Free Online Tool · Deutsche Version
ND Filter
Calculator.
Enter your base exposure, pick the ND filter — and the calculator instantly shows the new exposure time. Works for two stacked filters too.
Base exposure time without filter
ND Filter
New exposure time
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What is an ND filter?
An ND filter (Neutral Density filter) is an evenly darkened piece of glass that screws onto the lens or slots into a filter system. It reduces the incoming light without shifting colors — hence "neutral".
That sounds simple, but it opens up enormous creative possibilities: with an ND filter you can shoot at f/1.4 wide open even in bright sunshine, or take a 30-second long exposure in the middle of the day — effects that would be technically impossible without a filter.
The number after "ND" indicates the light-absorption factor. ND8 lets through only 1/8 of the light, ND1000 only 1/1000. To keep the exposure the same, the camera needs to expose correspondingly longer — which is exactly what our calculator above works out.
Memory trick: Every doubling of the ND factor equals one stop and doubles the exposure time. ND8 → ND16: one stop more, expose twice as long.
Which ND filter do I need, and when?
Choosing the right gray filter depends on the effect you're after and the available brightness. As a rule of thumb: the brighter it is and the longer the desired exposure time, the stronger the filter needs to be.
| Filter | Factor / stops | Typical use | Effect |
|---|---|---|---|
| ND2–ND4 | 2–4× / 1–2 stops | Portraits in sun with a wide-open aperture | Wide aperture without overexposure |
| ND8 | 8× / 3 stops | Waterfalls, streams under overcast skies | First light motion blur in water |
| ND64 | 64× / 6 stops | Long exposure in daylight | Silky water, soft clouds (1–10 sec.) |
| ND1000 | 1000× / 10 stops | Strong long exposure during the day | 30 sec.+ in daytime, people vanish |
| ND4000 | 4000× / 11.9 stops | Extreme long exposure, architecture | Multi-minute exposures in bright daylight |
| ND64000 | 64000× / 16 stops | Day-to-night effects, hour-long exposures | Completely motionless image, stars in daylight |
Stacking ND filters
If you don't have the exact right single filter on hand, you can combine two ND filters — that's called stacking. The factors multiply:
- ND8 + ND8 = ND64 (6 stops)
- ND8 + ND64 = ND512 (9 stops)
- ND64 + ND1000 = ND64,000 (16 stops)
The calculator supports exactly that: enable "Add second filter" and choose both filters — the result is calculated instantly.
Careful when stacking: cheap filters can cause vignetting (dark corners) or slight color casts when stacked. Use thin "slim" filters where possible, or high-quality systems like Lee, Kenko or B+W. Stacking two quality filters is almost always better than a single cheap one.
Long exposure photography in Stuttgart: locations and tips
Stuttgart offers fantastic opportunities for long-exposure photography — and ND filters play a central role. Here are a few top spots:
- Schlossplatz at night: the fountains and the illuminated Old Castle tower are perfect for long exposures. Without an ND filter you'll need dusk or night for this. With an ND1000 you can capture the silky fountain jets even during the day. More on this in our German-language night photography guide for Stuttgart.
- Neckar river at Bad Cannstatt and Münster: the locks and the river offer calm, flowing water — ideal for an ND64 or ND8 under overcast skies. Half a second to two seconds is enough for the silky effect.
- TV tower and Birkenkopf viewpoint: hour-long exposures from the TV tower with an ND64000 turn the Stuttgart basin into a dramatic light painting. Ideal for dawn and blue hour.
- Lake Böblingen and the Fasanenhof ponds: calm water surfaces for reflection shots — an ND8 is often enough to work with a very long exposure here.
- Vineyards in Uhlbach and Rotenberg: terraced vineyards with a view over Stuttgart offer dramatic wide-angle long exposures with an ND1000, where passing clouds turn into soft streaks. More spots in our German-language Stuttgart photo locations guide.
Practical tips for long exposure with an ND filter
- Meter exposure before the filter: always determine the correct exposure time without the filter first, then screw on the filter and calculate the new time with the calculator.
- Tripod and remote release: from one second of exposure time onward, a stable tripod is essential. A remote release or the self-timer with a 2-second delay prevents camera shake from pressing the shutter.
- Autofocus before the filter: focus sharply before attaching the dark ND filter — many cameras struggle to find focus with strong ND filters attached. Then switch to manual focus.
- Use Live View and the histogram: with long exposures using an ND1000 or stronger, the image is barely visible through the viewfinder. Some camera models offer a boosted Live View display.
- Noise on long exposures: switch on long-exposure noise reduction — the camera takes a second "dark frame" of the same length and subtracts the sensor's inherent noise.
Want more practical tools? Check out our depth of field calculator — the ideal companion tool for planning your shots.
Frequently asked questions about the ND filter calculator
What is an ND filter and why do I need one?
An ND filter (gray filter) evenly darkens the incoming light without changing colors. You need it for long exposures in daylight (silky water, soft clouds), for a wide-open aperture in bright sun without overexposure, or for creative effects like making people disappear from busy public squares.
How do you calculate the new exposure time with an ND filter?
The formula is: New exposure time = original exposure time × ND factor. Example: 1/125 s × 64 (ND64) = 0.51 s ≈ half a second. Our calculator does this automatically — you only need to choose the base time and filter.
Which ND filter do I need for silky water?
For silky, flowing water you need at least 0.5–2 seconds of exposure time. In overcast light at ISO 100, an ND8 (3 stops) is often enough. In sunshine, an ND64 (6 stops) or ND1000 (10 stops) is recommended. Try different combinations in the calculator until the exposure time falls between 0.5 and 4 seconds.
Can I use two ND filters at the same time?
Yes. The factors multiply: ND8 + ND64 gives ND512 (9 stops). Pay attention to high-quality, thin filters (slim version) to avoid vignetting. The calculator supports stacking: just enable "Add second filter" and choose both filters.
Do I need to refocus after attaching the ND filter?
No — focus before attaching the filter, then switch to manual focus (MF). Strong ND filters like the ND1000 or ND64000 are so dark that autofocus can barely work at all. Focus, switch to MF, attach the filter, and shoot.
Hands-on in Stuttgart
Learn long exposure live — at night in the city.
Theory is good, practice is better. On the Night Photo Tour Stuttgart
we photograph long exposures, light trails and the Stuttgart skyline together —
with and without ND filters. You'll learn tripod technique, exposure planning
and composition on real subjects.
Or dive deeper into creative techniques like long exposure, light painting and
multiple exposure in the Experiments Workshop.