In a previous post we looked at the fun trick of optics is called caustics, where undulating waves act like lenses to cause a network of dancing lines on the sea floor. That’s called a caustic projection.
The same kind of thing happens when light bounces up from the water surface. It’s called a caustic reflection. It’s a common sight on the sides of docked sailboats or on the undersides of bridges in Venice.
In this case the caustic lines are fairly parallel to each other because the waves are, too. The light is hitting the water at a low angle (allowing a greater amount of light to be reflected upward), and the caustic reflections spread out and go a little out focus on the near side of the bridge.
A caustic pattern appears on the inside surface of the vaulted arch in this painting from Dinotopia: Journey to Chandara.
This figure shows how the two kinds of caustics work. The waves act like curving mirrors and lenses at the same time.
Photo by imappi2 on Flickr
Previously on GJ: Caustic Projections