Nick5 wrote in post #18136878
Canon ST -E3 RT will only communicate with the Canon 600 EX-RT's and 430 EXIII -RT.
And YN ST-E3-RT, and YN 600EX... 
I have been wondering if there is a 3rd party receiver that can trigger a the Studio flash.
I have been experimenting:
IF I set the ST-E3-RT to Linked Slave, and plug tha flash into the ST-E3-RT-s Jack "mount", and use the 600EX II as Linked Master on the camera, the studio flash will emit the flash, but there is a small delay,
that results in the camera taking the image, and the flash firing later.
If I set the camera to a longer exposure, say 0.5 sec, the flash is on the picture, if I have it at 1/125sec, the picture is dark.
So the camera is faster then the flash this way.
Yet a NON-ETTL reciever works fine.
So maybe there is a reciever, that "understands" the ST-E3-RT and can trigger a studio flash via the jack (cable).