Lesson 10 Canon Transmitter ST-E3=RT and 600EX-RT Flash

Bruce Dorn's Introduction to Canon's Speedlite's system click here


Quick Guide to Speedlite Transmitter ST-E3-RT Setup click here

There is a way to adjust the Speedlite setting on the 5DMIII.  Check out where to find Flash Function Settings in the 2 pages from the camera manual.  You might find it easier to make adjustments: