ND Filter Calculator
Your new shutter speed after adding a neutral density filter.
Results
- New shutter speed
- 17s
- Nearest setting on your camera
- 15s
Set this as your new shutter speed after attaching the filter, keeping aperture and ISO unchanged.
The closest speed on the standard third-stop dial. Past 30 seconds the ladder runs out and you'll need bulb mode with a remote release.
How it works
A neutral density filter cuts light without changing colour, letting you use shutter speeds or apertures that daylight would otherwise make impossible. It is how you get silky water in the middle of the afternoon, or shoot wide open in bright sun.
Each stop of density doubles the exposure time needed. A 10-stop filter multiplies it by 1024, turning a 1/60 second exposure into roughly 17 seconds, which is why strong ND filters push you into territory where your camera's 30 second limit and then bulb mode become the constraint.
Work in this order: meter and compose without the filter, since a 10-stop is too dark to focus or even see through, then lock focus to manual, fit the filter, and dial in the time this gives you. Above 30 seconds you will need bulb mode, a remote release, and a way to keep stray light out of the viewfinder.
The formula
t₂ = t₁ × 2^stops
t₁ is the metered time without the filter and stops is the filter's density. ND numbers are the light transmission divider, so ND1000 blocks about 2^10 and is sold as a 10-stop.
Frequently asked questions
- Why is ND1000 called 10 stops when 2^10 is 1024?
- ND1000 is a rounded trade name. The true density is about 9.97 stops, which the calculator uses. The difference is far too small to see.
- Can I stack ND filters?
- Yes, and their stops simply add: a 6-stop plus a 3-stop gives 9. Stacking risks vignetting on wide lenses and can introduce colour casts, so a single stronger filter is usually cleaner.
- How do I focus through a 10-stop filter?
- Focus first without it, then switch the lens to manual so autofocus cannot hunt when you fit the filter and the view goes black.
- Do ND filters affect depth of field?
- No. They only reduce the amount of light, so aperture, and therefore depth of field, is unchanged. That is the entire point of using one.