Video Projector Setup: Lens Shift vs Keystone Correction

Lens Shift and Keystone Correction Make Video Projector Setup Easier

Keystone Correction vs Lens Shift Examples
Keystone Correction vs Lens Shift Examples. Images provided by Epson

Setting up a video projector and screen seems like it should be an easy task — just put up your screen, place your projector on a table or mount it on the ceiling, point the lens at the screen, plug it in, turn it on, and you are set to go.

However, after you get everything set-up and turn the projector on, you may find that the image is not positioned on the screen properly (off center, too high, or too low), or the shape of the image is not even on all sides.

Of course, the projector may have Focus and Zoom controls that can help to get the image to look right in terms of the desired sharpness and size, but if the angle of the projector's lens is not lined up properly with the projection screen, the image may not fall within the borders of the screen, or you may not be able to get the proper rectangular shape of the image on the screen correct.

To correct this, you can use any provided adjustment feet or move the angle of the ceiling mount, but those aren't the only tools that may be needed. Access to Lens Shift and/or Keystone Correction controls are also helpful tools to get the image on your screen to look right.

Lens Shift

Lens Shift is a feature that allows you to physically move the lens assembly of the projector vertically, horizontally, or diagonally without having to move the entire projector.

Some projectors may provide one, two, or all three options, with vertical lens shift being the most common. Depending on the projector, this feature may be accessed using a physical dial or knob, and on more expensive projectors, Lens Shift may also be accessible via the remote control.

By shifting the lens position of the projector internally (sort of like sliding the lens around on a track), you can raise, lower, or re-position the projected image without changing the angle relationship between the projector and the screen. If the problem is simply that your projected image spills over to one side or the top or bottom of the screen, but is otherwise focused, zoomed, and proportionally correct, lens shift reduces the need to physically move the entire projector horizontally or vertically to fit the image within the borders of the screen.

Keystone Correction

Keystone Correction (also referred to as Digital Keystone Correction) is a tool that is also found on a number of video projectors that can aid in getting the image to look correct on the screen but it is different than lens shift.

While lens shift works well if the projector's lens is perpendicular to the screen, keystone correction may be necessary if it is not possible to get the correct lens-to-screen angle so that the image looks like an even rectangle on all sides. In other words, your projected image may be wider or narrower at the top than on the bottom, or it may be wider or narrower on one side than on the other.

What keystone correction does is allow you to manipulate the projected image vertically and/or horizontally so that you can get it as close to appearing as an even rectangle as possible. However, unlike lens shift, this is not done by physically moving the lens up and down or back and forth, instead, keystone correction is performed digitally before the image passes through the lens, and is accessed by projector's on-screen menu function, or via a dedicated control button on the projector or remote control.

It must also be pointed out that while digital keystone correction technology allows for both vertical and horizontal image manipulation, not all projectors that have this feature or offer both options.

Also, since keystone correction is a digital process, it uses compression and scaling to manipulate the shape of the projected image which can result in decreased resolution, artifacts, and often, the results are still not perfect. This means you may still have image shape distortion along the edges of the projected image.

The Bottom Line

Although lens shift and digital keystone correction are both useful tools in video projector setup, it is desirable to not have to use either of them if at all possible as it adds to setup time and may not always solve the entire projector-to-screen angle issue.

When planning a video projector setup, take note where the screen will be placed in relation to the projector and avoid the need for off-center or off-angle projector placement.

However, if the video projector has to be placed in a such a way where the screen angle is not ideal, which is especially common in classroom and business meeting settings, when shopping for your projector check to see if lens shift and/or keystone correction is provided. It is important to note that not all video projectors incorporate these tools, or may just include one of them.

Of course, there are other things you need know before you buy a video projector and screen, such as whether a standard or short-throw projector might work best in your space or whether a video projector or a TV is better suited to your needs based on lighting conditions or screen size, should also be considered.