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What 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 (oscillates). In very 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); its least effective when the lens points directly toward or away from the sun.
A circular polarizer (what you want for today’s digital SLR cameras) screws to the front of your lens; its polarized glass element rotates on its fixed frame. Rotating the polarizer’s element relative to the fixed lens, varies the orientation and amount of polarization. You can see its effect (sometimes large, sometimes small) through your viewfinder or on your live-view LCD.
What a polarizer does for you
With reflections minimized by a polarizer, pale blue sky is transformed to a deep blue, glare is removed from rocks and foliage to reveal natural color and texture, reflections are removed from water to reveal color and submerged features, and clouds that were barely visible suddenly snap into prominence. Or imagine mountains reflected in a still alpine lake: As you rotate your polarize, the reflection is replaced by rocks and leaves dotting the lakebed; keep turning and the reflection returns.
Polarizer Applications
Polarizer on a budget
All scenes don’t benefit equally from a polarizer, and photographers on a budget can’t always afford one for every lens. If you’re only going to go with one polarizer, buy one for your largest lens—as long as you’re on a tripod, it’s quite easy to hold a larger polarizer in front of a smaller lens as you shoot.
Does this scene call for a polarizer
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 can also enhance reflections (and glare), whenever the polarizer is on, you must, must, must 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 (water, a leaf, or a rock) as I rotate the polarizer—I almost always can find some change.
It’s not just for the sky
As nice as the the effect on the sky is, it’s the polarizer’s more subtle ability to reduce glare in overcast or shade that I find irreplaceable. Peering through your viewfinder (or watching your LCD if you’re using live-view), lock your eyes on a reflective surface and rotate the polarizer. The effect is most obvious on water, or wet rocks and leaves, but even when completely dry, most rocks and leaves have a discernible sheen. As you rotate the polarizer, harsh glare is replaced by natural color and texture; continue rotating and the glare reappears. The glare is minimized when the scene is darkest.
Regardless of the effect, there’s no rule that requires you to turn the polarizer to one extreme or anther (maximum or minimum reflection). Rotate the outer element slowly and watch the scene change, stopping when you achieve the desired effect.
In the North Lake autumn reflection scene at the top of the page, I was able to find a midpoint in the polarization that kept the best part of the reflection (the mountains and trees), while still revealing the submerged granite rocks at my feet.
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