Lee filters has launched this month (March 2010) their own version of the 10 stop filter. These types of filters are all the rage at the moment. The above image is shot with the G617 on Velvia slide film during the middle of the day with the B&W 10 stop ND filter. The lee filter is 100 x 100mm, made of glass and will slip into your standard lee filter holder.
My first though with a set up like this is “will it be light tight”. The shutter speeds these filters give you on digital and most definitely on film demand that it needs to be light tight. The Lee 10 stop is said to have on one side a thin foam gasket to make it light tight when inserted into the closest slot to the lens. Lee also state that the filter has been designed with an infrared layer to remove that warm cast you get with other 10 stop filters like the B&W. If anything they say you might get a slight blue cast.
One advantage the filter has is that you can use your other ND grads with the holder if you need to control the sky (my kit is set up with 2 slots). I know you can screw your lee adapter ring into the front of the B&W filter but you are risking vignetting with that kind of set up especially with wide angle lenses.
The price is about 94 pound ($156 Aust). If your interested here is a link for more info on the Lee site.
I have just ordered one from the UK and when it arrives I will put it through it’s paces and let you all know.