Assistant Cameramen are of two categories- the Second Camera Assistants and the First Camera Assistant. The Second Camera Assistants are responsible for maintaining the camera and the updating the tape stock. They charge the batteries and keep all the other equipment ready to ensure that there is no time lag. They make sure that all the arrangements are made so that in case the Director of Photography has sudden demands. They also maintain a camera log and have a complete record of the shots being shot in which role and so on.
Meanwhile, the First Camera Assistants, also known as the Focus Pullers, support the DoP more closely. They calculate the appropriate focus for each shot and the other camera variables as well. For every shot (takes and retakes) they control and maintain the lenses and the focus. They also keep a check on the camera kit. Camera assistants maintain and label all the camera accessories.