Neutral Density Filters Explained

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What is a Neutral Density Filter, and what do you use it for?

A neutral density filter or ND filter  –  The purpose of a standard photographic neutral density filter is to reduce light entering the lens. Doing so allows the photographer to select combinations of aperture, exposure time, and sensor sensitivity, otherwise producing overexposed pictures. This is done to achieve effects such as a shallower depth of field and motion blur of a subject in a broader range of situations and atmospheric conditions.

Neutral density filters are often used to achieve motion blur effects with slow shutter speeds.

Examples of this use include:

  • Blurring water motion such as streams and waterfalls.
  • Reducing the depth of field.
  • Add motion blur.
  • Extend the length of the exposure.

You can photograph a waterfall at a slow shutter speed to create the milky water effect. You might determine that a shutter speed of five seconds will be needed. On a very bright day, there might be so much light that even at a minimum aperture, the five-second shutter speed would let in too much light and the photo would be overexposed. In this situation, you are applying an appropriate neutral density, allowing less light to come into the camera and enabling you to have a longer shutter speed.