Help please,

I was taking a portrait in bright daylight, and wanted to use fill in flash for highlight in eyes and on lips. Canon 5D, 580 flash. Canon f2,8 70-200L is. Aperture priority, ISO100.

Aperture selected, f2,8 for shallow Dof F, gave 1/4000 shutter speed.

When flash used, camera changed aperture to f13 and 1/200 shutter speed.

I know why it did this (for flash sync), but is there anyway around this. i.e. maintain shallow D of F, but still use flash in bright conditions?
Thanks in anticipation.

Your 580 EX has what's known as FP mode (Focal Plane), a.k.a.. HSS (High Speed Sync) that lets you exceed the camera's x-sync speed. It works by pulsing the light as the shutter curtains move across, so it will impact your flash range and recycle times.

You'll have to look for it in your flash manual. But, it's probably just a quick mode change to FP mode on the flash.

Hi linigiv,
try putting your flash to manual and dial into the flash minus 1.7
Try it out it should work.
Cheers Finzie