Ok guys, just for you. I set up a controlled experiment in my bonus room. I placed a light stand in one corner of the room, and my camera on a tripod on the other. On top of the camera I had my PCB Cyber Commander. The CC features a light meter--handy for measuring relative exposure differences for our little test. On the light stand I placed a monolight firing into an umbrella. The monolight was set to 394 w/s (because the CC wouldn't let me choose 400 on the nose). I used an umbrella swivel to place the umbrella in exactly the same place as it was with the monolight. I tested out a few shoe-mount flashes with the CC set at 100 ISO and the results were...


Ultrazap 1600 set to 394 w/s f/8.0'2


580EX full power, 24mm zoom f/2.8'9


YN560 full power, widest zoom f/2.0'2


285HV full power, widest zoom f/2.8'2





So, relatively speaking, the monolight at 400 w/s equals a little more than (4) 580EXs at full power.