Cross Polarization in Photography
How to Take Vivid Photos of Plastic Through Polarizing Filters
Aug 22, 2009
Reminiscent of the rainbow-like effects of a puddle of oil, using a polarizing filter allows the photographer not only to see these light effects on pieces of cheap plastic, but also allows her to capture them without post-production.
What is Cross Polarization?
Quite simply, cross polarization (CP) is light traveling between two polarization filters. In this case, the light source has polarizing film placed on/over it and a circular polarizer on the lens. CP has a very valuable application in science as it detects stress in glass and plastic. But, to the photographer, it’s that stress that turns a cheap piece of plastic into an explosion of light.
What You Need
- A Light Source: Your light source should be constant and must be behind the subject for optimal effect. You can use light coming through a window or a light table. In either case, make sure the glass and the film are clean.
- Linear Polarizing Film: This is often the tough part, as this is not readily available. The best way to get this is to order item number PF006 from www.polarization.com. There are other sources out there but, as I found a very reliable source, I haven’t looked any further.
- Circular Polarizer: Any circular polarizer will do. Just find one to fit your favorite lens.
- Plastic Subject: The easiest way to find that perfect piece of plastic is to look at it through your viewfinder after you’ve set up the shot.
- Tripod: A tripod is recommended because, as you rotate the circular polarizer closer to the point where the filter is perpendicular to the reflected light, you will lose a few stops.
Set Up and Shoot
Place your linear polarizing film on/over your light source. Make sure everything is clean and as dust free as possible as dust will break the transmission of light and show up as dark flecks (if shooting for a white background) or white flecks (if shooting for a black background). These flecks can be eliminated in Photoshop but it’s best to start out with as few as possible.
Position your subject directly in front of the light source. With your circular polarizer on your lens, rotate the filter (make sure you’ve focused first) until you get the effect you want. When you look through your view finder, you will see that, by turning your circular polarizer, the light from the table (light source) will go from white through every percentage of gray to black. Play with the circular polarizer AND the position/direction of the objects. Any time any of these items change, your colors change due to the flaws in plastic.
You can also discover whether something is glass or plastic as glass will not present the gorgeous colors like plastic does! This is a technique was used quite often in film cameras for studio work. Keep your post-processing to a minimum as it will actually destroy many of the critical light values. Your shot and colors are set up PRIOR to the shot.
Make it easier! Get a piece of annealed (not tempered) glass and cut the film to fit the glass then tape it to the glass. Tempered glass will show a pattern due to the tempering stresses created to ensure broken pieces of glass are less likely to be dangerous. Now you can take your glass and use it outside, against a window (not polarized or tempered), or any other suitable light source. Make sure to tape all around the edges to keep things clean. Place the laminate facing away from the glass.
Be sure to experiment with different objects as the effects will change based on the thickness and shape of what you’re shooting.
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