What is a dovetail plate?
A dovetail plate, also called a sliding plate, is the basis of most camera support systems used in feature film productions. It is a metal (usually aluminium) plate with a specific, finely machined profile upon which a variety of accessories can be attached or supported. Mainly, the dovetail plate serves as a base for the camera, which is attached to it using a dovetail clamp or a bridge plate. The key function of the dovetail plate is to allow the camera to slide along its optical axis. This is necessary in order to fascilitate quick balancing of the system when various lenses and accessories are added or removed from the rig.
In turn, the dovetail plate itself is attached to a tripod head or other support. This can be done in two different ways. One way to do this is to clamp the bottom lip (which is also specifically machined to allow this) of the dovetail plate in a specially designed clamp. The second option is to use the variety of 1/4″ and 3/8″ mounting holes to attach the dovetail plate to a quick-release snap plate or another support.