Lens Tilt Animation
The graphic below illustrates rotation of the plane of sharp focus as the lens focus distance is adjusted, thus moving the image plane with respect to the lens.
The Scheimpflug principle indicates that the plane of sharp focus must pass through: (1) the intersection of the image plane and the lens plane; and (2) the intersection of the front focal plane and a plane through the centre of the lens parallel with the image plane. The position of the latter (called the "hinge line") depends only on the lens tilt and focal length, so does not move when distance of focus is adjusted
Theta (θ) is the angle of tilt set on the lens. This places the "hinge line" a distance J below the lens, where J = focal length / sin θ. As lens focus distance is adjusted, the plane of focus rotates around the hinge line.