Mixed mode slave Speedlites and pre-2012 cameras
I’ve just found out that it is not possible to mix the modes of radio controlled slave flashes with pre-2012 cameras.
I love group mode that is available on the 2012 model year cameras, it lets you put some slave groups in manual, some in E-TTL II, some in external auto metering up to a total of five individual groups. You can then set the parameters of each group from the master ST-E3-RT or 600EX-RT.
What you cannot do is put a radio controlled slave Speedlite 600EX-RT in to manual mode by pressing and holding the mode button down on the flash. If the same flash is configured for pulsed light control then press the mode button for around 3 seconds and it will change the display to show individual slave.
Pseudo group mode with pulsed light control
With a slave set to individual slave it can be in manual or multi-flash mode. In essence it is possible to create a pseudo group mode with the pulsed light mode system. You could leave A group, B group and C group in E-TTL control from the master. Then have off-camera slaves in individual slave mode set to manual power levels for consistent light on backgrounds or subjects where the flash to subject distance doesn’t change. In this mode the individual slaves will simply respond to the “fire now” series of pulsed light commands from a master.
Solution: use the built-in pulsed light master flash on the EOS 7D
I was using an EOS 7D to take pictures of an EOS 5D Mark III and EOS 6D. Group mode wasn’t available and over radio control neither was the option to put one of the slaves in manual mode for consistent background illumination. I had to resort to pulsed light control using the Integrated Speedlite master (pop-up flash) on the EOS 7D and set the power level on the one manual slave directly, and let the other slave work in E-TTL controlled from the camera.
I could have put the ST-E3-RT in manual mode and have it manually control the power level of up to 3 Speedlite groups, but I was aiming to quickly light with E-TTL control for the subjects.
If you want to see what the combination of radio controlled Speedlite 600EX-RT and ST-E3-RT does provide, make sure to read my popular article: using the Speedlite 600EX-RT with pre-2012 cameras like the EOS 7D and EOS 5D Mark II.