If I take a picture with an on-camera flash, or a single speedlight, my understanding is that the camera/flash pre-fire and then automatically select the approrpriate power level to properly expose the shot.
When you use two (or more) speedlights in a system (like CLS for instance), how do they automatically determine how much power each should use?
I can imagine plenty of cases where you would want one to be stronger than the other, would you have to set the power levels manually then?
I don't have any experience (yet) with off-camera flash, so I apologize if this is a stupid question, or if I have misunderstood how something like CLS is supposed to work.