Yes it is compatible. But compatibility depends on the camera body the ST-E3-RT is mounted to. But all R series cameras are fully compatible with all of its features. The EL-10 needs to have wireless turned on and set to the same channel as the ST-E3-RT. This can be accomplished on the ST-E3-RT or through the speedlite control menu in the camera. The ST-E3-RT comes in 3 different versions those are version 1, 2 & 3.
-Demetrius
Bodies: EOS 40D & EOS 5D Mark IV
Lenses: EF Holy Trinity, EF 50mm F/1.8 STM, EF 70-210mm F/4 & EF 85mm F/1.8 USM
Speedlites: 420EX, 470EX-AI, 550EX & 600EX II-RT
