How do I calculate shutter speed with an ND1000 filter?
Multiply your correctly metered shutter speed (without the filter) by 1024 — 2 to the 10th power, since ND1000 represents 10 stops of light reduction. A 1/200s metered exposure becomes roughly 5.1 seconds with an ND1000 attached; a 1/500s metered exposure becomes roughly 2 seconds; a 1/125s metered exposure becomes roughly 8.2 seconds.
Why 1000 Actually Means 10 Stops
ND1000 is named for its density factor — the scene appears 1000 times darker through the filter — not its stop count directly. Converting requires log base 2 of 1000, which comes out to 9.97, rounded to a clean 10 stops by every manufacturer rather than an awkward fractional number. 2^10 = 1024, which is why the actual multiplier used in practice (1024x) is very slightly higher than the filter's nominal 1000x rating — a difference small enough to ignore in the field.
The Practical Field Method
Meter your scene normally without the filter attached (most cameras can't autofocus or accurately meter through an ND1000 once it's on), note the shutter speed at your chosen aperture and ISO, then multiply by 1024 — or use the simpler shortcut of counting 10 full stops slower on your shutter speed dial or a smartphone long-exposure calculator app, which many photographers find faster in the field than mental multiplication.
Get the exact corrected shutter speed for your own metered exposure in the Exposure Triangle Solver.
Frequently Asked Questions
Can my camera meter accurately with an ND1000 already attached?
Usually not reliably — the filter blocks too much light for most camera meters and autofocus systems to work through directly, which is why the standard practice is to meter and focus first, then attach the filter and apply the calculated shutter-speed correction manually.
Do I need to worry about reciprocity failure with an ND1000 on a digital camera?
No — reciprocity failure is a film-specific phenomenon where a film stock's effective sensitivity drops at long exposure times; digital sensors don't exhibit the same effect, so an ND1000's shutter-speed math holds accurately even at exposures of several minutes.