Three ways manufacturers label ND filters
- ND number (e.g. ND8): a multiplier — how many times longer the exposure becomes. ND8 multiplies exposure by 8, which is 3 stops.
- Stops: how many stops of light the filter blocks. ND8 = 3 stops.
- Optical density: a logarithmic value where each 0.3 corresponds to 1 stop. ND8 = OD 0.9.
Shutter compensation
If your unfiltered exposure is 1/250 s and you stack a 10-stop ND, your new shutter time is 1/250 × 210 = 4.1 s. Use the helper above to get the exact value for any base shutter and any stop count.
Common ND uses
- ND8 (3 stops) — wide aperture in bright light, slight motion blur on water.
- ND64 (6 stops) — visible cloud streaks, smooth water in mid-day light.
- ND1000 (10 stops) — long-exposure landscapes; classic 30-second seascape.
- ND32000 (15 stops) — solar eclipse photography (with proper safety filter).
FAQ
Can I stack multiple ND filters? Yes — stops simply add. Stacking ND8 + ND4 gives 5 stops total.
Will an ND filter affect colour? Cheap ND filters can introduce a colour cast (often magenta or green). Brand-name filters are usually neutral within ±100 K.