Is there a setting on the Canon 5D Mk III where I can override Av (aperture priority) mode so it will lock on the aperture setting regardless of whether the camera thinks a 30 second exposure isn't long enough?
For example, I like to shoot lightning at night and a good aperture setting is f/7.1 because it is very bright so I need to keep it there. The camera will max out the exposure at 30 seconds, but what's happening is the camera is automatically changing the aperture to f/4.0 because it thinks there isn't enough light. But when a lightning strike hits, it gets over exposed at f/4.0. I need to keep it at f/7.1 … is this possible?