Sadly, if you need to work

Sadly, if you need to work wide open, you're stuck. I've never seen any proper camera with this facility. It's actually quite a good one, but I'm not sure how they'd do it, because it's an optical function – the actually iris doesn't change on most, but the aperture difference is an effective one, rather than a mechanical one – so there's no feeedback for the camera to base the gain on, if it just gets dim, auto could kick in at the wrong moment – when something bright crossed the frame. I like the idea, but have never seen it implemented as a feature.