Canon TS-E17MM F/4L Instructions Manual page 12

4. Shift Function
Shifting moves the optical axis of the lens in parallel off the center of the imaging plane.
Shift can be used to good effect in the situations shown below.
●
If you photograph a subject such as a
building with a normal lens, the top of
the building tapers away. But by placing
the camera parallel to the building and
shifting the lens, you can correct this
tapering effect.
●
When you are shooting a reflective
subject, you can move the camera to a
position where the camera does not
appear in the shot and then use shift to
take the picture. This lets you keep the
camera out of the shot without having
to change the shot composition.
ENG-11