Could a lens be used to help artists make copies of their paintings?
Indeed a lens can. In fact, the identical optical setup is used for projecting a two-dimensional painting as for a three-dimensional person or object. The sub-millimeter accuracy with which van Eyck’s painting of Cardinal Albergati reproduces his 40%-smaller drawing provides very strong evidence that van Eyck used a lens to aid him in making this painting by enlarging the drawing by means of a projection. Evidence of van Eyck’s use of optics is contained in other of his paintings as well. Van Eyck’s drawing of Cardinal Albergati is ~40% smaller than his painting. However, as shown when you roll your cursor over the detail at the right below, when we enlarge the drawing and overlay it on the painting, the correspondence between the major features (eyes, nose, mouth, etc.) as well as the minor details (wrinkles, lines, creases, etc.) within each of the three large regions outlined above is to a precision of better than 1 mm, providing strong evidence that van Eyck used a lens as a tool.
