I have a Vivitar 2000 flash that I picked up months ago, but I'm still struggling with how to use it. The flash has a three mode selector switch, Automatic f/5.6, Manual, and Automatic f/2.8. If I were to use it on my EM or FM-10, what modes should I use? I understand the concept with one problem, how do I know what shutter speed to use? I've been told to set it to the camera's max synch speed, but if every camera has a different speed, how are proper exposures ensured with different cameras? On my FM-10 the synch speed is 1/125 and on my EM is 1/90. Won't that result in a brigher (and possibly overexposed) image with the EM? Thanks for all the help, guys!