I'm much more experienced in still photography than I am at videography, but this weekend I'm shooting a music video for a band that I have done some work for in the past. Our goal for one of the sections is to use my 580exII flash in stroboscopic mode to fire off 4 flashes per second, and we want to record that on video. I tested it out this morning, but there is a rolling shutter effect when I view the footage. Each time the flash pops, only half the frame or less is lit. I want to be able to see the whole frame lit for each flash pop. Does anybody have any helpful tips for me?