Depth of field and the vanishing fence

Abstract

Students are amazed when I show them a zoo photo of an animal behind a fence and then a zoomed-in photo where the fence has disappeared. They ask 'Where did the fence go?' This paper will explore this magical phenomenon which draws from concepts in photography (angle of view, depth of field) and physics (convex lenses, focal length, real images). An accompanying video demonstrates how the fence vanishes as one zooms in on the zoo animal (Ruiz 2018 Video: Where is the fence?