Fix Common Photo Problems With a Polarizer

Tag: Linear Adapter

We've become so spoiled by the magic of digital photography that we tend to assume that it's possible to do pretty much anything digitally. Improve exposure settings after the photo was taken? Check. Sharpen a photo? Natch. Move your subject from one photo to a completely different one? Piece of cake. But there's one effect that you really can't replicate digitally: the effect of a polarizer.

A polarizer, also called a polarizing filter, sounds like something that only a physicist could love. When light hits an object, it tends to bounce and reflect in a somewhat haphazard manner, causing the light waves to modulate in all directions. A polarizer allows the light that's modulated only on a single axis to pass through the camera lens, and it blocks light modulated along all other axes.

That's the Mister Science explanation. Here's a more practical one: Unpolarized light is the nemesis of great photos. It causes reflections in glass and water, and also contributes to low contrast, hazy-looking skies. When you use a polarizer, you can virtually eliminate reflections and add snap to the skies in your photos in a way that's simply impossible to achieve using a photo editing program.

Intrigued? To join the fun, you'll need to get a polarizer. Most polarizing filters screw onto the front of your camera lens, so you need to find the diameter of your lens (usually marked on the side of the lens, and measured in millimeters). You can go toPCW Shop & Compareto browse some options.

If your camera lens doesn't have screw threads, you might be able to snap a filter adapter onto the front; check your camera's user guide for details.

There are two different kinds of polarizers to choose from: linear and circular. Don't bother with linear polarizers; they mess with your camera's exposure meter, meaning that your camera will set the wrong automatic exposure. Circular polarizers don't have that problem.

If you already have a filter on the front of your camera lens (such as a skylight, UV, or haze filter), remove it. Stacking filters is not a good idea, because it can cause vignetting. In other words, the filter might stick out so far that it intrudes into the photo, causing a dark blurry obstruction around the edge of the picture.

A polarizer is not the sort of filter you'll want to leave on your camera all the time: It dramatically reduces the amount of light reaching your sensor, so it's not a good idea to use it indoors or in low light. But it can come in handy as a "neutral density" filter, letting you get more even exposure in extremely bright scenes or shoot at a slower shutter speed to capture motion blur at midday.

So much for the basics; now it's time to take some photos. A polarizer has two parts: a base that screws into the camera lens, and a rotating collar that you can spin with your fingers as you prepare to take the picture. Keep an eye on the scene in the viewfinder as you turn the filter, and you'll find that the effect changes. At the point of minimal polarization, the scene will look the same as when there's no filter on the camera. Spin the filter 90 degrees from there, though, and you'll see the effect increase. Continue to spin the filter, and the effect will diminish. Just rotate the filter until you see the effect you like best and take the picture.

It's worth noting that you'll get the best effect when shooting 90 degrees (perpendicular) to the sun. Shooting straight towards or away from the sun will generally cause the filter to have no effect on the scene, no matter how much you rotate the polarizer.

And as I mentioned earlier, the polarizer's effect varies. In its minimal position, you get the same results as if the polarizer were not attached at all. In this photo, you can see the pale sky, with patches of anemic blue.

Before I took this photo, I rotated the polarizer about 90 degrees. Most of the photo appears unchanged, but the sky now pops--there's a lot more contrast between the sky and clouds, and the blue is deeper and more dramatic.