1. A lens, comprising: an outer radius r l having a separating facet, wherein r l is approximately equal to r c * tan ( fov c 2 ) cos ( fov l 2 ) * tan ( fov c 2 ) - sin ( fov l 2 ) , wherein r c comprises a distance from a center of rotation to an image-acquisition plane, and wherein fov c comprises an effective horizontal field of view for the image-acquisition plane, and fov l comprises an effective horizontal field of view spanned by the lens, and wherein left- and right-eye rays received by all separating facets of the lens and passing through a lens-surface-intersection point located at the outer radius r l are tangential to a circular path of eye rotation.