Tilt-shift Photography

Shift
In a subject plane parallel to the image plane, parallel lines in the subject remain parallel in the image. If the image plane is not parallel to the subject, as when pointing a camera up to photograph a tall building, parallel lines converge, and the result sometimes appears unnatural, such as a building that appears to be leaning backwards.
Shift is a displacement of the lens parallel to the image plane that allows adjusting the position of the subject in the image area without moving the camera back; in effect the camera can be aimed with the shift movement. Shift can be used to keep the image plane (and thus focus) parallel to the subject; it can be used to photograph a tall building while keeping the sides of the building parallel. The lens can also be shifted in the opposite direction and the camera tilted up to accentuate the convergence for artistic effect.
Shifting a lens allows different portions of the image circle to be cast onto the image plane, similar to cropping an area along the edge of an image.