ND8 means 1/8 of light is passing through. This equals 3 stops, not enough if you look into the table at catchlights' link. ND400 will cut about 10 stops, enough to get several seconds exposure time in daylight with f/11 and ISO 100.
More to read about ND: http://en.wikipedia.org/wiki/Neutral_density_filter
Great info..guess i need a ND400 then..are there ND 200 or 300? I think it cost in the region of $100? :sweat: