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?
A young man named Michelangelo stands in front of a huge granite monolith. He stands there at a time in history before the technologies that brought us the hammer and chisel have occurred. He gazes at the rock. He dreams his dream and the best that he is able to say is, What a wonderful stone you are.
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Michaelangelo now stands in front of the same rock. Thrust into his hands are a hammer in one and a chisel in the other. He looks at his hands, at the technological tools that they hold, and gazing at the same stone, with epiphanic zeal, says I must let Moses out.