SFX Secrets: The Split Diopter Lens
If you've seen Brian de Palma's Carrie or Blow Out, it’s likely that you’ve seen the split focus shot. The director popularized the use of the split diopter lens in the ’70s and ’80s, although it was used by Gregg Toland as early as the ’40s in Orson Welles’ Citizen Kane. Similar to deep focus, the effect is achieved by using a split diopter convex lens resulting in objects in the background and foreground to be equally in focus.