Gadget Bag: Anatomy Of The Polarizer

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Why do some 52mm polarizing filters cost nearly $200 and others less than $20? Maybe a better question is: Why do some photographers spend $200 for a polarizer when there are alternatives available for a fraction of that price?

Across the various brands, different models offer specific characteristics, which you may or may not need, depending on the type of photography you do. Although many brands and models look the same at first glance, there are at least 10 major ways in which they may differ—and those differences can have a powerful effect on the captured image. Once you understand the variations, you can decide what works best for you and your photography.

The great majority of polarizers in use today are circular polarizers. Most autofocus cameras and cameras that use a beamsplitter or semi-silvered mirror require a circular polarizer.

If you're not using autofocus, a less expensive linear polarizer will work for you, but for the vast majority of shooters today, the circular polarizer is best. While they're not interchangeable, both do the same thing, and both are available in plastic and glass versions.

As optical materials go, plastic has a bad connotation, but it does offer lighter weight, and that can be a plus. Glass is generally regarded as superior, not only because of intrinsic properties, but because sheets of glass can be more readily made plano-parallel. That means that the front and rear surfaces are exactly the same distance apart, no matter where they're measured. In other words, plano-parallel filters are perfectly flat on both sides, and the two surfaces are parallel at all points.

Of course, not all glass is created equal. Some high-quality filters are made from glass that's specially formulated to provide certain performance characteristics. In the same way that glass elements in camera lenses have differing refractive indices, the optical properties of glass used to make filters can vary widely. It's important to remember that when you place a filter in front of a lens, it becomes part of the optical formula for that lens. No light reaches the sensor or film without passing through it. Quality is of paramount importance.

Filter dimensions matter, and not just the diameter. Filter thickness influences performance in several ways. A polarizer that's too thick overall and that sits too high in the filter ring can cause vignetting, especially with wide-angle lenses and kit zooms. Filter thickness can sometimes affect density, as well. Increased density means less light passes through—and that means increased exposure time. Not all polarizing filters have the same exposure-compensation factor.

Manufacturers typically make the exposure-compensation factors available so it's easy to compare the specs of one versus another.

The composition of the threaded ring is also important. It can be made of steel, brass, plastic or other materials. Dissimilar metals tend not to get stuck when screwed together, so brass is the material of choice for attachment to the steel threads found on lens barrels. Also, brass is a very stable metal that doesn't readily contract or expand like an alloy. Because polarizers are rotated during use, extra stress is placed on the threads. It's easy to overtighten a polarizer, so many high-quality filters are made with brass bodies.

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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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Heliopan filters are available in every imaginable size and configuration, including 13 different types of polarizers and special-effects filters. They're made from glass supplied by Schott, which is wholly owned by Carl Zeiss and set in black anodized brass rings that screw in with precision. Heliopan thin circular polarizers accommodate ultrawide-angle lenses. The High-Transmission Circular Polarizing Multi-Coated Filter features SH-PMC multilayer coating, which transmits 98.8% of light and absorbs only one ƒ-stop, thereby enabling exposure flexibility.

Hoya is one of the world's largest manufacturers of optical glass, including glass used for camera lenses, eyeglasses and photographic filters. Their production process involves the introduction of raw elements and chemicals to molten optical glass to produce a filter of uniform coloration. The Pro 1D filters are designed exclusively for digital cameras and offer advanced features like enhanced multicoating, black-rimmed glass and low-profile frames that don't cause vignetting on wide-angle lenses. They're available in sizes up to 82mm.

Kenko Zeta Wideband Circular Polarizers are handsome and precise, and are supplied in the most unique protective cases imaginable. They're constructed using premium quality polarizing film and are treated with ZR (Zero Reflection) Super Multi-Coating. They sport an ultrasmooth surface that's stain- and scratch-resistant thanks to Kenko's proprietary Nano Glass Technology. The ultrathin threaded ring is compatible with wide-angle lenses. Kenko Zeta polarizers can be found in sizes from 49mm through 82mm.

Pro-Optic circular polarizers are well made and very affordable. Although their price tag says "budget," their quality and performance puts them right up there with the higher-priced brands. A 52mm C-PL, for example, will set you back less than $20. Made in Japan of the highest-quality materials and optical glass, Pro-Optic polarizers are a good choice especially when you need to cover many different sizes. Adorama offers an attractively priced assortment of filter accessories for Pro-Optic (and other) polarizers, including screw-in metal lens caps, metal lens shades and stack caps.

Singh-Ray calls their polarizers "Lighter, brighter" because they transmit more light than average and require less exposure compensation. The LB ColorCombo Warm Circular Polarizer/LB Color Intensifying Filter provides full polarizer benefits, plus color enhancement for outdoor scenes, particularly reds, browns and greens. The thinner-mount version of this filter can be used on lenses as wide as 12-24mm without corner vignetting. They also can be used in conjunction with the Galen Rowell Graduated Neutral Density Filters.

The Tiffen Company has earned Oscars®, Emmys® and numerous other awards. The Digital High Transmission (DHT) Circular Polarizing Multi-Coated Filter is constructed of high-quality optical glass and available in all popular sizes. Tiffen's patented ColorCore technology assures that the filter is given the highest scratch-resistant durability available.