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.
5 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.
6 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.
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.
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.
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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