consider this. at f2.8, dof is shallow. if it is lowlight, and your body isnt able to handle, AF may always be off.
at f4, u have a better leeway due to the larger dof.
now, at f4, do you have enough light?
if not, what shld you use?
flash can work well if you are skilled enough. its fine to have the subject brighter than background by a stop or 2:think:
anyways... ttl for most brands get what u need. i suggest to rent a flash first. it can do wonders if used well.
if not for the flash i would never get these 2 shots. too dark.
the last shot is solely lighted by a flash bounced to the right of subject against the wall