On a regular camera, the image plane (containing the film or image sensor), lens plane, and object plane are parallel, and objects in sharp focus are all at the same distance from the camera. When the lens plane is tilted relative to the image plane, the plane of focus (PoF) is at an angle to the image plane, and objects at different distances from the camera can all be sharply focused if they lie on a straight line. With the lens tilted, the image plane, lens plane, and PoF intersect at a common line; this behavior has become known as the Scheimpflug principle.
When the PoF coincides with an essentially flat subject, the entire subject is sharp; in applications such as landscape photography, getting everything sharp is often the objective.
The PoF can also be oriented so that only a small part of it passes through the subject, producing a very shallow region of sharpness, and the effect is quite different from that obtained simply by using a large aperture with a regular camera. It can be used to make a large scene appear much smaller, as the shallow depth of field is similar to that achieved by a macro lens on miniature subjects.
View camera users usually distinguish between rotating the lens about a horizontal axis (tilt), and rotation about a vertical axis (swing); small- and medium-format camera users often refer to either rotation as “tilt”.