How and when to use ND filters (and what the numbers mean)

When and how to use ND filters

Have you ever wondered how pro photographers capture movement in their landscape shots to produce soft, blurry clouds and misty waterfalls? Are your long exposures just not delivering the same effect? Chances are that those pro images have been shot using a neutral density filter. These dark filters are designed to reduce the amount of light reaching the sensor in order to increase exposure times, without affecting the colour of the image. But how do you know when to use ND filters?