Quote Originally Posted by Mark Elberson View Post
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David Hobby over at www.strobist.com estimates the 580EX to be at around 60 watt seconds. The reason why the 580 has a guide number of 190 is because it's measured at its tightest zoom of 105mm. The standard reflector on an AlienBee has a spread of about 80 degrees which is probably much closer to 24mm of zoom on a 580. The fastest duration on an Einstein though is 1/13,000 which can easily be beat by a 580. 1/13,000 isn't too shabby though :-)
As I said before, Thanks Mark. Also, after trying to learn some more about how to compare light output of different units, I ran across this article on the PCB website. It was very informative, but still left me wondering how a newby is to determine the "best tool for the job" when the various power ratings and other specs are mostly marketing hype. Well, word of mouth and satisfaction of current users usually leads me in a good direction, so I will stick to that for the moment; at least until someone mandates a rationale standard that must be used by all manufacturers. Even so, This was a good read for anyone that uses or is planning to use monolights or powerpack lights.