Several types of lens filters are useful in digital photography.
Lens filters are among the most valuable accessories for digital single lens reflex cameras. The filters improve photographs in ways photo editing software cannot. Sometimes using filters allows a photographer to get a shot he would otherwise not be able to get. Screw-in filters screw onto the front of a camera lens. There are also square filters that slide into a plastic mount.
Polarizing Filters
Polarizing filters remove unwanted glare from non-metallic objects. Polarizers can eliminate glare from foliage, wet rocks, mountain streams and other shiny objects. Polarizing filters also darken blue skies and enhance contrast and color in clouds, according to "The Ultimate Guide to Digital Nature Photography." Polarizing filters come in two types: circular and linear. The type does not refer to the shape of the filter but to how the device polarizes light. Linear polarizers are not recommended for digital cameras because their metering and autofocus sensors do not work properly. Polarizing filters work best when the lens is 90 degrees from the source of light. If the sun is at the photographer's back, the polarizer has minimal affect. If the sun is at the photographer's side, a polarizer will darken the sky and remove unwanted glare.
UV Fliters
UV filters are also called haze or sky-light filters. The filters are clear glass and some photographers use them to protect the front element of the lens from scratches and dirt. UV filters absorb ultraviolet rays and do not affect visible light.
In most situations, people cannot tell when a UV filter is used and when one is not.
Neutral Density Filters
Neutral density filters block the amount of light allowed through the lens. That allows a photographer to use a slower shutter speed to produce motion blur or a larger aperture to give a picture a smaller depth of field. Neutral density filters are gray and look like darkened glass. They come in different strengths. The strengths indicate how many "stops" of light are blocked. If conditions call for a shutter speed of 1/60th of a second, using a 2-stop neutral density filter would allow the photographer to use a shutter speed of 1/15th of a second instead. That would help a photographer make the water In a waterfall or mountain stream look silky.
Graduated Neutral Density Filters
Graduated neutral density filters are a type of neutral density filter. Instead of being dark throughout, graduated neutral density filters gradually go from dark to clear. They are used when scenes have too much contrast for the camera to record it correctly. They are helpful when photographing sunsets. If a photographer meters the brightness of the sky, the foreground would be too dark and create silhouettes. If the photographer meters for the foreground, the sky will be overexposed. Cover the sky with the dark part of the filter and place the clear portion over the foreground. The camera is then able to record detail in both the sky and the foreground.
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