So I just spent half an hour trying to get the following photo. In the end it was taken with the little pop up flash of the GM1 as the only light source, tilted up and gobo'd with a little silver reflector into my DIY soft box. What I was actually trying to do was get the pop up flash to trigger my more powerful optical slaves (YN560-III, Nissin i40). I tried both manual slave (S1/SF) and TTL suppression slave (S2/SD) on both flashes, to no avail. Manual slave would trigger too early, and TTL suppression slave basically wouldn't trigger at all. I got it to go off once or twice with the slave stuck at some arbitrary distance from the GM1, but it wouldn't really work properly. Is there any way of getting the GM1 to trigger optical slaves or at the very least be able to turn off TTL flash?