How do I photograph moving water so it looks silky?

Silky water is not a filter or an editing effect. It is a record of everything the water did during the exposure, and the only variable that matters is how long you left the shutter open.

What you'll need

• A tripod
• A neutral density filter for daylight
• A remote release or the self-timer

Step by step

1. Choose the exposure length by the effect you want.Around a quarter of a second keeps individual strands of water visible and looks energetic. One to two seconds smooths it into flowing ribbons. Five seconds and beyond turns a waterfall into fog and the sea into mist. Faster-moving water needs a shorter exposure for the same effect.
2. Fit the camera to a tripod properly.Legs spread fully, feet on solid ground rather than on a springy bank, centre column down. On a beach, push the feet into the sand and be aware that a wave washing round them will settle them mid-exposure.
3. Set the base ISO and a middling aperture.ISO 100 and f/8 to f/11. Going beyond f/16 to extend the exposure costs sharpness to diffraction — use a filter instead.
4. Work out how much filter you need.Meter normally, then count the stops between that shutter speed and the one you want. Each doubling is a stop. A three-stop filter turns 1/8 into about half a second; a six-stop turns it into four seconds; a ten-stop takes you to half a minute.
5. Focus and compose before fitting a dark filter.A six- or ten-stop filter makes the viewfinder nearly black and autofocus will fail. Compose, focus, then switch to manual focus so it cannot re-hunt, then fit the filter.
6. Trigger without touching the camera.Two-second self-timer or a remote release. Pressing the shutter with a finger shakes the camera for the first fraction of the exposure and softens the whole frame.
7. Watch the rest of the frame.Long exposures also blur foliage in wind, cloud across the sky and anyone who walks through. Sometimes that is the picture; often a moving branch in an otherwise still scene looks like a mistake.
8. Take several and compare.Water is different in every exposure. Take five at the same setting and one will have a better arrangement of flow than the others. Also bracket the exposure length — the difference between one and four seconds is a different photograph.
9. Check for reciprocity and noise on very long frames.Exposures beyond about thirty seconds need bulb mode and can produce visible sensor noise as the sensor warms. Long-exposure noise reduction helps and doubles the time each frame takes.

Tips

• Overcast days and the edges of the day are the easiest, because the light is already low enough that you need less filtration.
• A polariser costs about two stops and also removes reflections off wet rocks, so it often does two jobs at once for gentler effects.
• Sea spray on a filter ruins every frame. Check and wipe the glass between shots when you are near surf.

Common mistakes

• Trying it handheld — Any exposure long enough to blur water is far too long to hand-hold. The result is blurred water and blurred rocks, which is just a blurred photograph.
• Using a very long exposure on everything — Thirty seconds turns every waterfall into a shapeless white smear. Fast-moving water usually looks better at under a second, where you can still see it moving.

If it doesn't work

Questions people ask