[obsoquasi]

Hi you two and thanks a lot for your suggestions as to what might cause the problem. I seriously suspect that there is a problem with the meter. I did some further tests comparing the results of an ambient reading and a mixed reading. The result: ambient reading are fine, mixed will often overexpose, especially if the ratio flash:ambient is to 100%. I'd love to see what the results would be if a sync cord is attached, but my 580 EX II's aren't sync-cord-compatible without some serious tinkering. In any case, thanks again for your thoughts, it was reassuring to hear I was basically on the right track.