I have recently upgraded to a 580 exII from a broken 430. I am having some issues though and have some questions. I am using a gripped 40D. The other day I was trying to take pictures of one of my daughters toys against a white back drop. The camera kept under exposing (white back drop) so i did what i would normally do on my 430. On the camera i would tell the flash to use 1 stop more power. On the top of the 40D just click flash/iso button on top, and turn dial to one stop more power (three clicks)
The only thing was, the flash was still putting out the same power. Picture kept underexposing. It seemed no matter how high i turned the camera flash exposure compensation, the flash would still give same power. I had the camera on is 200 in M mode with (if I remember right) shutter of 1/100 and f/stop of f 5.0. The flash was in ETTL mode. I do not remember if i tried to use the settings on the flash to bump up flash power. What I did find that worked was put the flash in manual mode and set the flash power to 1/2 and 1/4 and 1/32 just trying to find right exposure. I was using a white balance backdrop to set exposer. (target with black Grey and white)
When in M mode the picture would expose right at I think 1/4 power. I know the 580 exII is much more advanced then the 430, it is self exposing? What sort of things do i need to know when using Camera Flash Exposure compensation?