Tuesday, April 24, 2012
Gadget Bag: Anatomy Of The Polarizer
What makes one polarizer different from another?
Filters are coated with microscopically thin layers of chemicals that enhance light transmission by reducing reflection. The coating that faces the lens surface blocks internal reflections. Held at an angle, a UV or 1A filter reveals its antireflection coating by glistening a greenish or purple sheen, but you may not see such evidence on a polarizer. Another sort of coating—let's call it the environmental coating—protects filter surfaces from fingerprints and cleans easily without scratching.
The polarizing filter may not be the most important filter you can buy, but without doubt, it's the one that all photographers should own. Polarizers are sold with a single purpose—to reduce or eliminate surface reflections and thereby improve color rendition. Of course, that means they allow us to see beneath the surface of water. A fortunate by-product is that they also darken a blue sky without shifting its color. Another benefit that's often overlooked is that a polarizer can be a last-ditch neutral-density filter, usually absorbing two stops of light.
You also can buy polarizers that slightly warm the scene and some that create dramatic color shifts that change as you rotate the filter.
These warming polarizers usually offer a range of hues between two complementary colors, for example, blue/yellow or red/green, made possible because of a property called birefringence. With some models, you can adjust the intensity of one single color.
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