Actually tracing paper is a better light diffuser in most situations, but if the results are good keep experimenting.... Anyways, depending on the ambient light, your shutter shouldn't have too much affect on freezing your subject if you shoot with a flash. Your flash is what strobes your subject and freezes it and the ambient light will only add streaks depending on how much ambient light is given off. If you see a streak or slight blur from the "Ghost" of the ambient light, you can eliminate it by increasing the speed of the shutter, but that is something different since the main subject should be frozen by the flash, not the shutter;especially since most SLRs will only synch 1/250 sec or slower. In a dark room, you can shoot at 1/2 second with flash and it will freeze a moving object. The faster the strobe/flash the better the results, but it is very subtle. If you are using an SLR with hotshoe flash check to see if you can point the flash up and if it has a white reflector card and diffuser slide out like the Nikon SB-28 or SB-800. Most flashes can't adjust for close up or at the extreme of macro; just like your lense, that's why they have a diffuser built in , but often the plastic diffuser isn't enough so you need to use a secondary one, a bounce, a white diffuser like your white paper or soft dome. When using a flash, most 35mm SLR's can only synch up at 1/250 of sec or slower, so it won't freeze if moving fast without the use of a flash. The idea is to allow the flash to freeze the subject and use your shutter to let ambient light in on the items not lit by the strobe, but it is a balancing game since the ambient lit objects will blur if the camera is moving and not on tripod.