Rotating back
A medium- or large-format camera with a rectangular (that is, not square) frame may have a rotable joint between the body and the film back (or the place where the film-back attaches). This allows the camera to be adjusted for horizontal or vertical pictures without turning the camera body. This is very desirable indeed if the camera uses a waist-level finder (which is very difficult to use with the camera turned). It also keeps the rest of the controls in their familiar and convenient arrangement. The back usually has indents so that it clicks into place vertically or horizontally, and then does not slip accidentally to some intermediate angle.
The rotating back is quite an old invention: the Soho Reflex, a wooden-bodied reflex plate camera, was improved with a rotating back from about 1920. The most familiar example is the Mamiya RB67 (which is named for the feature); it is a particularly good one, because the camera has masks in the reflex finder which automatically move to reflect the orientation of the film-back. However, the rotating back contributes to the large bulk of the camera.
Some large-format cameras are made without a rotating back. In such cases, it is necessary to detach the film-holder (or plate-holder, or roll-film back) turn it and re-attach it. This arrangement is often confusingly called a reversing back.
