Vertical lens shift allows the projector to optically move — or shift — the image up and down so the projector will always be properly placed, even in varying installation scenarios.
Unlike digital keystone correction, lens shift does not degrade the image quality and can be used at will. Lens shift can enable a projector to be placed upon a shelf high up in a room without inverting the projector.
Horizontal lens shift works in exactly the same way except it will allow the projector to move the image from side to side so that the projector doesn’t have to be placed directly in front of where the image should be.
An example of Vertical Lens Shift