There are a couple of view mods in the Download Centre that do that kind of thing.
The field of view is defined individually for each camera view that each bus has. To customise them for your own liking, you'll need to open up the *.bus file for the bus you want to customise and edit the [add_camera_driver] entries for the cameras you want to edit. Hopefully they're labelled with what they are. I've documented the [add_camera_driver] keyword here.