Neutral Density (ND) Filters

Neutral density filters are essentially gray filters designed to equally reduce the amount of light hitting the camera’s sensor, thereby increasing exposure times. Neutral density (ND) filters are most useful when a long exposure time is desired but not attainable given the available lighting.

ND filters have two main purposes:

  • Create a wider aperture. With a fixed shutter speed, a wider aperture can be used which will yield the same exposure. A shallower depth of field can be achieved even if the photographer is limited by the maximum shutter speed of the camera. The ND filter will allow for the photographer to keep the fixed shutter speed and still reach bigger apertures.
  • Create a slower shutter speed. With a fixed aperture, a slower shutter speed (longer exposure time) is achieved. A slow shutter speed can be obtained on sunny or slight overcast days when it would otherwise be impossible. The ND filter can lessen the amount of light hitting the camera and allow the photographer to choose a slower speed to show motion effects.

Neutral density filters have gradings associated with the amount of light they reduce. The higher the grading, the more light is reduced, and the wider the aperture or slower the shutter speed can be set. ND filters are commonly rated by the density of the filter. For each filter density of 0.3, the camera’s f-stop is reduced by 1, and the darker the filter will appear. The below chart explains a wide array of ND filters, the associated density, and the amount of f-stop reduction.

Filter Optical Density

f-stop Reduction

ND2

0.3

1

ND4

0.6

2

ND8

0.9

3

ND64

1.8

6

ND1000

3.0

10

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