Home › Photography & Optics › ND Filter Exposure Calculator

ND Filter Exposure Calculator

Computes the shutter speed needed after adding a neutral-density filter given in stops or as a filter factor (ND8, ND64, ND1000 ...), plus the filter's optical density and a table of resulting shutter speeds for common filters.

When to use

You know the correctly exposed shutter speed without a filter and want the exposure time with an ND filter, or need to convert between ND stops, filter factor and optical density.

Do not use when: The change comes from aperture or ISO rather than a filter (use equivalent-exposure), or you need the exposure value itself (use exposure-value).

Formula

stops = nd_stops or log2(nd_factor); new_shutter_seconds = base_shutter_seconds × 2^stops; optical_density = log10(2^stops)

Assumes the filter is neutral and the scene light is constant; a marketed 'ND1000' is 9.97 stops (2^10 = 1024). Exposures beyond about 30 s need bulb mode, and film needs reciprocity-failure compensation.

Inputs

Parameter	Type	Unit	Required	Description
`base_shutter_seconds`	number	s	yes	Exposure time in seconds. Enter fractions as decimals: 1/125 s = 0.008, 1/60 s = 0.016667, 1/1000 s = 0.001. Range: > 0, ≤ 86400
`nd_stops`	number	stops	no	Filter strength in stops (3-stop, 6-stop, 10-stop ...). Give this or nd_factor; when both are given nd_stops is used. Range: ≥ 0, ≤ 30
`nd_factor`	number		no	Filter factor as in the ND name: ND8 = 8, ND64 = 64, ND1000 = 1000 (stops = log2(factor)). Range: ≥ 1, ≤ 1000000000

Outputs

Output	Type	Unit	Description
`new_shutter_seconds`	number	s	base_shutter_seconds × 2^stops.
`new_shutter_text`	string		The same value as a fraction or seconds, e.g. '1/15 s' or '17.07 s'.
`stops`	number	stops	Light reduction in stops (log2 of the filter factor).
`nd_factor`	number		2^stops: how many times less light reaches the sensor.
`optical_density`	number		log10(filter factor): the ND value printed on some filters (0.9 = 3 stops, 3.0 = 10 stops).
`filter_table`	object	s	Resulting shutter speed in seconds for ND2, ND4, ND8, ND16, ND64, ND400 and ND1000 from the same base speed.

Example

1/60 s with a 10-stop filter: {"base_shutter_seconds":0.016667,"nd_stops":10} → {"new_shutter_seconds":17.067,"stops":10,"nd_factor":1024,"optical_density":3.01}

1/125 s with an ND8 filter: {"base_shutter_seconds":0.008,"nd_factor":8} → {"new_shutter_seconds":0.064,"stops":3,"optical_density":0.9,"new_shutter_text":"1/16 s"}

GET https://tttkmbb.com/api/v1/calculate/nd-filter-exposure?base_shutter_seconds=0.016667&nd_stops=10

Machine access

API: GET https://tttkmbb.com/api/v1/calculate/nd-filter-exposure (query parameters) or POST with a JSON body {"inputs": {...}}
Schema: https://tttkmbb.com/api/v1/calculators/nd-filter-exposure · Markdown: https://tttkmbb.com/photography/nd-filter-exposure.md · JSON definition: https://tttkmbb.com/photography/nd-filter-exposure.json
MCP: server https://tttkmbb.com/mcp, tool run_calculator with calculator_id="nd-filter-exposure"
OpenAPI operationId: calculate_nd_filter_exposure
Freshness: static. Authentication: none. Rate limit: fair use (see rate limits).

Sources

Wikipedia – Neutral-density filter (reference)
Wikipedia – Exposure value (reference)

FAQ

Is ND1000 the same as a 10-stop filter?

Almost: ND1000 reduces light 1000× = 9.97 stops, a true 10-stop filter 1024×; the 0.03-stop difference is far below camera exposure tolerance.

How do I read the optical-density marking?

Density d means a factor of 10^d: ND 0.3 = 1 stop, 0.9 = 3 stops, 1.8 = 6 stops, 3.0 = 10 stops (each 0.3 of density is one stop).

Related calculators

Equivalent Exposure Calculator — Compensate with aperture or ISO instead of shutter speed.
Exposure Value Calculator — Exposure value of the base setting.