Vashi Nedomansky and I joke around a lot about split diopters on Twitter, so it's time for some real talk. Shoved smack in the middle of a traditional Hollywood narrative film, they're jarring and bizarre. And the best use cases for split diopters take advantage of this. Out of context and as a still frame, this split diopter shot from "Patriot Games" (1992) seems utterly ridiculous.
"Two planes of sharpness? The only shot in the movie where this happens? Puh-leeze. It's a trick shot. The cinematographer is just showing off, whatever."
But here's the shot in context. Ryan is desperately trying to piece together fragments of his memory from the traumatic event that opened the film. The split diopter shot is from the point of view of his memory, not an omniscient, objective observer. It's supposed to be weird.
The bizarre visual nature of the split diopter feels right at home for a dream sequence, or a personal flashback moment--the shot is literally Ryan's POV as he's visually searching his memories for details, looking for evidence. An innovative use of the split focus shot.