I realize the technique I’m about to describe is a hack and very much a huge edge case. The reasons to drive multiple flashes in a half RF half optical setup like I’m about to describe is becoming vanishingly small.
The first time I tried wireless flash triggers, they were unreliable and that was being kind. Whether it was RF noise from the flash or some strange sync issue, they were so unreliable for me it wasn’t worth trying to use them. It didn’t take me long to get a pair of LPA Design’s PocketWizard Plus 2s. When I finally got around to adding a second flash, the radio trigger market was poised to go TTL; Radio Popper had their first TTL system out already and Pocket Wizard wasn’t far behind. Instead of springing for another Plus 2, I elected to save the money and wait for Pocket Wizard’s TTL system whenever that came out. It was out of that necessity and experimentation that I figured out how to get working completely wireless two light setup with only 1 pair of radio triggers.
- A Canon Speedlite capable of being used as a ETTL Master flash (i.e. 550Ex, 580Ex, 580Ex II, ST-E2, etc.)
- 1 or more Speedlites that can be slaved under Canon’s ETTL wireless system.
- A pair of radio triggers (or a PC Cord)
- A basic PC-cord to hot-shoe adapter
Mount the master flash in the PC-cord hot shoe adapter and connect the adapter to the RF receiver (or the camera via a long PC cable). Set the master flash to wireless master mode.
Set the remote flashes to slave mode the same as you would if you were using an on camera master. Place them where you want them.
What Works, What Doesn’t, and What are the Limitations
First off, TTL does not work. This is not a TTL setup.
Remote manual power control and stroboscopic mode do work, so long as the master supports them. A 580Ex II will drive any other slave-able Canon flash in stroboscopic mode.
The largest limitation is in sync speed. I found on my EOS 40D that I was limited to about 1/160th instead of 1/250th. Using the master to control the power of the remotes hits the sync speed even harder. The best sync speed in this configuration is reached when the master flash is set to group a, with no ratios and the slaves control their own power levels.
With the availability of more reliable cheap wireless triggers, this technique isn’t very useful any more. It’s made even more redundant by the availability of very good RF TTL triggers like Pocket Wizards’s ControlTL system and Radio Popper’s X system. In short, it’s probably not worth bothering with this unless you’re in a pinch and don’t have any other backups available. I certainly don’t use this any more.