We routinely rely on art to understand science, but science is also used to better understand art. When David Hockney wrote in his book Secret Knowledge that he had "rediscovered" secret methods of the great painters, asserting that "from the early 15th century many Western artists used optics--by which I mean mirrors and lenses (or a combination of the two)--to create living projections," he sparked a debate that would motivate new lines of inquiry and research in a multitude of disciplines including art history, optics, image analysis, and more. Charles Falco later claimed he had proven Hockney's findings scientifically. In the last three "Artful Media" articles, David Stork presented applications of computer imaging for analyzing paintings, some of which challenge those claims. In this article, Falco defends his original findings.