Classroom Buyer's Guide - Keystone Correction

If you’ve ever looked at a projected image and noticed the image is not rectangular, then you have witnessed a keystoning problem first hand. This problem emerges whenever the projector is not perpendicular to the projection surface. Turn it left, turn it right, tip it up or down and that trapezoidal image you see is keystoning.

If the top and bottom of the image are of different lengths, then vertical lens shift can fix this problem. Without moving the projector, vertical lens shift allows you to raise or lower the image and turn that trapezoid back into a rectangle.

If the left and right of the image are of different lengths, then horizontal lens shift can fix this problem. Again, without moving the projector, horizontal lens shift allows you to move the image left or right and turn that trapezoid back into a rectangle.

If you're acquainted with keystone problems, you might ask, why not use digital keystone correction. This feature is available on just about every projector that ships today and it does "square" the image if the projector is slightly askew. Just be aware that digital keystone correction can have a couple of unwanted side effects that may or may not be an issue for your unique application.

First, it squares the image by shrinking the long side of the image using digital scaling. This means information is removed and the result is that scaling artifacts become evident in the image. For example, text will be a little fuzzy in the scaled area of the image. This fuzziness is less evident if you're projecting video or photos. Second, it causes some loss of lumen output because the scaled image is smaller than the native resolution of the display. So, if you're moving a projector from classroom to classroom or you have room constraints in a fixed installation, vertical and/or horizontal lens shift provides the best solution.

To help you find projectors with horizontal and vertical lens shift, click here. We've preselected these features, but you can change any of the search options to narrow down your search. Use the "Sort by" option to order your results to your needs.