The only reason for
tilting and/or swinging the plane of the lens is to reposition the plane
of sharp focus within a scenethe shape of the subject does not change.
You can also control the plane of sharp focus by swinging or tilting the
camera back, but as we've seen, any angular movement of the back standard
also alters the shape of the subject.
you stand facing the side of the camera and draw an imaginary line through
each of the planes of the subject, lens. and film. you will find that
these three planes meet along a common line. This relationship of the
convergence of the three planes is known as the Scheimpflug rulenamed
after Theodor Scheimpflug, the Austrian surveyor who first discovered
the principle in 1894. Scheimpflug observed that when these three planes
met on a common line, the entire image was sharp from near to far, even
at full aperture. Keeping this principle in mind can be very useful in
finding the proper amount of lens and back tilt needed to give maximum
sharpness for a given scene.