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Polarized Light Photography eliminates surface reflections and it’s used by professional photographers for high quality documentation of art. The American Institute of Conservation guide to digital photography has in the chapter “Visible Light Photography” a short paragraph on “Polarized Illumination” . This post adds my insights into this method.
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A single particle of light can be imagined as a wave which propagates from its source into space. A beam of light from the sun, an halogen or an LED lamp, is composed of multiple light waves which vibrate in any directions.
When we want polarize this light source we put in front of it a polarizing filter which allows through just the light waves vibrating in one specific direction.
A classical experiment with polarized light is that done with a calcite crystal and a polarizing filter.
Why Polarized light for Art Photography?
Our goal is to eliminate glare in our photos of paintings: in particular, those ugly reflections from varnished paintings. This is the trick: Light from the lamps can be Reflected or Diffused from a painting. Reflected light gives ugly glare while diffused light is pleasant. When the light is reflected it keeps its polarization. When the light is diffused it loses any polarization. So, when we send a polarized light onto the painting, the glare is a polarized beam while diffused light vibrates in any direction.
The final step is to add a polarizing filter on our camera and rotate it 90 degree so to extinguish all reflected light.
See it’s to believe
As usual, we want see some experiments. For this post I used a painting by Domenico Di Mauro, painter of colorful Sicilian traditional carts, currently 99 years young. He still works in his studio which happens to be beside my place. He’s one of the last practicing this craftsmanship.
This is the video:
Polarizing screens. I recommend those from www.polarization.com. They carry the laminated polarizing sheets, width 17″that I use for my Dowel DP 1000 W lamps, I found 1 feet is enough to cover the lamp.
Circular Polarizing filter for the camera. Don’t use a linear polarizing filter for the camera.
Linear Polarizing Filter VS Circular Polarizing Filter
If you do manual focus you can still use a linear polarizing filter. You need a circular polarizing filter when you work in auto focus. Indeed, the focusing system of the camera gets hard time to focus when it receives polarized light. The circular polarizing filter resolves this problem. It is essentially a liner polarizing filter that diffuse the polarized light just before feeding it to the camera.
A video on linear polarizing filter and circular polarizing filter:
References The AIC guide to digital photography and conservation documentation – second edition, Jeffrey Warda editor, American Institute for Conservation, 2012.