The short version
- Each stop of ND doubles the shutter time: new time = old time × 2^stops.
- ND8 = 3 stops, ND64 = 6 stops, ND1000 = 10 stops, ND32000 = 15 stops.
- Optical density 0.3 equals one stop: a 0.9 filter is 3 stops, a 3.0 filter is 10.
- Past 30 seconds, switch to Bulb mode and time the exposure.
Last updated · Exposure Triangle Simulator editorial team · How we test
What an ND filter does
A neutral density filter is dark glass that reduces all colors of light equally. It lets you use a slow shutter speed or a wide aperture in bright light without overexposing. Typical uses: smooth waterfalls and seas, streaking clouds, people vanishing from busy squares, and shooting video at f/1.8 in daylight.
To see what a slow shutter does to motion, the shutter speed lesson opens the camera simulator with a moving car.
ND filter chart
| Filter name | Optical density | Stops | Light passed | 1/125 s becomes |
|---|---|---|---|---|
| ND2 | 0.3 | 1 | 50% | 1/60 s |
| ND4 | 0.6 | 2 | 25% | 1/30 s |
| ND8 | 0.9 | 3 | 12.5% | 1/15 s |
| ND16 | 1.2 | 4 | 6.25% | 1/8 s |
| ND64 | 1.8 | 6 | 1.6% | 1/2 s |
| ND1000 | 3.0 | 10 | 0.1% | 8 s |
| ND32000 | 4.5 | 15 | 0.003% | 4 min 22 s |
Filter names use the light reduction factor (ND8 cuts light to 1/8). Some brands label by stops ("10-stop") or density ("0.9"). They describe the same thing.
How to shoot a long exposure with an ND filter
- Put the camera on a tripod and compose.
- Without the filter, set ISO 100 and your aperture (f/8–f/11), and find the correct shutter speed.
- Focus, then switch the lens to manual focus. Autofocus struggles through a dark filter.
- Screw on the filter and set the new shutter speed from the calculator.
- Cover the viewfinder (on DSLRs) so light doesn't leak in, and use a remote or the 2-second timer.
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Frequently asked questions
What does ND1000 mean?
The filter reduces light by a factor of 1,000, which is 10 stops. A 1/125 s exposure becomes 8 seconds.
How do you calculate ND filter exposure time?
Multiply the shutter time without the filter by 2 raised to the number of stops. 1/60 s with a 6-stop filter is 1/60 × 64 ≈ 1 second.
What ND filter should I buy first?
A 6-stop (ND64) for flowing water and a 10-stop (ND1000) for long daylight exposures cover most needs. A variable ND is popular for video.
Do ND filters change colors?
Good ones barely do. Cheaper strong filters can add a color cast, often magenta or blue, which you can correct with white balance.