So at wedding receptions I use the 5D with a 580 mounted, and I also use a Cybersync trigger velcro'd to the side with a mini-sync cord going into the sync port of the 5D. With the cybersync, I like to trigger a couple of 580's popping on the dance floor.
However I've encountered a problem. The off camera flashes don't seem to pop every time when I have the on camera flash turned on. When I turn off my flash, the OCF's pop every time. Then sometimes the on camera flash won't fire, but the OCF's will.
Last week I was using ETTL on camera, and popping the OCF's just fine, every time. This week they were troublesome.
Can anyone explain what's going on here, or what I can do to fix this? PCB says you have to shoot with the on camera flash set to Manual, but I swear I was using ETTL last week.
Here is a picture of the setup in case my explanation wasn't clear. It does the same on the 5D and 5DII. Quite vexing.