(Courtesy Charles M. Falco, David Hockney)

This photo from a publication of David Hockney shows a an optical setup.

Friday  would have been the Dutch master Rembrandt’s 410th birthday, which makes it seem like a good time to look at the somewhat controversial issue of how he painted.

The British artist David Hockney and University of Arizona Optical Sciences and physics professor Charles Falco have developed a theory that Rembrandt, and several of his contemporaries, used mirrors and other lenses in their painting.

What has become known as the Hockney-Falco Thesis?

These artists projected images on a canvas to reproduce specific aspects of a painting with great detail.

"If you thought somebody like Rembrandt was a genius,  you actually underestimated him," Falco said.