I found the problem to my 580 EX underexposure and I hope this helps you if you haven't fixed your problem yet. I recently brought my camera into Canon for sensor cleaning and after that came a consistent flash underexposure. Before taking the came...
I have the same problem with my 580 EX and have done similar tests with my flash. I have multiple flash units and the problem is only with my 580 EX. Tomorrow I am bringing the flash into the Canon Service Center in Irvine, CA. I will let you know...
