The 3D background is not completely effective at removing the dizziness factor. I suggest a new PREZI feature to zoom a frame to 80% of the field of view instead of zooming the background. This will remove the dizzies. The zoom percent could be an editable property of a frame.
Frame of reference acts on a viewer’s sense of physical movement. For example, you can make yourself dizzy by turning your head left then right so see what’s there, but you will not get dizzy if you keep your head still and move your eyes. Although the main cause of dizziness is the movement of fluids in your ear while turning your head, you can trick your brain into the same dizziness by moving the background.
Notice your reaction to a 3D background. It causes less dizziness because the background is not moving as much. The zoom is a combination of zooming the 3D background while only slightly zooming the main background.