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?
Ugh, now I have to write this boring part, I would think. I would spend a few days in active rebellion against this directive that I imagined the book was imposing.
Then I would realize: this is my book! There are no rules! I can write it however I want! Also, I would think, if I’m bored by something that I believe I need to write, the reader undoubtedly will be too, if not because the subject is inherently boring, then because I myself find it so unbearably tedious to imagine discussing it for five pages. Often as not, I would remember some aspect of the subject that deeply interested me, something a little outside the way it’s usually perceived or written about. Then I would meditate on that, and soon I would be scribbling notes from an increasingly excited place until I found a way forward. A form of beginner’s mind.