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Tuesday, February 14, 2012

Do More With Your Polarizer


It’s the ultimate outdoor photography landscape filter, and we’ll show you how to do more than just darken skies

This Article Features Photo Zoom
4 The polarizer as impromptu neutral-density filter. A polarizer also can be used as a two-stop neutral-density filter by dialing it to maximum polarization (minimum light). In the image of a redbud above the surging Merced River, even at ISO 100 and ƒ/32, I couldn't reach the 3⁄4 sec. shutter speed that would give me the motion blur I wanted. But the two stops of light I lost to my polarizer were just enough to get me where I wanted to be.

5 Is this a good scene for a polarizer? When you approach a scene, ask yourself, does this scene call for a polarizer? Get used to trying your polarizer for everything you possibly can. To determine the polarizer's effect, rotate the outer element 360 degrees as you peer through your viewfinder or while viewing the LCD in live-view. Often, just holding the polarizer to your eye and rotating it slowly is enough to determine its benefit. Either way, if you can't see a change, you probably don't need to worry about a polarizer.

Because a polarizer also can enhance reflections and glare, whenever the polarizer is on, I strongly urge you to test its effect with every composition and especially after switching from horizontal to vertical orientation. Unless I'm trying to maximize a reflection, I rotate the polarizer until the scene appears darkest. If there's no apparent change, I watch specific objects that might have a slight sheen like water, a leaf or a wet rock as I rotate the polarizer. I almost always find some change.

Three Polarizer Pitfalls To Avoid
> Lost light. A polarizer costs you one to two stops of exposure, depending on the polarizer and the amount of polarization you dial in. Since aperture manages depth, landscape photographers usually compensate for the lost light with a longer shutter speed—one more reason to use a tripod.

> Differential polarization. Because a polarizer's effect varies with the direction of the light and wide lenses cover such a broad field of view, light strikes different parts of a wide scene from different angles. The result is differential polarization: parts of the scene that are more polarized than others.

Differential polarization is particularly troublesome in the sky, appearing as an unnatural transition from light to dark blue across a single frame. This effect often can be reduced, but rarely eliminated, with careful dodging and burning in Photoshop. Better yet, avoid images with lots of boring blue sky.

What, Exactly, Does A Polarizer Do?

It helps some people to understand that a wave of light oscillates perpendicular to its direction of motion—picture the way a wave in the middle of the ocean rises and falls as it advances. The wave moves forward, but the water moves up and down. In simple terms, by removing light that oscillates in a specific direction, a polarizing filter removes reflection. Polarization (reflection reduction) is most pronounced when your lens points 90 degrees (perpendicular) to the direction of the sun (or other light source); it's least effective when the lens points directly toward or away from the sun.

A circular polarizer, which is what you want for today's DSLRs, screws to the front of your lens. Rotating the polarizer's outer element relative to its fixed, inner element varies the orientation and amount of polarization. You can see its effect through your viewfinder or on your live-view LCD.


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