Lens Filters
A lens filter is a small glass or plastic device that screws on to the end of different SLR camera lenses (http://www.thelensflare.com/docs/index.php/Camera_Lenses) to alter color and contrast or to apply a special effect to the scene.
The most popular filters will be discussed in this article.
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Polarizing Filter
This is one of the most common filters for outdoor photography such as nature and wildlife. Its main purpose is to reduce or eliminate reflected glare from non-metallic objects. This causes things like trees, leaves, grass, and water to become more saturated because it removes their highlights. It can also darken the sky, especially when it is used at a right angle to the sun. Make sure that the filter is compatible with the light meter on the camera. Some cameras need a circular polarizer for the light meter to continue to work.
Ultra-Violet Filter
This filter reduces UV light from reaching the camera. This can help improve the detail of an image, and can help slightly darken the sky. It doesn't reduce the overall light in the scene so it's useful to use when a polarizing filter makes the scene to dark. It's also a really good lens protector. It's a lot easier to stomach replacing a $20 filter than it is to replace a $500 telephoto lens.
Neutral Density Filter
ND filters are used to reduce the amount of light hitting the camera. This is useful when the amount of light in the scene is too great for the desired shutter speed. One of the most common uses of an ND filter is to take slow motion water photos. By using a combination of an ND filter, a tripod, and a remote shutter release, a much slower shutter speed can be used and still maintain a good exposure. This causes the natural movement of water to blur, while the static elements of the photo remain sharp.
Graduated Neutral Density Filter
Half of the filter is gray and the other half is clear with a smooth transition between the two. Often landscapes consist of a bright sky and a dark land, and this filter allows the photographer to darken the sky so that the overall exposure of the image is consistent. This effect can be achieved through digital software, provided that the sky isn't completely washed out, but it's less time consuming if the shot is well exposed in the first place.
Warming Filter
These are often amber in color and helps warm a scene by enhancing reds, oranges, and yellows while minimizing blues and greens. This effect can be applied after the fact with digital software by adding a partially transparent amber layer over the top of the rest of the photo; however, the original image will probably need its saturation altered as well to get the desired effect.
Yellow Filter
This increases the contrast in black and white images; however, the same thing can easily be done with digital photo software by adjusting, curves, heuristic levels, or the overall contrast.
Special Effects Filters
There are a variety of special effects filters available. Some will make lights look like stars, some will act as a magnifying lens, and others will distort things to simulate a fisheye. Most of these have a very limited use, and while they may be fun to have, they probably won't be used very much.
Which filters should I buy?
This depends on your individual taste and preferences as well as your subject matter. A UV filter is a must for just about anybody that isn't using a polarizing filter. If nothing else, it will help protect your lens from scratches. An ND filter is great for waterfalls, rivers, and streams and may be of use when the sun is directly in the shot. A graduated ND filter is a must for landscape photographers, and the colored filters are good for specialized instances where altering the color is important for the overall mood of the shot. It's often quicker to use a filter than it is to alter the photo's color during post production; however, with software you're not limited by the exact color of the filter.
About the Author
Brian Broderick (http://www.brianbroderick.com) is a semi-pro nature photographer and the creator of The Lens Flare. His hobbies include hiking, skiing, and computer graphics, and is currently a web programmer.
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