Neutral density filters reduce the amount of light that enters a lens.
A neutral density filter is a colorless or gray filter that fist on a camera lens. It reduces and modifies the wavelengths of color that enter the camera lens without changing the hue. A neutral density filter gives the photographer more flexibility with exposure settings and allows her to accurately expose for scenes with a range of brightness.
Function
A neutral density filter allows the photographer to increase dynamic range---the camera's ability to accurately expose for a scene with very dark and very light elements. The ND filter can be used to maintain a small aperture while slowing down the shutter speed to capture motion, such as blurred water in a river or lake.
Reduced Light
Adding a ND filter to the camera lens will reduce the exposure value because the filter restricts light coming into the lens. Typical filters reduce light at one, two and three stops (units of measure for photography settings).
Slow Shutter Speeds
By adding a ND filter, a small f-stop number can be used in conjunction with a slow shutter speed to blur motion. If more depth-of-field is required, an even slower shutter speed must be used to correctly expose the scene while using a ND filter. Use a tripod when shooting with shutter speeds under 1/25 of a second.
Varieties
There are several types of neutral density filters. The graduated neutral density filter is like a regular ND filter except the filter doesn't have the ND effect on the entire filter, it's graduated from full ND to completely clear. A graduated ND filter is used when one region of an image is brighter than the rest, such as a sunset framed by mountains. Using a graduated ND filter for this scenario allows you to also expose for the mountains while maintain a rich sunset.
Uses
Landscapes photographs benefit from using a ND filter because of increased dynamic range. Neutral density filters add a creative element to photographing water fountains, waterfalls or bodies of water. Creating motion blur in the water gives it a dreamy feel, a look that our eyes cannot see.
Tags: camera lens, density filter, density filters, neutral density, neutral density filter