« on: March 21, 2011, 01:00:43 PM »
In fill mode the camera will meter primarily on available light, and use the flash for fill. (still put FEC to -1)
With my 5DII and a Speedlite, my decision is not whether to apply a negative FEC, but how much negative FEC to apply...usually anywhere from 2/3 to 1.5 stops.
I use -1 as my starting point, and that's where it stays 90% of the time. The only time I've really had to change it is if I'm bouncing off a colored wall, and it's metering funny; or if I need to overpower a mixed light source.