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Tuesday, April 24, 2012

Gadget Bag: Anatomy Of The Polarizer

What makes one polarizer different from another?

Labels: Gadget BagGear
This Article Features Photo Zoom

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.

B+W is widely known for filter innovation and for producing high-quality filters. They were the first to offer multilayer coating that repels water and dirt. The coating is harder than glass and protects the filter from scratches. The Kaesemann Circular Polarizing Multi-Resistant Coating (MRC) filter, available in all popular sizes, is constructed from select polarizer foils and specially formulated optical glass. Kaesemann ("encased") filters are sealed at the edges for maximum durability under extreme climatic conditions.

Cokin Varicolor filters are available in several color combos, including pink/orange, blue/lime and red/blue. In addition, Cokin offers red, blue and yellow Polacolor filters that shift from normal polarization effect to polarizer-plus-color as you twist. Cokin polarizers offer the money-saving advantage of being able to move from a lens of one diameter to a lens of a different diameter because they attach via an adapter. Cokin filters can be used with many compact digital cameras, too.

The Formatt Circular Schott-Desag B270 Crown Optical Glass Polarizer is constructed using crystal-clear white-water optical glass. The absolute clarity of the glass, combined with advanced polarizing material, makes these polarizing filters especially potent and free of color shift. Each and every filter delivers guaranteed flatness to a maximum two-wave value and comes with an individual reading from a laser interferometer. Formatt has been making filters using the finest high-quality materials and most advanced technology for three generations.


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