Hi,
However, if “specify focus” is left off, will the center of interest affect DOF as well?
Yes, camera focus will be taken from the camera aim (Specify focus Off). If you switch it to On, you will be able to control the camera focus field and camera target separately.
get confused as there are now 4 potential places to enter a value for focus/exposure distance from the camera
Yes, there are a lot of options and parameters that allows the user to control the camera, but most of them are overridden by the V-Ray Physical camera.