Just had a quick look in the manual (easier to find than I expected) and the answer seems to be on page 119. In the menu system go to flash control > built-in flash func. settings > wireless func. - you need to then select external flash only (I think it is the third option with a symbol that looks like a flash gun). That should leave it firing the 580 with no light coming from the onboard flash. Also make sure that you set the flash mode to manual, as if you leave it in ETTL II I think it can override the manual settings on the flashgun.
|