In optics, a caustic is the envelope of light rays reflected or refracted by a curved surface or object, or the projection of that envelope of rays on another surface. The caustic is a curve or surface to which each of the light rays is tangent, defining a boundary of an envelope of rays as a curve of concentrated light.
A piece of milled plexiglass acting as a projecting lens; via the Computer Graphics and Geometry Lab at the École Polytechnique Fédérale de Lausanne
New milling techniques applied to glass and plexiglass panels could be used to “create windows that are also cryptic projectors, summoning ghostly images from sunlight.”
[Pauly and Bompas] hope that the technique will be used in architectural design, to create windows that mould sunlight and throw images or patterns onto walls or floors,” which, if timed, milled, and manipulated just right, could produce a slowly animated sequence of images being projected by an otherwise empty window during different times of day.
To control the shape of a caustic pattern generated by a specular or refractive surface, we need to solve the inverse problem: how can we change the surface geometry, such that incident light is redirected to produce a desired caustic image?
I was thinking about this not long ago while reading in Petapixel an essay by a photographer named Scott Reither, “Long Form Study: Why Photographers Should Repeatedly Revisit A Scene.” In it, he described photographing one particular stretch of beach, over and over, throughout his career.
Of course that landscape has changed over time, and of course he’s had moments when he felt he’d captured the same territory so many times there was nothing left to see.
But there was always something more to see — maybe because of a change in Reither’s life, rather than in the physical environment.