Definition and function

Gray filters, or neutral density filters (ND filters) called, are used in photography and on film and television cameras. An ND filter is a screw attachment for lenses with mounted glass or plastic discs, which should produce an even darkening of the image. This is made possible by a uniform gray coloration of the filter. On gray filters reduces the amount of light falling on the camera sensor by a defined factor. This extends the shutter speed by a few glare levels.

The strength – with reference to the light attenuation – of a gray filter is given by the so-called extension factor. This ranges from 1 to 100,000,000, with 1 permeating 100% of the light and 100,000,000 only 0.000001%. Commercially available ND filters have extension factors of 2, 4 or 8, the corresponding labeling of the filters in these cases would be „ND 2X“, „ND 4X“ and „ND 8X“. The same applies to all other extension factors.

applications

A reduction in the amount of incident light can be useful in many ways. Often come gray filters used when the technical possibilities of the camera or the lens do not allow light reduction. This is the case when the photosensitivity of the camera is too high or the lens can not prevent overexposure by its Abblendmöglichkeiten. Mostly, however gray filters Used to create a motion blur under the same lighting conditions and thus capture the dynamics of a subject. The most well-known examples of such flow and wipe effects are photographs of waterfalls that act as a uniformly soft curtain. Such flow effects due to long exposure times are also often used in architectural photography to eliminate passing people or vehicles from the image. This creates the impression of empty streets and squares without having to shut them off. ND filters also provide the ability to make an object stand out from a blurred background, even with an open aperture. Beyond photography gray filters also used in lighting technology to reduce the light from non-dimmable headlamps as needed.

buying Tips

The higher the above-described extension factor of a filter, the more opaque it is. For amateur photographers, ND 4X filters are usually sufficient to produce good flow effects. However, amateur photographers should put together a set of filters of different strengths to cope with the different lighting conditions and motifs. A major problem is the color shifts with strong filters (such as ND 1000X). Due to the higher exposure time, more light in the infrared range is left through the lens. As a result, the photographs taken often receive a reddish tint. The market already offers some ND filters with a minimal color cast.

The price alone does not necessarily determine the quality of a gray filter. Good filters affect the image and its colors only insignificantly. This can be seen but only in the field test. Only then does it become apparent that the use of an ND filter makes the image taken with a longer exposure time equal to a picture without a filter and a shorter exposure. Here, various reports from photographers and test reports give a very good insight into the different qualities.

Models and manufacturers

The market offers a very wide range of different manufacturers and their models. Among the established manufacturers include LEE, B & W, Singh Ray or Hoya, whose gray filters deliver good optical qualities, but are also more expensive. Thus, the Hoya HMC NDX8 not only offers high-quality and durable processing, but also correspondingly good image results, even if minimal red or blue stings are possible. B & W is one of the more expensive manufacturers. The comparatively high prices are also justified. The B & W gray filter MRC F-PRO offers not only a reduction of six glare levels, but also a blocking of UV radiation.

But there are also more and more cheap manufacturers, such as Haida, Cokin or Hitech. Especially Haida can convince with very good image results and barely noticeable discoloration. For example, the PRO II series MC Neutral neutral density ND1000 is almost unbeatable in its price range and can easily compete with the more expensive manufacturers.