Weird operation with NEW 550EX and 100-400mm L but not other

[JCalvert]

My 550EX flash somehow does not like the 100-400mm L lens, it fires very randomly. Sometimes with enough juice, sometimes only about half enough and sometimes the pictures are BLACK.

But with the 17-40mm L and 28-135mm , the 550EX seems to fire 98% of the time.

Has anyone else experienced this? Have I adjusted one of the several hundred settings on the 10D or the flash improperly?

Thanks
jc
:?

[Longwatcher]

Cannot remember if I had same problem or not, but I found that when using 550EX with 70-200/2.8L on 10D, I need to use the 550EX set to manual and zoomed to longest focal length. Works almost everytime there.

[CyberDyneSystems]

Disable "auto reduction of fill flash" or some such thing via a custom function...


...I think.. who am I to talk,. I don't even have a falsh unit. :)