Camera range too wide

I'm using an iMac for Zoom calls and the default setting is quite a wide shot but I can't find a setting to narrow what the camera displays. Does anyone know if that is adjustable and where it can be changed?

I've looked in the video settings within Zoom but could find nothing in there. It states it's using FaceTime HD Camera (Built In) and doesn't give any other options, so I'm getting the impression there's nothing I can do to narrow the field it shows?