If you are working in a huge studio or on a film set you may end up using a camera dolly. You mount a camera to a dolly and the operator and camera assistant usually ride on it while operating the camera. The dolly itself is similar to a small truck and is operated by a trained person called a dolly grip. A dolly can be used as a filming platform on just about any surface, however they are usually raised onto a small track like a railway track. The track is usually made of steel or aluminum with steel being the heavier and least expensive of the two. Most dollies have an hydraulic arm which can raise and lower the camera. There are two basic types of dollies: location dollies and studio dollies. Location versions are smaller and lighter and can be moved around. Studio dollies are bigger, more stable and stronger. Dollies are large and expensive items and are usually rented instead of bought and of course you can always build your own.