Editing Scheimpflug principle (section)

==Description==
[[File:DOF-ShallowDepthofField.jpg|thumb|Figure 1. With a normal camera, when the subject is not parallel to the image plane, only a small region is in focus.]]
[[File:Scheimpflug.gif|thumb|Figure 2. The angles of the Scheimpflug principle, using the example of a photographic lens]]
[[File:PoFRotation.png|thumb|Figure 3. Rotation of the plane of focus]]
[[File:ScheimpflugPoFAngle.png|thumb|Figure 4. Rotation-axis distance and angle of the PoF]]

Normally, the lens and image (film or sensor) planes of a camera are parallel, and the [[plane of focus]] (PoF) is parallel to the lens and image planes. If a planar subject (such as the side of a building) is also parallel to the image plane, it can coincide with the PoF, and the entire subject can be rendered sharply. If the subject plane is not parallel to the image plane, it will be in focus only along a line where it intersects the PoF, as illustrated in Figure 1.

But when a lens is tilted with respect to the image plane, an oblique tangent extended from the [[film plane|image plane]] and another extended from the [[photographic lens|lens]] plane meet at a line through which the PoF also passes, as illustrated in Figure 2. With this condition, a planar subject that is not parallel to the image plane can be completely in focus. While many photographers were/are unaware of the exact geometric relationship between the PoF, lens plane, and film plane, swinging and tilting the lens to swing and tilt the PoF was practiced since the middle of the 19th century. But, when Carpentier and Scheimpflug wanted to produce equipment to automate the process, they needed to find a geometric relationship.

Scheimpflug (1904) referenced this concept in his British patent; [[Jules Carpentier|Carpentier]] (1901) also described the concept in an earlier British patent for a perspective-correcting photographic [[enlarger]]. The concept can be inferred from a [[Desargues' theorem|theorem]] in [[projective geometry]] of [[Gérard Desargues]]; the principle also readily derives from simple geometric considerations and application of the Gaussian [[thin lens|thin-lens]] formula, as shown in the section [[#Proof of the Scheimpflug principle|Proof of the Scheimpflug principle]].