Confusing eh ;) Swap the focus and zoom round f=10 z=100 the fov remains the same, but now the camera will actualy look like its sitting at the position and you wont see the clipping. Or maybe use the Perspective lens, as the viewing plane is default at where the camera is located. Still working my way through the differeces between Papervison and Away, so still lots of guessing :p
