> David Stork, an imaging scientist and former Stanford professor with a side career in computer-aided art analysis, was the major scientific critic of Hockney and Steadman a decade ago. One of his main counterarguments was that, using only a camera obscura, Vermeer would have had to paint upside down and the projected image would be too dim to be useful. Jenison figured out that using a second mirror solves both problems. So in his apparatus, the image is projected through the 4-inch lens onto a 7-inch concave mirror on the opposite wall, and then onto the 2-inch-by-4-inch mirror he’d have right in front of his face as he painted.

https://www.vanityfair.com/culture/2013/11/vermeer-secret-to...