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Make cross-polarised art
Techniques
24 October 2007 14:29
Getting wild, wacky and colourful still life shots without expensive lighting kits or hours of clever Photoshop trickery is relatively easy. All you’ll need to get started is a tripod, two cheap polarising filters, a desk lamp, a sheet of frosted glass and a few plastic props.
This cross-polarisation technique has its roots in the engineering industry, where it’s used to investigate structural stresses, but you can use the same methods to produce some intriguing colourful images.
When it comes to choosing subjects, clear or slightly opaque plastics are the best. We tried a variety of objects from the classic ruler and CD cases to a case from a CompactFlash card. But don’t stop there: every home will be full of plastic objects to try. The more you search and experiment, the better you’ll do.
When shooting with any indoor light source you need to consider the colour of the light. Technically you should choose the correct white balance on your digital camera or add a colour correction filter to suit the light. But a technically correct image isn’t always the best option. Despite using a tungsten light, our most effective images were shot using daylight colour balance or on Fuji Velvia 100 slide film. The orange colour cast only added to the impact of the shots. While we’re on the subject of film, you’ll find that colour slide films give the most dramatic effects, as most processing laboratories will try to correct the colour of your prints if you shoot on negative film.
Polarising filters work by only allowing light into the lens through a single plane. It helps to think of light like waves. Before polarisation, the light travels in all directions, with the filter only letting through the light that is travelling in the same direction. A second polarising filter has the same effect, so if it’s in the same orientation it will let all the light through. Turn this filter through 90 degrees and it will block all of the polarised light from the first filter.
Putting a plastic object between the two filters shifts the orientation of the light passing through it, so this light isn’t stopped by the second filter and gives you the spectrum of colours you see when you rotate the filter on the camera.
The key is to have two polarising filters – one on the light source and another on the camera lens. For studio flash units or lightboxes try the polarising gels from Lee Filters (£70, 01264 355919, www.leefilters.com). Using a smaller light source such as a desk lamp, you can get away with using a smaller polarising filter such as a Cokin A-series polariser (£18, Intro 2020, 01628 674411, www.intro2020.co.uk). Whichever light you choose needs to be positioned directly behind the subject for best effect, with opaque or frosted glass between it and the subject to help diffuse the light.
For small objects you’ll need a lens or camera that will focus close enough to fill the frame. A standard zoom will be fine for larger subjects. If you’re using an automatic camera, make sure the polariser fitted to it is a circular type in order for the metering to work correctly.
Remember that when metering for a backlit subject, the built-in meter can be fooled into giving the wrong exposure. If the background of your subject is still bright after rotating the polarising filter on the lens you may need to add an extra stop of exposure compensation.