Filter This: The Indispensable ND Filter

One of the early lessons I learned in my photographic journey was to pay attention to the “small stuff.” It is a piece of advice that I often share in response to the increasingly popular question: “What accessories should I consider getting for my H(d)SLR?” In the quest to get the perfect tripod, shoulder stabilizer or viewfinder accessory, an accessory which is often overlooked is a filter, and more specifically, a neutral density or ND filter. These gray, filters are all about exposure control: A neutral density filter effectively reduces the amount of light which hits the camera sensor. In still photography, that light reduction translates into longer exposures(shutter speed adjustment,) and the ability to blur motion such as waterfalls, currents and waves. For still photography as well as motion capture, the reduction in light can translate into the ability to shoot with larger apertures in order to obtain a shallower depth of field, a reduction in scene contrast, and/or the ability to reduce the risk of overexposure. If you are planning on shooting motion outdoors in bright light or shooting scenes with highly reflective materials in them such as sand and snow, or steel and glass structures, consider ND filters, H(d)SLR essential accessories.

The amount of light reduction that a ND filter facilitates depends on the strength of the filter you use. Different manufactures utilize different designation for filter strength. They are commonly expressed in "density value," "filter factor," or f-stops.

- A density value of .3 equals a filter factor of 2 which equals one stop.
- A density value of .6 equals a filter factor of 4 which equals two stops.
- A density value of .9 equals a filter factor of 8 which equals three stops.

Using a one stop ND filter will result in 50% of the original light intensity being transmitted to the camera sensor; a two stop ND filter results in 25% of the original light intensity being transmitted to the sensor; and a three stop ND filter results in 12.75% of the original light intensity being picked up by the camera sensor. A true ND filter will not alter color balance, as it is color indifferent or neutral. The the filter strenghts listed above should be more thatn adequate to handle the typical photographers needs, there are stronger ND filter available for more specialized usages.

Neutral density filters are commonly used in video capture. There are several brands of camcorders that have ND filters built into the camera. With professional cameras, you will often see them seated in the matte box (lens hood equivalent) apparatus filter holder if a scene calls for them.

If you are going to use neutral density filters, on your H(d)SLR, you may want to disable auto ISO, in order to have the greatest control of the exposure as well as the results. You should consider buying the best filters you can afford. At the very least, consider multi-coated filters, as the coatings reduce reflections and make it less likely that your captures will experience ghosting and flare. Several manufacturers offer filters for high definition capture as well. Tiffen, Schneider, Hoya, Singh Ray and Cokin are among the most popular filter manufacturers and these companies make ND filters in various strengths and sizes. While I carry a one stop and a two stop filter in my camera bag, if came down to having to carry only one ND filter, the two stop filter would be my choice.

ND filters are a small item, that can make a big difference!

To view the current issue of "Outfitting Your H(d)SLR" click on the embedded magazine below.

"Outfitting Your H(d)SLR " a new resource for those shooting motion and stills

I am pleased to bring you our inaugural resource for H(d)SLR users, "Outfitting Your
H(d)SLR". The guide which will be published quarterly, is intended to provide information to those seeking to add accessories to their cameras to enhance the motion capture experience. I hope you find it informative and useful!
Byron

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