A Tucson physicist and a famed British artist living in Hollywood believe they have broken the code of a 600-year-old puzzle that will transform how the world views the history of art.

        The theory centers on the Great Masters of the early Renaissance, best known for beautiful, lifelike images of people and their surroundings, during an era when art and science had begun to flourish in Europe.

        For painter, draftsman and photographer David Hockney, the portraits from the 15th century also hold a tantalizing secret. After years of studying these artworks, Mr. Hockney was convinced that those artists had covertly used lenses to cast images on canvas to help them capture near-photographic likenesses of their human subjects and scenery as early as 1430.

        This, despite the fact that nothing about the artists using optical devices had ever been recorded, and the known development of such devices was nearly two centuries away.

        University of Arizona physicist Charles Falco, a professor of optical sciences, teamed up with Mr. Hockney last year to apply advanced optics principals to specific paintings, and he discovered evidence that supports the artist's observations.

        “We're not talking about telescopes and microscopes in 1600, but about overhead projectors used by (Jan) van Eyck in 1430, and I can prove it,” Mr. Falco says.
       

Experts take sides

               Some art historians hail the new theory, while others scoff. Critics note the lack of written evidence of such early use of projecting lenses. And the idea negates the towering capabilities of Renaissance artists known to apply mathematics to their craft.

        Phoenix Art Museum's chief curator, Michael Komenecky, is not convinced.

        “This argument seems to minimize and overlook issues of creativity, imagination and artistic license that are all part of these works,” Mr. Komenecky says. “It's possible they used such devices, but they certainly didn't need to.”

        Gary Tinterow, curator of European painting at the Metropolitan Museum in New York, says that although he doesn't buy every conclusion drawn by Mr. Hockney and Mr. Falco, “Hockney is definitely onto something, and he is right to feel that art history has neglected the scientific aspects of technological development.”

        The collaboration between Mr. Hockney and Mr. Falco began after an interview with Mr. Hockney appeared in New Yorker magazine, in which he spoke about his observations.
       

Techniques available

               Mr. Falco brought to Mr. Hockney — a private man who declined to be interviewed — an important concept: what could have served as lenses, long before the development of projection devices.

        Since lens grinding for eye glasses was developed by the early 15th century, an artist could have obtained a lens, set his subject in strong daylight and projected a traceable image on the canvas.

        Mr. Falco believes it's more likely that artists used concave mirrors. Holding a 2-inch concave shaving mirror, Mr. Falco showed how an image could be projected, inverted but not reversed.

        The artist could have sat facing his subject with the mirror placed discreetly just behind him. The image would be projected on the canvas, unseen by the subject, allowing the artist to trace the upside-down image. Later, after the subject was gone, the canvas could be inverted and paint applied.

        “Circumstantial evidence points to the mirror being used,” Mr. Falco says.
       

Focused evidence

               Using precise measurements, mathematics formula and a broad understanding of optical phenomena, Mr. Falco zeroed in on several bits of evidence:

        • Areas that seem out of focus, denoting the limited depth-of-field of a lens.

        • Vanishing points that switch with precise consistency, signifying that the position of a lens had been changed during tracing.

        • Unexplainable consistencies of size and technique of works by various, far-flung artists, which Mr. Falco says are the result of limitations of the rudimentary lenses that were widely used.

        • Uncanny precision in copying tiny detail.

        Under Mr. Hockney's guidance, Mr. Falco looked at paintings by such early Renaissance artists as van Eyck, Rogier van der Weyden, Anthonis Mor and Lorenzo Lotto.

        In May, Mr. Falco and Mr. Hockney presented a symposium on their work-in-progress to artists and art historians at the National Gallery in Washington. Mr. Hockney and Mr. Falco published their findings in a scientific journal, Optic and Photonics News.

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