I am trying to find a way to keep the built-in flash from firing when using an external (off the camera) flash. The flash is E-TTL compatible, and I'm able to communicate with it i.e. change the settings even when it is not attached.
On page 219 in the 800D instruction manual, there is a note saying that if I disable the built-in flash, it will still fire to control the slaves. How is this possible? If I disable the built-in, no flash occurs at all. Yes it does emit low level flashes to perform AF-assist, but no flash from the external when shooting. And in this mode, no flash control at all.
Are these truly features of an E-TTL II flash? Or should I expect an E-TTL compatible flash to work?
Further, I don't understand how the built-in can be disabled. Is this through the firing group and specify external only?