Split Diopter

A diopter is a filter that works similar to a magnifying glass, making a lens focus closer. A split diopter has it on only one side, meaning that one side focuses close and the other farther away. This allows objects at different distances from the camera (usually on the left and right side of the screen) to be in focus simultaneously. Used to great effect in The Thing, for example, where dark sets disguised the blurred region in the middle of the split shot. Sometimes used by first time directors as a way to "show off" their technical skills.

Examples:
 * Equilibrium
 * The Last Castle
 * Heroes
 * Many films by Brian De Palma.