Lighting, a big part of the job.

"And what of the glare from my light source? Can I just get the glassy spherical thing out of the way?"

"On the second part of your question no, it serves a pivotal focusing role. We do have a clever trick though. Something Orson Welles used in the making of Citizen Kane."

He went on to describe masking and depth-of-focus. A mask at one focal plane need not mask at another. Because of the bending at the surface just described the two planes were quite distant from each other and an excellent application for the idea behind "deep focus".

Once again, this pattern (I hesitate to call it a design pattern, implying a designer which may or may not be the case) has its corollary somewhere past the other ramp to the identity bridge. Fields best describe propagation on both ends when 'viewed' this way.

Orson Welles seminal work in cinema served, on many levels, as inspiration for the decode - depth, the critical dimension.