ND Exposure Calculator
Enter your metered shutter speed (without an ND filter), then add your filter value. The tool returns your new shutter speed for long-exposure photography.
What is a neutral density filter?
A neutral density (ND) filter is a darkened optical filter that reduces the amount of light entering your camera lens. It does this without (ideally) changing color. In practical photography, ND filters let you use slower shutter speeds or wider apertures in bright conditions.
Think of an ND filter like sunglasses for your camera. The scene brightness stays the same, but your camera can expose for longer.
Why use an ND filter calculator?
Once you add an ND filter, your original meter reading no longer applies. If your base exposure is 1/125 second and you add a strong filter like a 10-stop ND, the new shutter speed jumps to several seconds. Calculating that quickly in the field can be annoying, especially when lighting changes fast.
An ND calculator removes the guesswork and gives you a reliable shutter speed target.
How the math works
Every full stop of light reduction doubles exposure time:
- +1 stop = 2× longer shutter
- +2 stops = 4× longer shutter
- +3 stops = 8× longer shutter
Formula used by this calculator:
new shutter = base shutter × 2stops
Example: base shutter is 1/60 sec and filter is 6 stops.
New shutter = 1/60 × 26 = 1/60 × 64 = 1.07 sec
ND naming systems (and how to convert)
1) Stops
This is the most intuitive system in photography. A 10-stop filter reduces light by 10 stops.
2) Filter factor / ND number
Common labels include ND8, ND64, ND1000. These indicate light reduction factors.
- ND8 ≈ 3 stops
- ND64 = 6 stops
- ND1000 ≈ 10 stops
3) Optical density (OD)
Used by many manufacturers, especially in cinema and video workflows.
- OD 0.3 = 1 stop
- OD 0.9 = 3 stops
- OD 1.8 = 6 stops
- OD 3.0 = 10 stops
This calculator accepts all three systems and shows equivalents in the result.
Practical shooting tips for long exposures
- Use a sturdy tripod. Small vibrations become obvious at multi-second exposures.
- Turn off lens stabilization when camera is tripod-mounted (unless your lens manual says otherwise).
- Use a remote release or camera timer to reduce shake from pressing the shutter button.
- Cover the viewfinder on DSLRs to prevent light leak during long exposures.
- Shoot RAW when possible; it helps recover highlights and correct color cast from strong ND filters.
When you may need Bulb mode
If your calculated shutter speed exceeds your camera’s standard maximum (often 30 seconds), switch to Bulb mode. In Bulb mode, the shutter stays open as long as the trigger is held (or until a programmed interval ends).
This calculator warns you when your result is long enough that Bulb mode is likely needed.
Example scenarios
Waterfall smoothing in daylight
Metered shutter: 1/30 sec. Add 6-stop ND.
Calculated shutter: ~2 sec. Result: smooth, silky water and preserved highlights.
Cloud streaks over coastline
Metered shutter: 1/125 sec. Add 10-stop ND.
Calculated shutter: ~8 sec. Result: motion in cloud texture and soft water.
Street scene with moving people removed
Metered shutter: 1/15 sec. Add 10-stop ND.
Calculated shutter: ~68 sec. Result: stationary architecture remains while moving subjects fade out.
Final thoughts
ND filters open creative options that are impossible at normal shutter speeds in bright light. Whether you shoot landscapes, architecture, seascapes, or urban scenes, accurate exposure math is essential. Use the calculator above before each shot, then refine with histogram checks and test frames for best results.