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?
ETTL will fire a test flash and some coded flashes in order to set the flash exposure, but you can set the internal flash to not flash during the actual exposure, even though it fires to communicate with the slaves, it will not contribute to the exposure. Read the manual very carefully.
".. it fires to communicate with the slaves..."
Think about it for a minute. If there is no exploratory flash how will the camera know to set the exposure. Unless you go to full manual, the camera has to know what to do. Make sense?
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