What is projector lens shift and why does it matter?
Lenses, Throw Ratios, & Projection Surfaces
Lens shift allows a projectionist to physically move the lens within the projector housing to reposition the image on the screen without moving the entire projector. The key advantage is that lens shift moves the image without introducing geometric distortion (keystoning), which preserves image quality.
More lens shift range means more flexibility in where you can mount or rig the projector relative to the screen. A lens with very limited shift capability is sometimes called an "on axis" lens, meaning the projector must be positioned nearly dead-center to the screen.
Read more about projectors in our Comprehensive Guide to Projectors article.