Have seen a number of queries on photo forums about the use of flash triggers with the E-M1. On one forum, a respondent went through a modification needed to make them work, which included opening the triggers, cutting wires, and re-soldering. Well, I can tell you for certain that the two sets of Yongnuo flash triggers I have work well, without any mods. They are the RF-603C II (for Canon), and RF-603N II (for Nikon). In theory, the only difference is supposed to be a supplied cable for, I believe, shutter release, but I have never used the cable. There is a subtle difference in the pin layout on the bottom of the triggers, but both versions still trigger an external flash with the E-M1, 100% of the time, with no issues whatsoever . Hope this helps someone.