OK. I got a brand new Nikon SB-80dx flash unit for my anniversery. It is VERY nice and has some interesting capabilities, including very short flash durations and a repeating strobe function. The repeating strobe function looks like something that I would like to play with. The general theory I know. Long shutter speed (probably Bulb) and adjust the exposure for the strobe subject. How, however, do you keep from overexposing the background? Is the only way to use a dark background? This is something I'd like to play with but need some exposure advice/help.