A Nephroid Caustic
A caustic is the curve line where all light rays that have been reflected from a curved surface (here the internal surface of a ceramic bowl on a blue paper sheet, and illuminated with sunlight) meet. Fujifilm XH-2, f/11, 1/3 sec, ISO-125, focal length 33 mm (50 mm equivalent on FF).
—Andrea Aiello, Max Planck Institute for the Science of Light, Erlangen, Germany
