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Lens shift is a feature of projectors which enables users to get around the problem of making frequent adjustments to the physical positioning of their projector to ensure that it is always perpendicular to the position of the screen, to avoid distorting and stretching the image.

Lens shift gives users much greater flexibility when deciding where to install their projectors and so it has become a desirable feature to look for when shopping for a new projector. But what exactly is lens shift and how does it work? And where does keystone correction come in?

The term lens shift refers to the positional adjustment of the lens inside the projector. By changing the position of the lens, the projected image can be moved without physically moving the projector. Not only is this an advantage because physically moving or tilting the projector is an annoyance; doing this also causes the shape of the projected image to become somewhat trapezoidal instead of rectangular.

Horizontal lens shift and vertical lens shift

There are two main types of lens shift. While the majority of projectors offer vertical lens shift functionality, more advanced, expensive projectors offer the ability to shift the lens on additional horizontal axis. Horizontal lens shift means that the lens is adjusted to move the image left or right, whereas vertical lens shift means the lens shifts to move the image up and down.

Motorized lens shift vs. manual lens shift

The internal shifting of a projectors'' lens can be executed either manually, by physically turning a dial to move the lens, or the process can be motorized and completed by pressing the projector''s menu buttons or using a remote control. Motorized lens shift is the more popular option since it can be completed from a distance, for example if the projector is mounted on a ceiling.

The benefits of lens shift

The main benefit of lens shift is the flexibility it gives to those people designing a presentation environment. Previously, the projector had to be centred vertically and horizontally on the projection screen to avoid the distortion of the desired image into a trapezoid shape. With lens shift, the projector can be used from different locations without suffering a major decrease in image quality. Projectors used to use keystone correction technology to get around this problem.

What is keystone correction?

Keystoning is when an image has sides that are different widths, caused by the projected image not being perpendicular to the screen. Manual keystone correction involves physically fine-tuning the projector lens to project higher or lower than the projector''s natural angle. However, this does not fix horizontal keystoning, and for manual keystone correction to have an effect the projector needs to be a substantial distance away from the screen. Digital keystone correction on the other hand alters the image before it reaches the lens to resize and correct the image to a desired rectangular shape.

Why is lens shift better than keystone correction?

Instead of altering the position of the lens, keystone correction alters the image itself. While keystone correction does correct the image size, the scaling process also compresses the image. Digital keystoning, unlike lens shift, results in a diminishment in resolution. While these disadvantages are barely noticeable for static presentations or spreadsheets, it can become noticeable and annoying when displaying video.

Even though both techniques degrade the image quality, the picture displayed by a projector which has corrected the image with lens shift will be a better quality than an image corrected using keystone correction.

We hope you enjoyed this article by Projector Source Canada.  For more information, or to purchase a display and projector for your business or home, visit us online at or contact us at 1-800-821-3021.

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