I know I asked this a month or two ago when I first got my RX1, but has anyone been able to get this to work? I'll set it in the flash drive mode I can only get it to work with the built-in flash. As far as I'm aware, rear-sync doesn't require any TTL communication, and is literally the camera firing the center pin at the end of the exposure. For some reason, it seems to ALWAYS fire at the beginning of the exposure unless I'm using the built-in flash. Am I missing something here? If you're able to get this working, could you tell me what flash you're using? Thanks so much everyone.