This is not a FX/DX difference, it is a camera/housing difference. In fact, popular Canon FX cameras do not have pop-up flash, so you cannot use TTL with optical fiber unless you use a micro-strobe, which is not the easiest/cleanest way (and it won´t use the exact eTTL protocol).
Thanks for that, David. Sorry, I'm not familiar with Canon and was referring to moving from my Nikon DX to FX. Clarificaction appreciated!
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