There are situations in which 1/1000 sec and 100 iso film won't give you the the effect you try to achieve. When I take pictures of streams and lakes I want shutter times from at least 1/4 sec, going down to sometimes half a minute and more. Stopping down helps of course, but a ND filter serves a very good purpose also. I always carry two of them: a 3 stops one and a 10 stops one. The 3 stops I also use when I want to take pictures wide open and there is more light then the fastest shutter speed can take, for instance when using the 360 tele-xenar in it's Compur3.
Originally Posted by jp498