Long Exposure Photography Timer
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Common uses for a long exposure photography timer
- ND filter long exposures
- Converting metered time to filtered time
- Water and cloud movement
- Bulb mode timing
A neutral density filter reduces the light reaching the sensor by a stated number of stops, letting you use a much longer shutter speed in bright conditions. The conversion is straightforward doubling: each stop doubles the exposure time, so a 10-stop filter multiplies the metered time by 1024.
Two minutes is a common long exposure for water and cloud movement — long enough to render moving water as smooth and clouds as streaks, short enough that you are not standing in one place for a quarter of an hour. Beyond about four minutes the visual difference diminishes while the waiting does not.
Do the conversion by doubling
Meter without the filter, then double the time once per stop. A metered 1/125 with a 10-stop filter doubles ten times: 1/60, 1/30, 1/15, 1/8, 1/4, 1/2, 1, 2, 4, 8 seconds. It is faster in the head than any app once the habit is there.
Metering through a strong ND is unreliable because the camera's meter struggles at that light level, which is why the meter-first-then-convert order matters. Compose and focus before fitting the filter too, since autofocus generally fails through a 10-stop.
Reciprocity failure applies to film, not digital
Film loses sensitivity at long exposures in a non-linear way, so a calculated two-minute exposure may need four or more. The correction differs per film stock and the manufacturer publishes it, which is the figure to use rather than a general rule.
Digital sensors do not have this behaviour. They have their own long-exposure problem — thermal noise — which is what long exposure noise reduction addresses, at the cost of doubling the time you spend per frame.
Light leaks are the other long exposure failure
Over two minutes, light entering through the viewfinder on a DSLR can fog the image visibly. Covering the eyepiece — many cameras ship with a cover on the strap for exactly this — takes a second and prevents a wasted frame.
A sturdy tripod and a remote release or self-timer matter for the same reason. At these exposure lengths, the difference between a sharp frame and a soft one is often the photographer touching the camera.
Multiply the metered shutter speed by the factor. Each stop doubles the exposure time.
| Filter | Stops | Multiply by | 1/125 becomes | 1/15 becomes |
|---|---|---|---|---|
| ND2 | 1 | 2× | 1/60 | 1/8 |
| ND8 | 3 | 8× | 1/15 | 0.5 s |
| ND64 | 6 | 64× | 0.5 s | 4 s |
| ND400 | ~9 | 512× | 4 s | 34 s |
| ND1000 | 10 | 1024× | 8 s | 68 s |
| ND1000 + ND8 | 13 | 8192× | 64 s | 9 min |
| ND100000 | ~16.5 | ~93000× | 12 min | — |
- Meter and focus before fitting the filter — autofocus and metering both fail through a 10-stop.
- Reciprocity failure applies to film only; use the manufacturer's correction for your stock. Cover the viewfinder on a DSLR.
Source: Stop-to-time conversions are direct arithmetic — each stop doubles exposure time
Sources
- Stop-to-time conversions are direct arithmetic — each stop doubles exposure time , TheTimerLab — accessed 2026-07-28