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Neutral Density Filter Stops Calculator

Work out neutral density filter stops instantly with clear inputs, formula shown and shareable results.

About Neutral Density Filter Stops Calculator

An ND factor of x reduces light by log2(x) stops, so the shutter speed must be multiplied by that same factor to keep the exposure unchanged. An ND64 is six stops, turning 1/125 into half a second, which is exactly what makes daylight long exposures of moving water possible.

Formulas

Stops

stops = log2(ND factor)

New shutter speed

new time = base time x ND factor

Worked example

With the default values below, Neutral Density Filter Stops Calculator returns Stops of light reduction of 6.000. Change any input above and every figure here is recalculated in your browser.

Inputs used

ND filter factorminimum 1 x
64 x
Shutter speed without the filterminimum 0 s
0.008 s

Results

Stops of light reduction
6.000
Shutter speed with the filter
0.5120 s
Exposure time to set
1/2 s
Light transmitted
1.5625%

Step by step

  1. 1Values used
  2. 2Stops
  3. 3New shutter speed
  4. 4Stops of light reduction= 6.000
  5. 5Shutter speed with the filter= 0.5120 s
  6. 6Exposure time to set= 1/2 s
  7. 7Light transmitted= 1.5625

Assumptions and limits

  • The result is derived only from the 2 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is the Neutral Density Filter Stops figure worked out?

stops = log2(ND factor). An ND factor of x reduces light by log2(x) stops, so the shutter speed must be multiplied by that same factor to keep the exposure unchanged.

Why does this matter?

An ND64 is six stops, turning 1/125 into half a second, which is exactly what makes daylight long exposures of moving water possible.

What do I need to enter?

Enter nd filter factor, shutter speed without the filter. The defaults shown are a realistic worked example — swap in your own figures to get a result you can use.

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