How did the multiplane camera create an illusion of depth in Disney animation?

The multiplane camera created an illusion of depth in animation by allowing different layers of artwork to be moved independently at varying speeds and distances from the camera lens.12

By placing foreground, midground, and background elements on separate planes, the camera could simulate the parallax effect observed in the real world, where objects closer to the viewer appear to move faster than those in the distance. This technique, which was instrumental in the production of films like The Old Mill (1937), provided a sense of three-dimensionality and painterly realism that surpassed the flat appearance of traditional animation.2

While Walt Disney is famously associated with the implementation of this technology, his longtime collaborator and technical expert Ub Iwerks was instrumental in its development.12