A camera assistant is a member of the production team who works in the camera department, assisting the director of photography and camera operator.
In modern Doctor Who, the credit "camera assistant" is approximately equivalent to "2nd assistant camera" or "clapper loader", with the 1st assistant termed the focus puller. Their main responsibilities are operating the clapperboard at the beginning of each take, marking the actors as necessary, and maintaining all records and paperwork for the camera department. On film shoots, they would also be responsible for loading film stock.