watash1965,
A lot is going to depend on the time of day you are taking your photograph, and how long you want to expose your shot for, to get the blur you want.
A quick way to determine how long to set your shutter speed is to meter or take a normally exposed shot, take your shutter spedc and multiply it by 64.
Let's say it's dusk, and when you expose for your shot the shutter speed comes in at 1/30. When you add your 6 stop filter, you would set your shutter speed at 1/30 X 64, or 2 seconds. If the normally exposed shot was 1/10, when you add your filter, it would be 1/10 X 64, or 6 seconds.
Steve Thomas
