How to calculate ND filter exposure
- Meter the scene without the filter, in manual or aperture priority, and note the shutter speed (for example 1/60).
- Type it in the first box and pick your ND filter. For stacked filters, add the second filter's stops in Extra stops.
- Set your camera to the new shutter time, using Bulb mode beyond 30 seconds.
- Press Start on the timer when you open the shutter.
ND filter strengths explained
ND filters are labelled three ways. ND8 is a factor (8× less light), 0.9 is the optical density, and both equal 3 stops. Each stop doubles the exposure time, so the new time is the old time × 2stops. Common results from a metered 1/60 s: ND8 → 1/8 s, ND64 → about 1 s, ND1000 (10 stops) → about 17 s, and a 15-stop ND32000 → about 9 minutes.
Use 3–6 stops to blur waterfalls and rivers or to shoot wide apertures in daylight, and 10 stops or more to smooth seas into mist and make clouds streak. Focus and compose before fitting a strong filter, since autofocus may not work through it, and cover the viewfinder to stop light leaking in. Strong filters often add a color cast; shoot RAW and correct white balance afterwards.
FAQ
How many stops is an ND1000?
About 10 stops, multiplying the exposure time by 1024.
What is the difference between ND8 and 0.9?
Nothing: ND8 is the filter factor and 0.9 the optical density. Both mean 3 stops.
How do I calculate stacked ND filters?
Add their stops. An ND8 (3) plus an ND64 (6) is 9 stops.