-Now consider a focal length ratio of 4 (figure 5). As expected, the angle
-$\alpha$ is smaller still. The dotted square is the bounding square of
-the phantom rotated by 45 degrees, corresponding to the geometry of a
-projection taken at that angle. Note that the fan beam now clips the top
-and bottom corners of the bounding square. This illustrates that one may
-still be clipping the phantom, despite \ctsim\'s best efforts. You have
-been warned.