I've had a 580Ex for about 4 or 5 years. I picked up a used 580EX this week. Today I wanted to see how well matched they are at an given power setting. So I set them both to manual and to the same power levels. I set all the custom functions and the zoom head the same, too. I set the camera to manual exposure, then alternated taking photos of a gray card with each flash. It appeared that the used flash I just got is 1 stop less powerful than my original flash with all setting gas the same.
Is this an indictation that the flash is damaged? Maybe it was overheated at some point?
Thanks in advance.
