If you have the ST-E3 out of a hotshoe, it is possible to trigger all Group flashes in Manual mode with pressing the Test Flash button (illuminated red button). All radio linked slave flashes will fire correctly according to their group settings.
So what?
Well, if you instead trigger the ST-E3 through its hotshoe, via an external trigger source (i.e. not sitting in the hotshoe of a camera) the slaves will NOT fire.
I do a lot of high speed flash work, using open flash technique with auxiliary external high speed shutters. I use the high speed shutter to provide the synch signal to my flashes (the camera is in Bulb mode). Sending this signal to the hotshoe of the ST-E3 produces nothing.
I corresponded with Chuck Westfall about this issue, and he confirmed the ST-E3 needs the presence of a camera to fire the radio connected slaves. When I mentioned the Flash Test button happily fires all the radio connected slaves he was surprised. I then suggested I butcher an ST-E3 to externalise the Flash Test button contacts, so I could use that as a trigger input. He mentioned the voided warranty etc, but was interested in the result.
It worked.
Hopefully the next-gen ST-E3 will have focus assist, an external trigger input and Second Curtain Synch. None of these features even approach rocket science.
Roy.
