Size constancy fails below half a degree.

Size constance is a term used to refer to the fact that objects seem to maintain size as their distance from an observer changes, despite change in image size. It is known that size constancy has limits. People seen from the top of tall buildings look small. By observing objects, including the Moon, and after-images, we demonstrate here that size constancy holds when image size is above half a degree, and breaks down when it is less. In other words, image size is scaled for distance only when image size is above half a degree.