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Thursday, November 1, 2007

Using Graduated Neutral-Density Filters


From polarizers to graduated NDs, filters are part of every outdoor photographer‚’s life. Try these techniques to help you enhance or correct your images in the camera.


Using Graduated Neutral-Density FiltersThe sky over this field of California poppies is a little light in a straight shot (above); adding a polarizing filter makes the sky look better (below).

4 Use a polarizer to‚ "see" through water. Interesting things can lie just beneath the surface of lakes and streams. Polarizers can cut the glare from the surface of water and allow us to see colorful rocks and interesting patterns. These make great foregrounds for landscapes, as well as interesting subjects on their own.

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Save the streams. While polarizers are effective in removing glare from water surfaces, sometimes they’re too effective, essentially making streams disappear. If you have a stream in your photo, the viewer needs to know it’s there. I like to turn the polarizer to its maximum effect and then back it off just a bit, restoring a little glare on the surface of the stream. Otherwise, the stream can look more like a trail or a road rather than a stream.

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Use a polarizer instead of a graduated ND filter to darken the sky. If you have a blue sky that’s just a bit too light, say about a stop too light, which often happens near the horizon, you can probably darken it with a polarizer rather than using a one-stop graduated ND filter. This way, you get the sky the way you want it, along with the added benefit of cutting glare from foliage.

Using Graduated Neutral-Density Filters Rain on the polarizing filter turns this into an ethereal imag

The polarizer will have a greater effect if your camera is pointed 90 degrees to the sun, in other words, when the sun is either to your left or right. Be careful when using a wide-angle lens, though. Because a wide-angle lens takes in a large angle of view across the sky, it’s very easy to have one part of the sky appear darker than the rest.

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Use a polarizer to dial in the sky. As we’ve just seen, it’s possible to darken skies using a polarizer. But sometimes it’s easy to go overboard, and the result can be a nearly black sky. This most often happens at higher altitudes.

Many people turn the polarizer to its maximum effect because that’s what looks best in the viewfinder—that’s what gives us that "oooh" effect. But remember, film and digital sensors don’t see things quite the same way we do. Compared to our eyes, film and sensors are capable of recording only a very narrow range of brightness values. Therefore, that deep blue sky you see in the viewfinder may look nearly black to your film or digital camera. The way to know how the sky will be rendered ahead of time is to use your in-camera spot meter in the manual exposure mode.

Using Graduated Neutral-Density Filters

Lee Polarizer

Here’s how: Look through the view-finder and rotate the polarizer until you like what you see. Determine an exposure in the manual exposure mode by spot-metering something in the scene (not the sky) that has a medium tonality (the same reflectance as a gray card). Change your aperture and shutter as you normally would to set an exposure and zero-out the meter.

Now, point your spot meter to the sky and watch the analog meter in your viewfinder. Normally, skies look best if they’re a little lighter than a gray card. If your meter reads darker than medium (on the minus side of the scale), the sky will look unnaturally dark. If it reads -2, the sky will be nearly black. This can be dramatic, but is it what you want? If not, turn the polarizer until the sky is a little lighter and repeat the above metering exercise. Do this until the meter indicates that the sky is the tonality you wish it to be. You may find that you didn’t need the polarizer in the first place.

Using Graduated Neutral-Density Filters B+W Polarizer

For example, in the first picture of the red rocks, they’re of a medium tonality. The light-colored sandstone in the foreground is about one stop lighter than medium. But the sky is about two stops darker than medium. This is what can happen from overpolarizing. By using the spot meter, I can tell ahead of time if this will happen and take steps to correct it, as shown in the second picture.

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Do I need a polarizer? If you’re not sure you need to use a polarizer, instead of taking the time to attach it to your lens, simply hold one to your eye and rotate it. If you see something you like, go ahead and attach the filter to your lens. Some polarizing effects are subtle, like when you want to reduce glare from leaves. In this case, keep your eye on a small section of the scene rather than the whole. Be sure the filter threads are facing you, just as they would be on the lens.


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