page_title: Neutral-density filter
section_title: Uses
hierarchical_section_title: Neutral-density filter / Uses
caption_attribution_description: Deutsch: Gegenüberstellung eines Bildes nur mit Pol-Filter und einem Bild mit Pol- und 1000x ND-Filter (ND3.0). 1000x ist die Filterbezeichnung, der eigentliche Filterfaktor beträgt aber ca. 1666! Zu sehen ist Pritzerbe. Im Vordergrund: Schwemmwiesen der Havel. English: Comparison of two pictures showing the flooded meadows in Havelsee to show the result of using a ND-filter. The first one was taken using only a polarizer and the second one was taken using a pol and a 1000x ND-Filter (ND3.0), which allowed the second shot to have a much longer exposure, smoothing any motion. Although the filter labels 1000x, the real filter factor is ~1666! Français&#160;: Comparaison de deux images démontrant l'intérêt d'un filtre ND sur un paysage. La première a été prise avec un polariseur uniquement et la seconde avec un filtre ND 1000x (ND 3.0), ce qui lui permet une exposition et un lissage plus grands.
context_page_description: In photography and optics, a neutral-density filter, or ND filter, is a filter that reduces or modifies the intensity of all wavelengths, or colors, of light equally, giving no changes in hue of color rendition. It can be a colorless or grey filter, and is denoted by Wratten number 96. The purpose of a standard photographic neutral-density filter is to reduce the amount of light entering the lens. Doing so allows the photographer to select combinations of aperture, exposure time and sensor sensitivity that would otherwise produce overexposed pictures. This is done to achieve effects such as a shallower depth of field or motion blur of a subject in a wider range of situations and atmospheric conditions.
  For example, one might wish to photograph a waterfall at a slow shutter speed to create a deliberate motion-blur effect. The photographer might determine that to obtain the desired effect, a shutter speed of ten seconds was needed. On a very bright day, there might be so much light that even at minimal film speed and a minimal aperture, the ten-second shutter speed would let in too much light, and the photo would be overexposed.
context_section_description: The use of an ND filter allows the photographer to use a larger aperture that is at or below the diffraction limit, which varies depending on the size of the sensory medium (film or digital) and for many cameras is between f/8 and f/11, with smaller sensory medium sizes needing larger-sized apertures, and larger ones able to use smaller apertures. ND filters can also be used to reduce the depth of field of an image (by allowing the use of a larger aperture) where otherwise not possible due to a maximal shutter speed limit.
  Instead of reducing the aperture to limit light, the photographer can add a ND filter to limit light, and can then set the shutter speed according to the particular motion desired (blur of water movement, for example) and the aperture set as needed (small aperture for maximal sharpness or large aperture for narrow depth of field (subject in focus and background out of focus)). Using a digital camera, the photographer can see the image right away and choose the best ND filter to use for the scene being captured by first knowing the best aperture to use for maximal sharpness desired. The shutter speed would be selected by finding the desired blur from subject movement. The camera would be set up for these in manual mode, and then the overall exposure adjusted darker by adjusting either aperture or shutter speed, noting the number of stops needed to bring the exposure to that which is desired. That offset would then be the amount of stops needed in the ND filter to use for that scene.
  Examples of this use include:
  Blurring water motion (e.g. waterfalls, rivers, oceans).
  Reducing depth of field in very bright light (e.g. daylight).
  When using a flash on a camera with a focal-plane shutter, exposure time is limited to the maximal speed (often 1/250th of a second, at best), at which the entire film or sensor is exposed to light at one instant.  Without an ND filter, this can result in the need to use f/8 or higher.
  Using a wider aperture to stay below the diffraction limit.
  Reduce the visibility of moving objects.
  Add motion blur to subjects.
  Extended time exposures.
  Neutral-density filters are used to control exposure with photographic catadioptric lenses, since the use of a traditional iris diaphragm increases the ratio of the central obstruction found in those systems, leading to poor performance.
  ND filters find applications in several high-precision laser experiments because the power of a laser cannot be adjusted without changing other properties of the laser light (e.g. collimation of the beam). Moreover, most lasers have a minimal power setting at which they can be operated. To achieve the desired light attenuation, one or more neutral-density filters can be placed in the path of the beam.
  Large telescopes can cause the Moon and planets to become too bright and lose contrast. A neutral-density filter can increase the contrast and cut down the brightness, making the Moon easier to view.
caption: Comparison of two pictures showing the result of using an ND filter at a landscape. The first one uses only a polarizer, and the second one a polarizer and a 1000× ND filter (ND3.0), which allowed the second shot to have a much longer exposure, smoothing any motion.
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