Catrake Force, North Yorkshire
So how do you do it? Well, neutral density filters are simply very dark sheets of material placed in front of the lens to reduce the amount of light entering the camera. Ideally these should be colour neutral, i.e. no colour shift is added to the original scene (hence the 'neutral' bit).
Up until now, ND filters were pretty much limited to 6 stops, but Lee Filters have now launched their 'Big Stopper' 10 stop ND filter. Judging by my example, it is very neutral and pretty much spot on a 10-stop reduction in light (although I have read that there may be some variation in strength between samples).
It is made of glass, and has a foam gasket around the outside edge of one side. The filter goes in the filter slot nearest the camera, with the gasket facing the camera. This prevents light leakage or reflections from light hitting the back of the filter.
As usual from Lee, a great bit of kit that does what it says on the tin.