I have a Canon 5D3, program mode is selected, but when focus on subject I cannot adjust exposure + or -. with main dial I can vary Fstops, but when I attempt to vary EV with quick control an "L" appears and the exposure time is locked. I depend on being able to vary EV a lot as I am a existing light photographer. Does anyone have an idea on how to get rid of the "L" so I can vary EV's on the fly. thanks.