The Math and Science of Forced Perspective.
Topics: Java Blog
"Forced perspective" is an in-camera effect (meaning it's done live, on-set, with no computer graphics) which allows filmmakers to create shrinking and enlargement effects. For example, scenes with Gandalf having dinner with the Hobbits in the "Lord of the Rings" movies.
In this video, John Hess from Filmmaker IQ explains the math and science behind this optical illusion.