Sorry Neuro but on this on you're not right. It is the scheimpflug principle, but not from the way around you're thinking about it. The shift part of the lens allows the film plane to remain parallel with the subject, so that there is no need to tilt the camera (and thus the film plane) relative to the subject. Tilting the camera is no different to tilting the lens as far as scheimpflug goes.
Sorry, but that's where you are incorrect. Tilting a camera back
, as in a view camera where the back could be tilted relative to the lens - that's no different than tilting a lens as far as the Scheimpflug principle is concerned. But tilting an SLR, where the film/sensor plane cannot move independently of the lens mount - that's not the Scheimpflug principle.
It might be semantics, but the Scheimpflug principle applies when the lens plane and the image plane are not parallel. That's the key point - for the Scheimpflug principle to apply, the lens plane and the image plane must be tilted with respect to one another. When you angle a camera upward to shoot a tall building, the lens plane and image plane are still parallel, but your desired subject
plane is not parallel to those, and keystoning results. Shift corrects that perspective distortion but maintains the parallel relationship of the lens and image planes, therefore it does not operate through the use of the Scheimpflug principle.
From the Wikipedia article on tilt/shift photography
: ""Tilt-shift" actually encompasses two different types of movements: rotation of the lens plane relative to the image plane, called tilt, and movement of the lens parallel to the image plane, called shift. Tilt is used to control the orientation of the plane of focus (PoF), and hence the part of an image that appears sharp; it makes use of the Scheimpflug principle. Shift is used to adjust the position of the subject in the image area without moving the camera back; this is often helpful in avoiding the convergence of parallel lines, as when photographing tall buildings.
" Put more succinctly, tilt employs the Scheimpflug principle, and shift does not.