ND Filter Exposure Calculator

Check the exposure setup

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Setup preset:

Start from a practical camera scenario, then adjust the metered and target exposure values.

Exposure job:

Use still mode for long exposures; use video mode when preserving motion blur is the main constraint.

Metered shutter:

Enter seconds or pick a common camera shutter speed from the adjacent list.

Current aperture:

Use the f-number from the meter reading.

Target aperture:

Wide apertures in daylight usually require stronger ND.

Current ISO:

Keep this aligned with the meter reading.

Target ISO:

Changing target ISO changes the ND recommendation and the exported exposure notes.

Target shutter:

For water, clouds, traffic, or intentional blur, enter the final shutter time you want to hold.

Frame rate:

24 fps at 180 deg gives about 1/48 s; 30 fps gives about 1/60 s.

fps

Shutter angle:

Use 180 for standard motion blur or another angle for a deliberate look.

deg

Internal ND already in:

Set 0 unless the target camera setup already includes internal ND.

stops

Physical filter step:

Third-stop rounding is useful for cinema kits and variable ND markings; full stops match common fixed filters.

Stack strategy:

Controls the recommendation row; exact exposure math stays unchanged.

Variable ND range:

Use the labeled usable range from a variable ND before hard-stop or X-pattern artifacts.

to stops

Exposure bias:

Positive values add ND for a darker safety margin; negative values leave more light.

stops

Comfort shutter limit:

Used only for practical warnings in the guide rows.

Metric	Value	Use	Copy
{{ row.metric }}	{{ row.value }}	{{ row.use }}

Plan	Setting	Stop error	Use	Copy
{{ row.plan }}	{{ row.setting }}	{{ row.error }}	{{ row.use }}

Filter	Stops	Neutral shutter	Error	Note	Copy
{{ row.filter }}	{{ row.stops }}	{{ row.shutter }}	{{ row.error }}	{{ row.note }}

Chart renderer unavailable; use the Shutter Ladder table for the same filter-fit data.

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Neutral-density filters reduce the light reaching a camera without intentionally changing aperture, shutter time, ISO, framing, or color. Photographers use them when the metered exposure is too bright for the creative exposure they want: longer shutter times for water and clouds, wider apertures in daylight, or video motion blur that follows a chosen shutter angle.

ND planning is a stop calculation. One stop cuts transmission in half, two stops pass one quarter of the light, and ten stops pass about one thousandth. The same light cut may be printed as a stop count, an optical density, a filter factor, or a common label such as ND64 or ND1000, so a useful calculation should translate between those naming systems without hiding the exposure tradeoff.

Metered light passing through a neutral-density filter and reaching the camera as reduced light.

The result is a planning value, not a promise that the image will match perfectly. Real filters can add color shift, flare, vignetting, uneven variable-ND darkening, or exposure error from a meter reading that was already wrong.

How to Use This Tool:

Start from the metered camera setting, choose the exposure you want after the filter is fitted, then compare the exact stop count with practical filter choices.

Choose a Setup preset such as cinema wide-open daylight, drone 180-degree shutter, waterfall silk exposure, cloud streak long exposure, or wide-aperture portrait. Choose Custom when you want the entered values to stay untouched.
Select the Exposure job. Use Still photo target shutter when you already know the final shutter time. Use Video shutter angle when the target shutter should come from Frame rate and Shutter angle.
Enter the metered exposure with Metered shutter, Current aperture, and Current ISO. The shutter quick-pick list helps match common camera values such as 1/125 s, 1/30 s, 2 s, or 30 s.
Enter the target exposure with Target aperture, Target ISO, and either Target shutter or the video Frame rate and Shutter angle. The summary should update to a filter call, exact stops, pick error, target shutter, and light-pass percentage.
Set Internal ND already in if the camera or lens path already includes fixed filtration. Use Exposure bias only when you deliberately want a darker or brighter safety margin than the meter implies.
Choose the Physical filter step and Stack strategy. Full-stop rounding matches many fixed ND filters, third-stop and half-stop rounding suit finer kits, and the variable-ND range check tells you whether the exact stop count is inside the declared usable range.
If an input warning appears, check that shutter times, apertures, ISO values, frame rate, and shutter angle are greater than zero, and make sure the variable-ND maximum is not below its minimum. Read Exposure Brief first, then compare Filter Stack, Shutter Ladder, and Exposure Fit Map before choosing glass.

Interpreting Results:

Exact ND is the mathematical target after aperture, ISO, shutter time, internal ND, and exposure bias are accounted for. Practical pick is the usable filter suggestion after the selected rounding or filter strategy. The difference between them appears as stop error, where a positive error is darker than exact and a negative error is brighter than exact.

Do not treat a close stop match as an optical quality guarantee. A filter that lands within one third stop can still shift color, vignette on a wide lens, cause reflections, or show a variable-ND cross pattern near its extreme setting. Verify the final exposure with the camera histogram, waveform, false color, or a test frame when the shot matters.

Light pass: lower percentages mean heavier filtration. Around 0.1% is roughly a 10-stop ND1000 class result.
Optical density: density rises by about 0.3 per stop, so ND 1.8 is about six stops and ND 3.0 is about ten stops.
Filter factor: the exposure multiplier is 2 raised to the stop count, so eight stops is about 256x.
Shutter Ladder: use this table to see what each common filter would do to neutral shutter time and stop error.
Exposure Fit Map: the shaded center band marks roughly within one third stop of exact; points outside it need exposure compensation or a different filter plan.
Zero or no ND: the target setup is already at or darker than the metered exposure, so an external ND filter cannot solve that direction of exposure change.

Technical Details:

Neutral-density exposure math uses the same stop scale as aperture, shutter time, and ISO. A one-stop ND filter divides light by two. A two-stop filter divides light by four. Because the scale is logarithmic, filter factors multiply while stop counts add, which is why stacked filters can be planned by adding their stop values.

Exposure value condenses aperture, shutter time, and ISO into one scene-brightness comparison. The metered exposure and the target exposure are each converted to that scale. The required external ND is the difference between those values after subtracting any internal ND already committed to the target setup and applying any intentional exposure bias.

Formula Core:

The core calculation uses seconds for shutter time, aperture as an f-number, ISO as a numeric sensitivity value, and stop counts for filtration.

\begin{matrix} {EV}_{100} & = & \log_{2} (\frac{N^{2}}{t}) - \log_{2} (\frac{ISO}{100}) \\ t_{video} & = & \frac{angle}{360 fps} \\ S_{external} & = & {EV}_{metered} - ({EV}_{target} + S_{internal}) + S_{bias} \\ factor & = & 2^{S_{external}} \\ OD & \approx & 0.3 S_{external} \\ transmission & = & \frac{100}{factor} % \end{matrix}

ND exposure formula symbols
Symbol	Meaning	User-facing source
`N`	Aperture f-number.	Current aperture or Target aperture.
`t`	Exposure time in seconds.	Metered shutter, Target shutter, or video-derived target shutter.
`ISO`	Camera sensitivity setting used for the exposure comparison.	Current ISO or Target ISO.
`S`	Neutral-density strength in stops.	Exact ND, Internal ND already in, Exposure bias, and practical filter picks.
`OD`	Optical density label, approximately 0.3 per stop for photographic ND naming.	Optical density output.

For a video setup metered at f/8, 1/2000 s, ISO 100 and targeted at f/2.8, ISO 100, 24 fps, and a 180 degree shutter angle, the target exposure time is 180 / (360 x 24), or about 1/48 s. The metered exposure is about EV 17.0 and the target exposure is about EV 8.6, so the external ND target is about 8.4 stops. That is roughly OD 2.5, about a 340x filter factor, and about 0.29% transmission.

Filter naming and rounding:

Common filter labels mix several conventions. The stop count is the easiest value for exposure adjustment. Optical density is common in cinema and square-filter systems. Filter factor is common in still-photo charts. Printed labels such as ND64 and ND1000 usually refer to a factor rounded to a familiar product name.

Common ND filter naming relationships
Stops	Optical density	Filter factor	Approx. transmission	Common label
1	0.3	2x	50%	ND2
3	0.9	8x	12.5%	ND8
6	1.8	64x	1.56%	ND64
10	3.0	1024x	0.10%	ND1000 class
16.6	4.98	100000x	0.001%	ND100000 class

Rounding changes the filter recommendation, not the exact exposure math. Nearest third-stop and half-stop choices can produce labels based on optical density and factor when no common fixed label is exact. The single fixed filter choice searches common labels such as ND2 through ND100000. The two-filter stack searches common positive filters up to 10 stops each and chooses the pair with the smallest absolute stop error.

ND calculation boundary and validation rules
Boundary	Rule	Practical meaning
Required stops below zero	Exact external ND is clamped at 0 stops for display.	The target exposure needs less light reduction, not more external ND.
Required stops above the display cap	External ND is capped at 30 stops.	The requested setup is beyond normal photographic filter planning.
Variable ND range	Minimum must be less than or equal to maximum.	An inverted range blocks a usable variable-ND recommendation.
Video target shutter	Frame rate and shutter angle must be greater than zero.	At 24 fps and 180 degrees, the target shutter is about 1/48 s.
Fit-map center band	Stop error from -0.333 to +0.333 is inside the one-third-stop guide band.	Exposure compensation is usually small, but the camera still verifies the final image.

The neutral shutter shown in the ladder is the shutter time that would preserve the metered exposure if a particular common filter were used with the target aperture, target ISO, internal ND, and bias. It is useful for deciding whether to accept a nearby filter and trim shutter time, aperture, ISO, lighting, or variable-ND setting.

Accuracy and Safety Notes:

ND filter calculations assume the meter reading is reliable and the filter behaves neutrally across the visible spectrum. Real-world results can drift when light changes, when a camera uses nonstandard ISO behavior, when a filter has a color cast, or when stacked filters add reflections and vignetting.

Use the calculation for exposure planning, then verify with a test image, waveform, false color, or histogram.
Variable ND filters can become uneven near their strongest settings, especially with wide lenses or excessive rotation.
Ordinary photographic ND filters are not solar-viewing filters. Do not look directly at the sun through a camera viewfinder or filter unless the gear is specifically rated for safe solar observation.
No photo upload is needed because the calculation works from camera settings, not image files.

Worked Examples:

Wide-open video in bright daylight. A scene meters at f/8, 1/2000 s, ISO 100. Shooting at f/2.8, ISO 100, 24 fps, and 180 degrees gives a target shutter near 1/48 s. Exact ND lands around 8.4 stops, with Light pass near 0.29%. If Practical pick is slightly bright or dark, the Filter Stack stop error tells you how much to trim exposure.

Waterfall long exposure. A still-photo setup meters at f/11, 1/125 s, ISO 100, and the target is f/11, 2 s, ISO 100. The shutter change is almost eight stops, so Exact ND should sit near 8.0 stops and a common ND256 class filter is a natural first check. The Shutter Ladder helps confirm whether a nearby ND128 or ND400 choice would make the final shutter too short or too long.

Variable ND outside its marked range. A portrait target may need 6.2 stops while the entered variable-ND range is 2.0 to 5.0 stops. The Variable ND range row will show the target outside the usable range, even though a single fixed filter or two-filter stack may still be close. Do not force the variable ND past its marked limit just to match the number, because uneven darkening can become worse than a small exposure trim.

Troubleshooting an input warning. If the calculator asks you to check the setup after changing the variable-ND controls, look for a maximum value below the minimum. If video mode stops producing a meaningful target, check that Frame rate and Shutter angle are both greater than zero before reading Exposure Brief again.

FAQ:

Why does video mode ask for shutter angle instead of only shutter speed?

Shutter angle ties exposure time to frame rate. At 180 degrees, each frame is exposed for half of its frame interval, so 24 fps gives about 1/48 s and 30 fps gives about 1/60 s.

Should I buy the exact stop value or the practical pick?

Use Exact ND as the target and Practical pick as the physical starting point. If the pick error is small, the camera can often absorb it with a third-stop shutter, aperture, ISO, or lighting adjustment.

Why does the result sometimes say no external ND?

A zero-stop result means the target exposure is already at or darker than the metered setup after internal ND and bias are included. External ND can only reduce light, so fix the target shutter, aperture, ISO, or bias instead.

Can I trust a variable ND when it is in range?

The range check only compares stop strength. Inspect the image for cross-pattern darkening, color shift, and vignetting, especially near the strongest end of the variable ND or with wide-angle lenses.

Why am I getting an exposure setup warning?

The usual causes are a zero or negative shutter time, aperture, ISO, frame rate, or shutter angle, or a variable-ND maximum set below its minimum. Correct those fields before relying on Exposure Brief, Filter Stack, or Exposure Fit Map.

Glossary:

Neutral-density filter: A filter that reduces light before it reaches the camera while aiming to leave color and contrast neutral.
ND stop: A base-2 exposure step where each additional stop halves transmission.
Optical density: A logarithmic filter label; photographic ND naming commonly uses about 0.3 density per stop.
Filter factor: The exposure multiplier that matches the ND strength, such as 64x for six stops.
Transmission: The percentage of light that passes through the calculated external ND filter.
Shutter angle: A cinema-style way to express exposure time as a fraction of each video frame interval.
Stop error: The difference between a practical filter choice and the exact stop target.

References:

Understanding Neutral Density Filters, Edmund Optics.
B+W neutral density filters, Schneider-Kreuznach.
B+W ND Vario filter, Schneider-Kreuznach.
Panavision Millennium DXL2 operation guide, Panavision, 2020.
Essential Reference Guide for Filmmakers, Kodak.
Exposure value, Wikipedia.