How to Use an ND filter
If you want to achieve the sort of milky seas and scudding clouds found in many pro coastal shots you will need to take very long exposures. Your choices then are to shoot before dawn or after dusk, or to make use of neutral density filters. These filters come in stop ratings, which give the exposure compensation you will be able to make when they are placed in front of your lens. A 10-stop filter will turn a ‘normal’ exposure of 1/60sec into a 16-second exposure. Shutter speeds of several minutes can be achieved by stacking multiple filters on the lens.
Calculate your exposure
ND filters are rated in stops and you can download charts that will show you the new exposure time. If you exceed your camera’s maximum shutter speed use the ‘bulb’ setting.
Compose your shot
Set up your shot without the filter in place and take a regular meter reading of the scene. Once you’re happy, attach your ND filter(s) to the lens.
Take your shot
To avoid camera shake with long exposures, use the self-timer or a remote trigger release. When making very long exposures it is good practice to cover the eyepiece in order to avoid light leaks.