Why do I get under exposure when shooting straight on with a sto-fen on a 580EX II or 430EX II in E-TTL mounted on a 1Dmk3 or 7D in P, Av and Tv? Note that if I use FEL the exposure is set correctly.


This issue only occurs shooting straight on. As soon as I bounce the flash head in any direction then the exposure is fine.


I thought using E-TTL that I shouldn't need to worry about this?? Any insight and help you can give as to why this is occurring (and how to fix the issue while still shooting straight on without FEC ) is greatly appreciated.


Thanks,
A