Definition: Neutral Density Filters

Definition: Neutral Density Filters | Glossary entry

Neutral Density Filters

Neutral Density (ND) Filters are placed in front of the camera lens to reduce the light intensity entering the lens. The use of an ND filter does not affect the colour or hue of the light that passes through it. ND filters affect all visible light equally. As a result there are no colour casts.

An ND filter is used in a number of ways…

  • The reduction in the intensity of incoming light allows you to open the aperture wider or to keep the shutter open longer, or a combination of both.
  • A low level of filter, say an ND 4 filter (cuts 4 stops of light) can simply help cope better with very bright conditions.
  • Enables longer shutter opening. This allows you to add creativity into your shots. Here are some creative uses for ND’s…
    • Blurring the motion of water (e.g. waterfalls and rapids).
    • Shallow Depth of Field in bright light (wide aperture would normally over-expose).
    • Make fast moving objects invisible.
    • Add motion blur to moving things in your shot.
    • Extend your exposures to capture more detail.
    • Increasing contrast/lowering brightness – great for moon shots

You can carry out any photographic operation with an ND filter attached to your camera. As it reduces the incoming light you can avoid reducing the aperture to reduce light. This allows you greater flexibility to set the shutter speed appropriately for the motion blur.

When using ND filters you will have to work in manual mode. The camera light meter will be miss-leading behind the filter and because the light conditions will be variable. It is advisable to try out a few shots to get the shutter timing right.

There are a range of ND filters of different densities…
ND 2 (reduces incoming light by two stops);
ND 4 (reduces light by four stops);
ND 8 (reduction 8 stops);
ND 10 (10 stop reduction).
Other densities exist but they are not very common.

Graduated neutral density filters

There is also a ND filter called an ND grad, or Graduated ND filter. These are special ND filters where half the filter is ND grey and the other half of the filter is clear. This allows an arrangement of the filter so it reduces the light through half the filter. Used in the correct way, the light can be reduced from, say, the sky. At the same time the clear part of the filter allows the normal light through from the darker areas below the sky. This balances the exposure and allows the sky to exposed without blowing out to pure white.

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