Hi everyone. I have been practicing with the AV mode on my EOS 80D. I had it set at F3.2. The ISO was 640, shutter speed was 1/500 for a sequence of shots, then went to 1/1600 and the pics were all clear. However the shutter speed suddenly jumps up to 1/8000 plunging those pics into darkness! Can anyone help with why that happened and how I avoid it in future? I was shooting runners, outside if that helps!