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A neutral density filter or ND filter is a filter that reduces the intensity of all wavelengths of light equally. ND filters do not change the hue of a color rendition.
Why would you use an ND filter? Well generally speaking you use them when you want to lower the intensity of light in a situation. Why would you want to do this? Simply put, if a scene is too bright you can slap on an ND filter and you now have a much less bright scene.
Have you ever wanted to show motion or get a nice blue effect? ND filters are great for this. You know those photos with blurred out waterfalls like this:
https://www.flickr.com/photos/vinothchandar/8157323452/ photo by vinothchandar
These are generally shot with an ND filter. By using the ND filter you can shoot much longer exposures because there is less light entering through your lens.
There are various types of ND filters. There are the screw on type where you match the size and threading on the front of your lens to the filter. There are also square bracket mounts and that you screw onto your lens. Basically you mount a holder onto your lens and then just slide the filter in. This system is nice because you don’t have to have the exact same filter size as each lens you have.
Here are some more great videos on this topic:
Related Pages:
- You can check prices and buy ND filters here.
- ND Filters Wikipedia.
- More photography resources.
- Photography glossary.
Understanding ND Filter Strengths
ND filters are rated by how much light they block. A 1-stop ND filter (ND2) cuts the light in half. A 3-stop ND filter (ND8) reduces light to one-eighth of its original intensity. A 6-stop (ND64) and 10-stop (ND1024) filter are popular choices for daytime long exposures. The higher the stop rating, the longer your shutter speed can be. A 10-stop ND filter in bright daylight can turn a 1/125 second exposure into roughly an 8-second exposure, enough to blur water into a smooth, silky surface.
Choosing the Right ND Filter Type
Circular screw-on filters attach directly to the front of your lens. They are compact, simple to use, and less prone to light leaks. The downside is that you need a different filter diameter for each lens, although step-up adapter rings can help. Square and rectangular filter systems use a holder that mounts to the lens, and you slide the filter into the holder. This system is more versatile because one filter fits multiple lenses, and you can stack filters or use graduated ND filters that darken only part of the frame.
When to Use ND Filters
Landscape photography is the most common application. Smoothing out ocean waves, rivers, and waterfalls requires shutter speeds of several seconds or more, which is impossible in daylight without an ND filter. Architectural photographers use ND filters to remove moving people from busy scenes during long exposures. Portrait and video shooters use light ND filters to maintain a wide aperture for shallow depth of field in bright conditions where the shutter speed would otherwise be too fast.