What we don't see all around us
Chatting with some camera club members today brought up the idea of making images of the crystals that form when solutions of something evaporate. The effect is similar to frost forming on a window but the shape of the crystals is different depending on what chemical you dissolve in the water and how fast it evaporates. Typically these images are made using polarized light, mostly because the resulting pictures are colorful and abstract. But you don't have to make crystals to see objects in a different light.
Take two pieces of polarized film (or two polarized sunglasses), hold them up to a light and turn one while holding the other steady. You'll notice the light darkens at some point. This is because the first polarizing film lets through light that is polarized in a specific plane (imagine the film "flattens" the light into a sheet as it passes through). Turning the other film also "flattens" the light but since the light from the first film is already "flattened" the second film just blocks out light as you rotate it away from the plane of the first film. A photograph of this would be a dark or black image.
But put something between the films that also changes the plane of the light and now the second film doesn't block out all the light - it let's through that light that has been "flattened" by the object between the films, "flattened" to a plane different from the second film. And because the object changes the plane of the light differently depending on the shape and composition of the object, you get color. Here's what that looks like:
This is just a clear plastic disk that sits on top of a stack of blank CD's. To the "naked" eye it's just a clear piece of thin plastic. Put it between polarizing film, though, and it reveals colors from different areas where the plastic changes the polarized light coming through the first film. The colors represent areas of stress the plastic underwent when formed into this shape. A material that exhibits this property is called birefringent. Lots of things behave this way, we just don't see them this way because the sun and light bulbs and candles don't emit polarized light. It's sort of like being told bees see flowers different from us - it's right there in front of you but you aren't equipped to see it.
This is fairly easy to do if you have a polarizing filter on your camera lens and a pair of polarizing sunglasses. Check out various pieces of plastic and see what you've been missing!
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