Here's the situation; I had a 600EX-RT in group C for a hair/kicker. It was aimed directly at the subject with the zoom at 135. It was too hot so I dialed the FEC on the STE3-RT to -3. It was still too hot. I went over to the flash and dialed -2 FEC into the speedlite. Now I had the light I wanted.
OK, today I did a test to determine if FEC on the 600EX is additive with FEC on the STE3.
The short answer is Yes.
I did three exposure tests;
First was zero FEC set on the STE3 and zero FEC set on the 600EX
Here is the result;
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This is a screen grab to show the highlight alert in Lightroom. It also appears that the power of the group C light was sufficient to add to the exposure on the front of the subject, bouncing off the diffusion fabric on the beauty dish.
Second was minus 3 FEC on the STE3 and zero FEC on the 600EX.
The result;
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There is just barely any highlight clipping indicated. But its still too hot for a hair light.
And it appears there is no apparent exposure influence on the face.
Finally, minus 3 FEC on the STE3 and minus 3 FEC on the 600EX.
The result;
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This looks the best. Maybe not quite enough hair light.
Worth knowing. I can see where this would be useful for lights in a reception venue as well. Provides some easy power adjustment while keeping the fill flash on camera in ETTL.
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