Video Projectors: Lens Shift vs. Keystone Correction

Setting up up a video projector and screen can be challenging. Most projectors come with focus and zoom controls to help project an image of the right size and sharpness. You can also use the projector's adjustment feet or move the angle of the ceiling mount to make sure the image falls where it should. Failing that, use lens shift or keystone correction controls to correct the display image. While both can correct a faulty projection, they serve different purposes.

Lens Shift vs. Keystone Correction

Both lens shift and keystone correction allow you to make changes to the shape and location of the projected image without having to relocate the projector. While most video projectors include keystone correction, cheap projectors generally do not include lens shift as an additional option.

Lens shift allows you to physically move the projector's lens assembly up, down, side-to-side, or diagonally without moving the projector. Keystone correction (also referred to as Digital Keystone Correction) digitally manipulates the image before it passes through the lens. It is intended for situations where the projector is not perpendicular to the screen, resulting in an uneven, trapezoidal image.

Lens Shift Pros and Cons

It's always better to correct image problems at the source by adjusting the placement of the lens itself. Projectors with lens shift functionality allow you to move the lens itself—independent of the projector body. You can move the lens assembly up, down, side-to-side, or diagonally without moving the projector.

Most projectors that provide lens shift allow you to move the lens with a physical knob or dial. Some high-end projectors have motorized parts that allow you to shift the lens with a remote control. The feature is generally reserved for pricier video projectors, but it may be worth the investment if you expect a difficult setup process.

Keystone Correction Pros and Cons

Keystone correction changes the image from the source to create an even, rectangular image. It is accessed through the projector's on-screen menu or a dedicated control button on the projector or remote control. While digital keystone correction technology allows for both vertical and horizontal image manipulation, not all projectors include both options.

Since keystone correction is a digital process, it uses compression and scaling to manipulate the shape of the projected image. This can result in artifacts, image distortion, or decreased resolution.

Final Verdict

If the projector is properly aligned with the screen at a perpendicular angle, you can probably fix the problem with lens shift. If the projector is at an odd angle with the screen, resulting in an image that is wide or narrow on one side, use keystone correction.

Although lens shift and digital keystone correction can be useful, they should be viewed as last-resort options. If possible, address image alignment issues when installing the projector.

If you're shopping for a projector that will be placed in an environment with location restrictions—like a classroom or meeting room—see if it has lens shift or keystone correction before you buy it. You might also consider getting a standard or short-throw projector for small spaces, or a TV that's suited for home theaters.