Dolly Grip
1. In cinematography, the dolly grip dedicated technician trained to operate the camera dolly. The individual places, levels, and moves the dolly track, then pushes and pulls the dolly and usually a camera operator and camera assistant as riders. If the dolly has a moveable vertical axis, such as a hydraulic arm, then the dolly grip also operates the “boom”. If both axis are used simultaneously, this type of dolly shot is known as a compound move.
A dolly grip must work closely with the camera crew to perfect these complex movements (cinematic techniques) during rehearsals. Focusing the lens is critical to capturing a sharp image, so a dolly grip must hit his/her marks in concert with a camera assistant who pulls focus. It is a skill that experience can hone to a point, but the best dolly grips are known for their “touch” and that makes them highly sought-after talents. Despite this expertise, these key members of the filmmaking community have on occasion been dubbed with the derogatory term, “dolly jockey”.
Source: Wikipedia