How does wireless ETTL work?

Started Jun 18, 2014 | Discussions thread
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RER220
RER220 Junior Member • Posts: 34
How does wireless ETTL work?

I was thinking of picking up the speedlite 600ex-rt and the wireless remote as well. I generally understand how ettl works when on top of the camera, but how does it how much light to  output if it doesn't know how far away it is from the subject? How would the camera know if the flash is 1 foot vs 5 ft away cause that would require different flash out puts.

 RER220's gear list:RER220's gear list
Fujifilm X100S Sony Alpha 7 Canon EF 50mm f/2.5 Macro Sony FE 35mm F2.8 Sony FE 55mm F1.8
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