…the interocular separation of left and right images are created by covering 3 and openings 8 which provides a difocal curviplanar viewing plane in the audience volume.
The term difocal refers to the distance from screen 15 to the observers eyes whereby two interocular points (di) occurring on a curved viewing plane caused by the spacing of openings 8 are of equal (focal) distance so that a complete left and right eye image can be seen by each appropriate eye on said difocal points.
My own use-definition of difocal was this:
Comedy is all about being able to look "difocally" at life. I say difocally, as opposed to bifocally, since bifocals bring two lens-captures into a single optical picture, whereas, let us say, "difocals" keep both lens-captures separate, and thereby require the viewer to view one situation simultaneously under two aspects.
Now, who wants to give me a cookie?