I'd leave the ISO alone...........either increase your shutter speed or open up your aperture. I've had my shutter speed at 30" at times. I am assuming there is a tripod;-)
steve272 wrote:
This was my best result using much the same process. Homemade variable nd filter (flip one polarizer and stacked 2 polarizers) with a 4 ND filter. Shot at 8 sec f27 100 ISO.
Myself, I'm buying a ND10 filter before I try this again.
Good luck!