Why my external flash failed to provide fill in flash?

Hi,


Last week, I attached my Speedlite 580EX II to my 50D and trying to take outdoor picture of my wife. The sun light is very bright, thus I want some fill in flash to remove shadow on the face. The photo become darker for the surrounding and my wife's face become yellowish.


I then remove the external flash and pop up the built in flash, it seems like the build in flash did better job. Fill in flash effect properly shown in the photo taken with built in flash.


When I attached the external flash, I did not enable Highspeed Sync, could this be the problem? I use Av and Tv, both with bad results. Lens is 18-200mm, f3.5-5.6, IS.


Appreciate any comments and guidance

Without seeing the images and the respective camera settings, I can't provide any specific help.


But it is doable with the 580 EX II, so something was wrong in some setting.