Camera's Up

There are other ways to announce to the crew that rolling camera is about to begin, however the phrase "camera is up" is usually a specific indication that the camera is currently physically resting on the shoulder of a camera operator, in the operators hands, mounted to a Stedicam rig or some other precarious mounting of the camera. Cameras and rigs are normally rather heavy and when "camera is up" is announced on the set, it's a call of respect to shift all attention to the camera operator in order to shoot the scene before wearing out the camera operator with further waiting.