What is a 10 stop filter? Thanks.
It's a fantastic shot and just shows what can be achieved in bad weather (especially if you are a photography genius!)
ND (neutral density) filters come in different strengths according to how much light they block out. A 10 ND is about as strong as it gets but give wonderfully long exposures, even in fairly bright weather. The slow shutter speeds then give the movement to the clouds and water.
Hope that helps. It's a fabululous image to illustrate the use of an ND!