ND8: three stops
The ND8 is the gentlest of the common neutral density filters. It swallows three stops and stretches the exposure by a factor of eight: 1/125 s becomes 1/15 s. That sounds like very little, and it is exactly why most people reach for it more often than for any other. It changes the picture without forcing it into a long exposure.
- Stops3
- Filter factor8×
- 1/125 s becomes0.064 s
What this strength is good for
- Moving water in a creek: Between 1/15 and 1/4 of a second water gains texture and direction while still reading as water. Go further and you get fog instead of a stream, which is a matter of taste rather than technique.
- Video on the 180-degree rule: This is the most important use. For natural motion blur the shutter speed should be roughly double the frame rate, so 1/50 s at 25 fps. On an overcast day with the aperture open, an ND8 is enough to get there.
- Wide apertures in sunlight: A portrait at f/1.8 on a bright afternoon runs past the fastest shutter speed many cameras offer. Three stops bring the exposure back into range without giving up the shallow depth of field.
Calculating with ND8
Pick a shutter speed. The fields are preset to ND8.
hours : minutes : seconds : milliseconds
Exposure times with ND8
On the left the speed your camera suggests without a filter, on the right what it becomes.
| No filter | With ND8 |
|---|---|
| 1/500 | 0.016 s |
| 1/250 | 0.032 s |
| 1/125 | 0.064 s |
| 1/60 | 0.133 s |
| 1/30 | 0.267 s |
| 1/15 | 0.533 s |
| 1/8 | 1.0 s |
| 1/4 | 2.0 s |
| 1/2 | 4.0 s |
| 1 s | 8.0 s |
What to watch for
- A tripod is still optional: 1/15 s is often holdable with a steady hand and stabilisation. Past about half a second it is not, and then you need a tripod that also stands up to wind.
- Practically no colour cast: At three stops even inexpensive filters show almost no tint. That changes noticeably once you move to the strong ones.
- Stacking rarely pays here: Two ND8 filters add up to six stops, which is an ND64, but also two more glass surfaces for stray light to bounce around in. If you regularly need six stops, a single ND64 is the better buy.
As the only filter in the bag the ND8 is too weak for glassy water, but as a companion it is the one that gets used most. Anyone shooting video will rarely take it off again.
The other strengths
Not sure which strength yet? Which ND filter? works from the subject to the number of stops.
Every value from ND2 to ND8192 is in the ND filter table, and the FAQ answers the common questions.