Designed so that absolutely no color from the entire visible spectrum prevails, the neutral density filters can be used in many different contexts, depending on which type is used : uniform shading (square) or graduated shading (rectangular).
Uniform ND filters reduce the quantity of light that reaches the sensor – or the film – increasing the exposure time. These filters have 3 main practical applications:
- emphasizing the flow of movement,
- reducing the depth of field,
- avoiding overexposure.
Graduated ND filters are used to reduce the contrast difference of a composition. They allow for a well-balanced image; they are the filters most used by landscape photographers to yield both harmonious skies and detailed foregrounds at once.
With these filters, images which are impossible to obtain in digital post-processing can be created. The neutral density filters are also currently used in filmmaking and video to maintain a constant shutter speed for example.