The Moon Terminator Illusion, the Dolly Zoom Effect, and Moving vs Zooming

Popular YouTube personality Michael Stevens of VSauce posted this interesting 12-minute video yesterday explaining the optical science behind the “Moon Terminator Illusion” and the “Dolly Zoom Effect” (AKA the Hitchcock zoom).

The Moon Terminator Illusion is when the sunlight hitting the moon doesn’t appear to be coming in a straight line from the Sun — at least from our perspective while looking up at the sky:


The Dolly Zoom Effect, popularized by Hitchcock in his films, keeps a subject at the same relative size in the frame while changing the distance and focal length — what results is a trippy effect that can add drama to a shot:

Stevens explains these two things and other optical phenomena in the video above. At about 7m20s in, Stevens talks about the difference between moving and zooming in on a scene and how the resulting photo/footage differs.

In case you’re interested, here’s a compilation video showing different uses of the Dolly Zoom Effect in film history: