ND filter table
Every doubling of the filter factor costs one stop and doubles the exposure time. The table gives the stops, the filter factor, the optical density and what 1/125 s turns into for each common ND filter.
| Filter | Stops | Filter factor | Optical density | 1/125 s becomes |
|---|---|---|---|---|
| ND2 | 1 | 2× | 0.3 | 0.016 s |
| ND4 | 2 | 4× | 0.6 | 0.032 s |
| ND8 | 3 | 8× | 0.9 | 0.064 s |
| ND16 | 4 | 16× | 1.2 | 0.128 s |
| ND32 | 5 | 32× | 1.5 | 0.256 s |
| ND64 | 6 | 64× | 1.8 | 0.512 s |
| ND128 | 7 | 128× | 2.1 | 1.0 s |
| ND256 | 8 | 256× | 2.4 | 2.0 s |
| ND512 | 9 | 512× | 2.7 | 4.1 s |
| ND1024 | 10 | 1024× | 3.0 | 8.2 s |
| ND2048 | 11 | 2048× | 3.3 | 16.4 s |
| ND4096 | 12 | 4096× | 3.6 | 32.8 s |
| ND8192 | 13 | 8192× | 3.9 | 1 min 6 s |
Starting from a different shutter speed? Use the online calculator or the app itself, where you can stack up to five filters.
Reading off exposure times
The row is the shutter speed your camera suggests without a filter, the column is the filter you screw on. Past roughly 30 seconds you need bulb mode – and with it a timer.
| No filter | ND8 | ND64 | ND256 | ND1024 | ND4096 |
|---|---|---|---|---|---|
| 1/500 | 0.016 s | 0.128 s | 0.512 s | 2.0 s | 8.2 s |
| 1/250 | 0.032 s | 0.256 s | 1.0 s | 4.1 s | 16.4 s |
| 1/125 | 0.064 s | 0.512 s | 2.0 s | 8.2 s | 32.8 s |
| 1/60 | 0.133 s | 1.1 s | 4.3 s | 17.1 s | 1 min 8 s |
| 1/30 | 0.267 s | 2.1 s | 8.5 s | 34.1 s | 2 min 17 s |
| 1/15 | 0.533 s | 4.3 s | 17.1 s | 1 min 8 s | 4 min 33 s |
| 1/8 | 1.0 s | 8.0 s | 32.0 s | 2 min 8 s | 8 min 32 s |
| 1/4 | 2.0 s | 16.0 s | 1 min 4 s | 4 min 16 s | 17 min 4 s |
| 1/2 | 4.0 s | 32.0 s | 2 min 8 s | 8 min 32 s | 34 min 8 s |
| 1 s | 8.0 s | 1 min 4 s | 4 min 16 s | 17 min 4 s | 68 min 16 s |
The formula behind it
New exposure time = original time × filter factor. An ND64 stretches 1/125 s to 1/125 × 64 = 0.512 s. In stops: each stop doubles the time, and six stops are a factor of 64.
Optical density is the same value written logarithmically. A filter with a density of 3.0 swallows ten stops – that is the familiar ND1024, which many makers label ND1000.
Which filter for what?
- ND8 to ND64: moving water in a creek, a touch of motion blur, video on the 180-degree rule under an overcast sky.
- ND256 to ND1024: glassy water at the coast, drifting clouds, making people vanish from a busy square.
- ND4096 and stronger: long exposures in full sun, architecture without passers-by.
Stacking filters
Screw-in filters of the same diameter stack on top of each other, and most holders take several square filters at once. Stops add up, factors do not: ND8 plus ND64 is 3 + 6 = 9 stops, a factor of 512. The FAQ covers the rest.