A neutral density (ND) filter is a darkened piece of glass that reduces the light entering your lens without changing colours. It lets you use slow shutter speeds or wide apertures in bright scenes, which helps with silky water, moving clouds and soft backgrounds.
Understanding the Numbers
ND strength is expressed in different ways, and labels vary between makers. You may see optical density numbers, stops of light, or a factor such as ND8. The idea is the same: a stronger filter blocks more light. Check the maker’s guide for how it labels strength.
- One stop halves the light.
- Two stops leave one quarter.
- Three stops leave one eighth.
- Ten stops let through a tiny fraction, enough for very long exposures in daylight.
Fixed or Variable
A fixed ND filter has one strength and tends to be the most dependable. A variable ND lets you turn a ring to change strength, which is handy but can cause uneven darkening or colour shifts at the extremes. Always read the maker’s notes about limits.
Using One Step by Step
- Mount the camera on a tripod and compose without the filter.
- Focus, then switch to manual focus so it stays put.
- Attach the filter to the lens.
- Set the exposure mode and shutter speed for the effect you want.
- Take a test shot and check the screen.
- Adjust the shutter speed up or down until the brightness looks right.
Strong filters can make the viewfinder very dark, so compose first. Light can also leak in through an optical viewfinder during long exposures, so cover it if the camera maker advises.
Choosing a Strength
| Goal | Typical approach | Notes |
|---|---|---|
| Wide aperture in sun | Light to moderate ND | Keeps shutter in range |
| Soft water in daylight | Moderate to strong ND | Needs a tripod |
| Streaking clouds | Very strong ND | Exposures of minutes |
| Video with natural motion blur | Variable or fixed ND | Keep the shutter near twice the frame rate |
A worked example helps. Suppose a bright scene calls for a shutter speed that is too fast for the effect you want. Add a filter that removes some stops of light, and each stop doubles your shutter time: an exposure of one hundred twenty-fifth of a second becomes about one sixtieth with one stop, and so on. Many phone apps and online tables convert stops into shutter times, which saves arithmetic in the field. Always check the result on the screen and adjust.
FAQ
Will an ND filter change colours?
Good ones are close to neutral, but some add a slight tint that can be fixed in editing.
Do I need one for video?
Often yes. It lets you keep a natural shutter speed and wide aperture in bright light.
The Short Version
An ND filter lets you slow the shutter or open the aperture in bright light. Begin with a moderate strength, use a tripod, and learn to compensate exposure by stops.
