This is the first I've heard of preflashing. I'm always looking for a bit more speed at those night football games. I usually just shoot HP5 at 3200 because Portra just didn't look that good above 1600 to me. I'll be trying this soon. So to make sure i have this correct, If I want to preflash 2 stops I meter through my diffusion material (tissue paper plastic, etc) at the ISO setting I'm going to shoot at, say 6400, then I just cut back the exposure 2 stops? So if my shutter speed was 1/500 though the tissue paper at 6400 I'd up it to 1/2000th, expose the film to the tissue paper then rewind and shoot the film normally at ISO 6400 and develop for ISO 1600 by pushing it 2 stops? Is there any advantage to doing this same method at rated speed. Would an ISO 400 film 2 stop pre-flashed at ISO 1600 developed at normal times be any better than just pushing 2 stops?