The role of the First Assistant Camera (1st Assistant Camera, 1st AC - and previously know as the Focus Puller) is one of the most skilled jobs on a film crew.
1st ACs are responsible for focusing and refocusing the camera lens as Actors move within the frame of each shot. They do not look though the lens to do this but 'pull focus' according to a set of complex marks placed on the set, floor, props, etc., during rehearsal.
As it is impossible to see whether the focus is sharp until the rushes (raw footage) are screened, 1st ACs rely on experience and instinct for each focal adjustment. Because re-shooting scenes is expensive and actors may be unable to recreate their best take, 1st ACs must be extremely reliable and good at their work and should be able to cope effectively in stressful situations.
1st ACs are also responsible for camera equipment such as lenses, filters and matt boxes and for assembling the camera and its accessories for different shots.
They arrive on set or in the studio before the Director, Director of Photography and Camera Operator and ensure that the camera and all required lenses are prepared for the day's shoot. If the Director or DoP wants to try out a specific lens, the 1st AC assembles the camera so that they can look through the eyepiece to assess the shot.
At the end of each shooting day, 1st ACs clean the equipment and pack it up in preparation for the next day. If there is a problem with the rushes (such as a scratch on the film), they liaise with the film lab to put right any faults with the camera or stock.
1st ACs are usually asked for by the Director of Photography or the Camera Operator and work on a freelance basis. Hours are long and the work can be physically demanding.