[Jim K]

If you're trying to get the blown (white) b/g, this is my method and it works for me. You want your b/g to meter 2/3 to 1 full stop above your main. I start metering my b/g lights (2 x AB800s) one at a time for about f/11. Turn one on, then the other, but separately. After metering the b/g separately for balance, turn them both on and re-meter. It should now be about f/13 or so. Turn them off and go meter for your subject. I try for about f/8 for the main most of the time. If you're using a fill, go for about f/6.3 depending on your modeling.

When that's done, turn on everything and try a test shot while metering at your subject. At this point, I'm usually at f/9 or so. Set you camera to manual; 1/250 @ f/9 and shoot. It should be very close. These readings give you a full stop between the main and the b/g. You can fine-tune from there.

Good luck...