Photography
ND filter exposure.
Meter the scene without the filter. Enter that shutter speed and the strength of your neutral density filter or stack. See the new shutter speed, the stops of light removed and how much light reaches the sensor.
Your numbers
Result
Fill the form and press Calculate.
Worked example
Metered 1/125 s, then a 10-stop filter: 1/125 × 210 = 1024/125 = 8.2 s. Choose "Filter factor" and 1000 instead (an ND1000) and the result is 1/125 × 1000 = 8 s, because 1000 is 9.97 stops, not exactly 10.
How it works
A filter that passes a fraction of light T needs the exposure time multiplied by 1/T. Stops are log base 2 of that factor, so new time = old time × 2stops. Optical density D gives transmittance 10−D, so stops = D / log10(2) = D ÷ 0.301; ND 0.9 is 2.99 stops, sold as 3. A filter factor F is log2(F) stops. Stacking filters adds their stops.
Filters rarely match their label exactly and may add a colour cast. Film can need extra time on long exposures (reciprocity failure), which this tool does not model. Digital cameras limit the longest timed exposure; beyond it use Bulb mode.
Sources and basis (checked 2026-10-05): Wikipedia: Neutral-density filter (transmittance = 10−d; ND 0.9 = 3 stops, ND 1.8 = 6 stops, ND 3.0 = 10 stops nominal). Arithmetic on the numbers you enter.
FAQ
How do I calculate shutter speed with an ND filter?
Multiply the unfiltered shutter time by 2 for every stop the filter removes. A 3-stop filter multiplies the time by 8, a 10-stop filter by 1024.
What is the difference between ND8, ND 0.9 and 3 stops?
They are three labels for about the same filter: factor 8, optical density 0.9 and three stops of light.
How many stops is an ND1000 filter?
A factor of 1000 is log2(1000) = 9.97 stops, usually rounded to 10 stops.
Can I stack two ND filters?
Yes. Stops add, so a 3-stop plus a 6-stop filter is 9 stops. Stacking can add vignetting and colour cast.
Should aperture and ISO change?
No. Hold them as metered; the filter is compensated by the longer shutter time alone.