Ok so I recently got a new little toy - a bigger softbox! Not one of those massive kinds used on stands, but one which is large enough to now cover over all the AF assit and other flash auto controls on the front of my 580EX2 - so its time for me to start learning more about manually controlling my flash power. However I have no idea where to start with this. I know that idealy one would use a ilghtmeter and take testshots to gague the power output needed for the flash - however my typical working conditions will not be studio based but outside based (and most likley hunting after bugs). So I need a way to start knowing how much to set the flash power output to so that I can ensure that I will get a good exposure.