Monday, December 31, 2007

January/February 2008 HelpLine

helplineQ) I'm trying to figure out how the exposure compensation works on my digital SLR. It doesn't seem to affect the metering. Am I using it the right way, or is there a problem with my camera?

Lindsay Miller Published in HelpLine
January/February 2008 HelpLine

Learning To Polarize

Q) I'm finally getting around to getting a polarizer for my camera. I've read your explanation about circular polarizers in a previous HelpLine, so I know what to get. Now I would like to learn more about using them.

D. Franklin
Via the Internet

A) Polarizing filters can be used in many situations. You can use them to remove some glare and reflections in your scenes, but you can also use them to increase contrast and saturation in skies. It's just a matter of mounting the filter on the lens, rotating the ring and looking in the viewfinder to see which reflections are reduced. But before I talk about specific uses, I have two suggestions to prevent damage to the filter.

First, identify the part of the filter that turns and get comfortable adjusting it. If you look at the edge of a polarizing filter, you'll find that there's a part of the "ring" that freely turns and a part that's stationary. The stationary section is used to screw the filter on the lens, while the free-turning section is used to adjust the effect. Since you'll often adjust the polarizer while looking through the viewfinder, it's important that you turn the right thing. If you continually reach for the stationary part, you could end up screwing the filter on so tight that it's difficult to get it off the lens.

Second, it's a good idea to turn the filter in the same direction as you'd turn it to mount the filter on the lens. (This would be clockwise as viewed from the front of the camera and counterclockwise when your eye is up to the viewfinder.) Getting into this habit helps to keep the filter securely mounted on the lens. If you were to turn the filter in the "loosening" direction, there's a chance that eventually the filter would unscrew and fall off the lens.

Now, on to using a polarizer in your photography. The typical application for polarizers is for outdoor landscape shots with a blue sky and some clouds. With a polarizer, you can increase the saturation of the sky to create a deep blue that will make the clouds pop out. To achieve the greatest effect with the polarizer, shoot at right angles to the sun in order to take advantage of the polarizer's ability to block light that's in a different "phase." Too often I've run across people trying to use a polarizer to deepen skies while shooting into the sun. Then they wonder why the polarizer isn't working.

When shooting skies, you should consider how strong an effect you want. I see images all the time that shout out "polarizer" because the sky is an unnatural blue. Obviously, that's a creative call on your part, but it's a good thing to keep in mind when you're "dialing in" the polarizing effect.

If you shoot panoramas (multiple shots that you stitch together later in the computer), you'll have to forgo the polarizer. Since the effect of the filter is dependent on the angle to the light source, as the camera is rotated, the sky will be affected differently with each shot. This makes it difficult to achieve smooth seams between images when you stitch them together.

A polarizer can be useful for water shots where there are a lot of reflections that diminish your images. Once again, the polarizer is dependent on the angle of reflection. Although it can be hard to predict its effectiveness, that shouldn't make you think twice about trying the polarizer.

If you just want to quickly check how well the polarizer will work in a composition, you don't have to mount it on the camera. Just hold up the filter to your eye and look through it while turning it back and forth to see the effect. Watch out if you're wearing polarized sunglasses because the combination of two polarizing filters can black out the whole image or half of the image. (Actually, polarized sunglasses can be useful for previewing filter effects. Just rotate your head back and forth to see the effect.)

A polarizer isn't just for outdoors. If you're shooting shiny objects with reflections, or even objects that you don't perceive to be shiny, a polarizer can help minimize the glare that reduces detail and contrast in your image.

My final tip about when to use a polarizer has nothing to do with glare or reflections. In a pinch, a polarizer can be used as a neutral-density filter to reduce the amount of light coming into the camera.

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