ND Filter Calculator

What it does

Converts your base (no-filter) shutter speed into the equivalent shutter speed once an ND (neutral density) filter is attached — each stop of ND filtration doubles the required exposure time, since the filter is blocking that fraction of the light.

What you'll need

• Your metered shutter speed without the filter attached.
• The ND filter's strength, either by its common name (e.g. ND1000) or the stop count it corresponds to.

Steps

1. Meter your shot normally, without the filter, and note the shutter speed.
2. Enter that as the base shutter speed.
3. Pick your filter strength.

Reading the result

The result is the shutter speed to dial in once the filter is on, to get the same exposure the base reading gave you. For speeds beyond about 1 second you'll typically need Bulb mode and a stopwatch or intervalometer rather than your camera's normal shutter dial.

Tips

• Very long results (many seconds to minutes) are common with strong ND filters like ND1000 in daylight — that's expected, it's the whole point of the filter for long-exposure water/cloud/sky shots.
• Re-meter after attaching very strong filters if your camera's metering can't see through them — use this calculator's math instead of relying on live metering in that case.

What is an ND filter?

A neutral density (ND) filter is a darkened piece of glass or resin that mounts in front of your lens and reduces the amount of light entering the camera evenly across the visible spectrum — the “neutral” part means it darkens without shifting colour, unlike a warming or coloured filter. It doesn't change anything else about the shot; it just buys you a longer shutter speed (or wider aperture) than the available light would otherwise allow.

Why photographers use it

Without an ND filter, bright daylight forces a fast shutter speed just to avoid overexposing — which rules out any of the classic long-exposure looks. An ND filter lets you shoot a multi-second (or multi-minute) exposure in full sun: moving water turns to mist, clouds streak across the sky, a crowded street empties of anyone who didn't stand still. It's also useful for a much smaller reason day to day — keeping a wide aperture available for shallow depth of field in bright light without blowing out the shot.

Which ND filter strength should I choose?

ND2-ND8 (1-3 stops) is for subtle daylight control — holding a wide aperture in bright sun, or gentle video exposure work. ND64-ND100 (roughly 6 stops) is the sweet spot for waterfalls and rivers in daylight: enough to soften water into that classic silky texture while keeping the exposure to a few seconds, not minutes. ND1000 (roughly 10 stops) is for full-blown long exposure in broad daylight — minutes-long shutter speeds, streaking clouds, glassy seas, crowds vanishing from a frame. ND2000-ND32000 (11-15 stops) push into extreme territory — multi-minute or even multi-hour exposures in full daylight, mainly for deliberately dramatic cloud/sky motion or genuinely disappearing crowds over a long sitting; at that strength, reciprocity and sensor-heat effects (see the mistakes below) become a real factor, not just a footnote. Variable ND filters (two rotating polarizing elements) trade a bit of image quality — a possible colour cast or dark X-pattern at their most extreme setting — for the convenience of one filter covering a wide stop range instead of a filter case full of fixed ones.

Common mistakes

• Trusting the camera's live meter through a very strong filter. ND1000 and similar block so much light that through-the-lens metering often can't read the scene at all, or reads it wrong. Meter without the filter, use this calculator to get the adjusted shutter speed, then dial that in manually.
• Attaching the filter before focusing. autofocus needs light to work, and a strong ND filter starves it — the camera will hunt and fail. Compose and focus first, switch to manual focus so it can't refocus itself, then attach the filter.
• Treating the calculated shutter speed as exact for very long exposures. sensor heat and reciprocity effects can shift real-world exposure slightly on shots beyond a couple of minutes. Check a test frame's histogram on very long exposures rather than trusting the math blindly.
• Confusing stop count with density-number labelling when buying. "ND1000" and "10-stop" are the same filter; some manufacturers label by optical density (e.g. "3.0") instead of the factor or stop count, which trips people up when comparing filters across brands.
• Skipping a solid tripod because the filter is the star of the plan. almost every strong-ND shot is also a long-exposure stability problem — a lightweight tripod in coastal wind will blur the whole frame regardless of how correct the ND math is.

Example settings

FAQ

Why is it called "neutral" density?

Because it darkens the image evenly across all colours, without adding a tint — a genuine ND filter shouldn't shift your white balance, unlike a warming, cooling, or graduated colour filter.

Can I stack two ND filters together?

Yes — their stop counts add (their factors multiply), so an ND8 plus an ND64 behaves like roughly a 9-stop filter. Stacking many filters can introduce vignetting or a colour cast at extreme densities though, so it's usually better to own one strong filter than to stack several.

Why does autofocus stop working once the filter is on?

Very dark filters don't let enough light through for the autofocus system to detect contrast or phase difference. Focus (and switch to manual focus) before attaching the filter, not after.

What is a variable ND filter?

Two rotating polarizing elements that let you dial in a continuously adjustable density instead of buying separate fixed-strength filters. Convenient, but many show a visible dark X-pattern or colour cast at their darkest setting — check reviews for your specific model before relying on the extreme end.

Do I need a tripod for every ND filter?

For the 1-3 stop range, often not — shutter speeds stay fast enough to handhold. Once you're into multi-second or multi-minute territory, yes — any handheld movement will blur the whole frame at those speeds.