Bring up the Fog window by choosing menu ‘View’->‘Set Fog...’
When AUTO is checked, the fog depth cue (Start and End) automatically recomputes as the camera position changes. This ensures the fog depth cue remains constant as the camera moves in and out of the scene, and saves manual reconfiguration for each camera location. Unchecking AUTO activates the other controls.
Be sure to turn OFF fog in the ‘View’ menu when the camera is located within the sphere.