University of Arizona professor uses an SLR to examine paintings in the infrared

Charles M. Falco's inexpensive, modified digital SLR camera has thrilled art conservators with what it can do at infrared wavelengths.

By Lori Stiles, University Communications

December 4, 2009

[edited from article at University of Arizona news]

A scientist at the University of Arizona in Tucson has modified a commercial 8-megapixel digital SLR camera for infrared use, creating an inexpensive, portable new tool that even amateur photographers can use to quickly see through layers of paint in artwork to reveal drawings, defects or other features on the original canvas.

Conservators have been using infrared, or IR, cameras to examine and document artwork since the late 1960s. "But these cameras can cost upwards of $100,000, so the number of paintings studied by this technique has been extremely limited," said UA optical sciences and physics Professor Charles M. Falco.

‘The technique is based on the fact that many common pigments are partially transparent to infrared light, making it possible to use appropriate infrared sensors to capture important information from surfaces that are covered by layers of paint," he said.

Early last year, Falco – an experimental physicist who has been interested in photography and in art since childhood – had an idea that he thought might work

He realized that modern digital cameras use silicon sensors sensitive to the germane infrared wavelengths and that such cameras might be modified to capture high-resolution infrared photographs – or "IR reflectograms" – of works of art.

Falco bought a one-generation-old Canon 30D camera on eBay.

"If this didn't work, I would have been out the better part of $1,000. But I was willing to accept that," he said.

For about another $450, Falco converted the camera by removing the infrared-blocking filter and replacing it with a visible-blocking filter, thereby allowing only IR light to reach the camera's sensor. He also adjusted the electronics so that the autofocus feature automatically offsets the camera lens to bring infrared light into sharp focus.

Then he began visiting museums to photograph art.

In a little over a year, Falco has tested his system under a variety of conditions in a dozen museums on three continents, including the National Gallery of Art in Washington, D.C., the State Hermitage Museum in St. Petersburg, Russia, and the National Museum of Western Art in Toyko, Japan.

The first paintings Falco studied were in the Samuel H. Kress Collection at the University of Arizona Museum of Art. Among these works is a painting titled "The Man of Sorrows with Saints and Donors." It was painted by an unknown French artist, probably sometime between the years 1525 and 1550.

"My camera let me discover something about that painting that nobody knew existed - that there are guide lines under the paint that the artist used to create the pedestal in perfect perspective," Falco said. "These lines reveal that this Early Renaissance artist understood and based his drawing on the constructed laws of perspective."

Falco's converted camera, including its 35mm f/2 lens purchased for less than $250, cost about $2,000 total.

Editors of the "Review of Scientific Instruments" invited Falco to write a technical description of his high-resolution imaging instrument and published the paper as the cover story of their July 2009 issue. The paper, titled "High resolution digital camera for infrared reflectography" is published online.