If you have registered no camera data and visit the Macro or Micro page of the New Data dialog or the Edit Macro or Micro Data dialog, the Camera field will be presented as a text entry and you need to type a camera name by yourself.
By contrast, if you have registered camera data, the Camera field will appear as radio buttons representing the registered camera names. The default selection is the camera that has been selected or registered most recently. Just below the radio buttons is a text entry that holds the camera now selected. If you cannot find the camera name you are going to insert among the radio buttons, you can type whatever you want into the entry even if it has not been registered yet. Be sure that a text to be registered in the camera database is not the selected name of the radio buttons but the one in the text entry.