This new feature available in some projectors makes moving the position of the projection in a few degrees vertical or horizontal, through a movement in the lens and not through digital keystone correction as in, thus avoiding the loss of sharpness. Vertical len shifting is the most popular type of shift because it allows for keystone correction and assist in aligning images when multiple projectors are used stacked on top of one another.

Lens shift provides space to move the lens itself left and right or up and down within the projector housing. This adjustment can be made either manually with a dial or joystick, or mechanically using the menu buttons. This extra space to reposition the lens means greater leeway in the placement of a projector in a room and makes moving the position of the projection in a few degrees vertical or horizontal, through a movement in the lens and not through digital keystone correction as in, thus avoiding the loss of sharpness.

Lens shift was designed to correct placement problems in most situations, but it does have its limitations and boundaries.  Some presentation projectors will correct (or shift) the image more so than others, so a little research might be required if you think you might be faced with more extreme presentation environments.

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. 

Variable Lens Shift, is the best way to keep your image rectangular, unless you can place the projector right where it needs to be in terms of height. Even fixed lens shift (which, as noted earlier) will create a small amount of bowing, but variable lens shift will have different amounts of bowing depending on design, distance of the projector to the screen relative to the projector's vertical position, etc. Lens shift can also be useful for fine-tuning the position of the projected image on your screen.

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