Neutral density or ND filters have the sole purpose of cutting down the amount of light as a whole. A perfect neutral density filter would transmit all wavelengths of light equally, so there would be no color change. Though not actually perfect, it can be used equally well in both color photography or black and white photography.
It is made in a wide variety of densities. Depending on the manufacturer, there are currently two rating systems commonly used to designate the density of neutral density filters.
- A straightforward system of whole numbers whereby an ND-1 indicates a need for a 1-stop exposure increase; ND-2 is two stops; ND-3 is three stops; and so on.
- In the other, which is scientifically oriented, the decimal number .3 indicates a 1-stop exposure increase need; .6 is for two stops; .9 is for three stops; and so on.
Typical Uses of ND Filters:
1. To Blur Action – Sometimes it is desirable to use a relatively slow shutter speed to indicate movement or to show an object’s path. If a fast film is in use in bright light, or if a wide aperture is needed to limit depth of field, the correct exposure might ordinarily require an undesirably high shutter speed. An appropriate neutral density filter makes any desired shutter speed possible.
2. To Reduce the Effect of Transitory Events – Long exposures can “remove” all moving objects from a picture. That is, if you are photographing a building or site under circumstances where passing automobiles, pedestrians, or site workmen might be unwanted picture elements, the use of a long exposure will delete such transitory presences; they will not be in one place long enough to record on the film. (In long time exposures an allowance must be made for reciprocity failure.
3. To Reduce Depth of Field – By keeping the shutter speed unaltered when neutral density filters are introduced, the lens aperture can be opened to reduce the depth of field in the image. The use of shallow depth of field, remember, tends to visually isolate the subject, because everything not in the principal plane of focus will appear not sharp.
4. To Prevent Overexposure of Fast Film – In very bright light, you may find it impossible to avoid overexposing a very fast film, especially with the very large and relatively slow shutters found on view camera lenses. (These frequently limit fast speeds to no more than 1/125 or 1/250 of a second.) Occasionally, you might find yourself with only one type of film remaining unused at the end of a day and then be faced with a situation that requires slower films. By reducing the amount of light entering the camera, neutral density filters allow greater exposure flexibility.
5. Exposure Effects – Several applications of neutral density filters make use of their light-absorption qualities.
About the Author:
Clance Lee (basiccameraphotography.com) is a freelance photographer, mostly taking wedding photographs and portraits. Other than photography, he likes to travel around and occasionally does travel reviews.
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