Matte Box Rails
Usually, to remotely control the focus, iris, and/or zoom, operators need a set of motors to drive the lenses. As noted the Preston is one of the standards, which is why we use it. Other devices commonly used are the Cmotion in Europe. All of these motors need to mount to something, and we use the same mount — matte box rails.
A matte box is the funny looking square bellows on the front of the camera lens that makes it look like a movie camera. It keeps lights from hitting the lens directly and “flaring” the lens. Fortunately, there are only about 3 separate standards for matte box “rails”, the rods that all of this stuff is mounted to. There are 2 sizes of rail, 15mm and 19mm, and two sets of spacings for the 15mm rails.
19mm diameter, 104 mm spacing. This is the standard “big camera” rail system on the US East Coast and Europe.
15mm diameter, 100 mm spacing. This is the standard “big camera” rail system usually seen on the US West Coast.
15mm diameter, 60 mm spacing. This is a “video” rail system, typically found on smaller cameras.