Originally posted by normhead Is that like the one where the camera will focus, but it's so dark you can't see where the camera is pointed through the viewfinder, so you don't know what you're focusing on?
Just about. The somewhat silly aspect of impressive tech like -4 EV autofocus on some cameras is that the metering often (eg on the GM5) only goes down to -EV 0. So you will have a focussed shot, but the camera probably won't be able to expose the scene properly. Such cameras will need good dynamic range, because you'll probably be doing a lot of shadow boosting in post processing. It's probably useful though for keeping the AF working with dark lenses.
FWIW, the K-3 (-3 EV AF, -3 EV metering) and A7S (-4 EV AF, -3 EV metering) are the only cameras that properly balance deep low-light AF and metering.