Screw on ND filter for Canon L lenses?

[Rodreguez]

I always see pictres by people like David Noton and Guy Edwardes with movement in the water made to look smokey with long exposures, yet are done in broad daylight. This must surely involve a very heavy ND filter? I bumped into a guy once who had screw on one for his 1DS MK2 which I thionk he said he used for the same thing. I seem to rememebr him saying it was 8 stopd or something.

So, can anyone tell me what it is exactly that I need, and where I can get it? I have the 17-40 L lense, and I want to use this filter with my polariser. Is it a screw on one I need, and can it be used with my screw on polariser?

Thanks

Rod

[sfaust]

It is a standard filter, and you can get them at any professional photography supplier. If you can't find one locally, try B&H (B&H ND Filters) (http://www.bhphotovideo.com/bnh/controller/home?A=search&Q=&b=109&a=27_307&a=71_524&mnp=0.0&mxp=0.0&cmpsrch=&cltp=&clsgr=&shs=&ci=114&ac=&Submit.x=16&Submit.y=4&Submit=Go). Just match the filter size of your lens, and pickup a 2x, 4x, and 6x. You can then stack them to as needed to get the effect you are after. If you do stack them, be careful and check for vignetting.

[PhotosGuy]

A CP will give you 2X. Two will give you a LOT! ;)