Very nice piece of equipment for 5D Mark II video adepts. The new Signh Ray Vari ND filter is a circular filter that blocks from 2 to 8 stops and that can be used gradually to smooth out light transitions. This way you can block the light when shooting outdoors to use lower ƒ stop for shallow depth of field. Or you can go inside and spin the filter to allow more light to match the ambient light for smooth transitions between two extreme conditions. A bit expensive, but a must if you are to shoot video with the Mark II on a regular basis.
Check it out here.