An ND, or neutral density, filter is a dark piece of glass that reduces light without changing color. Mount it, frame and focus first if the filter is very dark, then set a longer shutter speed or a wider aperture than daylight would normally allow.
Why Use One
In bright light, a normal exposure uses a fast shutter speed. That freezes motion. If you want moving water to look like mist, clouds to streak, or a crowd to blur, you need a slow shutter. The ND filter makes that possible without overexposing. It also lets you use a wide aperture for soft backgrounds under strong sun, or keep a natural shutter speed when shooting video.
Know the Strengths
Filter strength is described in stops of light removed. Check the maker’s marking, since labels vary between systems.
| Stops | Light reduced to | Typical use |
|---|---|---|
| 3 stops | One eighth | Gentle blur on waterfalls in shade |
| 6 stops | One sixty-fourth | Smooth water in daylight |
| 10 stops | About one thousandth | Long exposures of clouds and sea |
Step by Step for a Long Exposure
- Put the camera on a tripod and compose the scene.
- Focus with the filter off or in live view, then switch autofocus to manual so it does not shift.
- Fit the filter and shield the viewfinder if your camera has an optical one, since light can leak in.
- Meter without the filter, then add the stops. For instance, 1/60 second with a 6-stop filter becomes about one second.
- Use a remote release or timer. Take a frame and check the screen.
- Adjust the time up or down until the motion looks the way you want.
Common Problems
- Color cast: very dark filters may add a slight tint. Correct it with white balance or editing.
- Soft focus: the camera cannot focus through a dark filter, so lock focus first.
- Light leaks: cover the viewfinder or use the built-in shutter on some cameras.
- Vignetting: thick filters on wide lenses can darken corners.
Practice on a simple scene first, such as a stream or a flag in the wind. Take a handful of frames at different times, compare them on a larger screen, and note which duration gives the look you like. That record becomes your own guide for later outings.
FAQ
What is the difference between ND and polarizing filters?
An ND filter reduces all light evenly. A polarizing filter blocks reflected light and also loses some brightness. They do different jobs and can be combined.
Which strength should I carry first?
A medium strength around six stops covers many daylight cases. Add a darker one if you plan long exposures at midday.
The Short Version
An ND filter lets you use slow shutter speeds or wide apertures in bright light. Focus before fitting dark filters, meter without them, then add the stops. Use a tripod and a remote release for clean results.
