Seems like you need another field in each table in order to set up a relationship between them:
Staff::StaffID = Photographer Jobs::StaffID
Staff::StaffID would be an auto entered serial number.
What you describe is called a conditional value list. Here are some links, Option 1 in the first link, is a limited form of a conditional value list you may want to use for this specific issue.
Forum Tutorial: Custom Value List?
Knowledgebase article: http://help.filemaker.com/app/answers/detail/a_id/5833/kw/conditional%20value%20list