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?
In the middle of the 2000s, the designers at creative consultancy Landor installed Adobe Photoshop on their computers and started using it. General manager Antonio Marazza tells author David Sax:
“Overnight, the quality of their designs seemed to decline. After a few months of this, Landor’s Milan office gave all their designers Moleskine notebooks, and banned the use of Photoshop during the first week’s work on a project. The idea was to let their initial ideas freely blossom on paper, without the inherent bias of the software, before transferring them to the computer later for fine-tuning. It was so successful, this policy remains in place today.”