Applications
When making photographs of a building or other large structure from the ground, it is often impossible (without shift) to fit the entire building in the frame without tilting the camera upwards. The resultant perspective causes the top of the building to appear smaller than its base, which is often considered undesirable (b). The perspective effect is proportional to the lens’s angle of view.
Photographing from the ground, perspective can be eliminated by keeping the film plane parallel to the building. With ordinary lenses, this results in capturing only the bottom part of the subject (a). With a perspective control lens, however, the lens may be shifted upwards in relation to the image area, placing more of the subject within the frame (c). The ground level, the camera’s point of perspective, is shifted towards the bottom of the frame.
Another use of shifting is in taking pictures of a mirror. By moving the camera off to one side of the mirror, and shifting the lens in the opposite direction, an image of the mirror can be captured without the reflection of the camera or photographer. Shifting can similarly be used to photograph “around” an object, such as a building support in a gallery, without producing an obviously oblique view.
Read more about this topic: Perspective Control Lens