Projector lenses are designed to shoot the image that is slightly above the projector itself. This enables the people viewing the image to clearly see it without getting in the projector’s “line of sight”. Keystoning takes place when the projector is not perpendicular to the screen, or if the screen of the projection has a slightly angled surface. The resulting image looks like a trapeze rather than a square, causing distortion that needs to be avoided. In many cases, projector only has a single place it can be placed at, and that’s where keystone correction comes in.
Manual Keystone Correction
Old projectors do not have keystone correction and they have to be placed in a fixed position, requiring the entire room to be adjusted to accommodate the projector. Most projectors today feature manual keystone correction. The option allows the user to manually adjust the lens of the projector in order to project an angle that is higher or lower than it would actually be if the projector was placed on a flat surface. This kind of correction works great in a lot of situations, but it does not eliminate horizontal keystoning. The disadvantage is that the projector needs to be placed far away from the screen in order to get the best results.
Digital Keystone Correction
New LCD and DLP projectors are digital devices that are able to digitally convert and scale data in order to fit the screen perfectly. These types of projectors usually feature an image altering algorithm that allows them to alter the image prior to it reaching the lens. The result of this is a squared image, even when horizontal and vertical angles are involved. This opens up a whole new world of possibilities when it comes to placing the projector. However, this kind of correction has side effects that might prove to be unavoidable in certain situations. First, by squaring the image in order to correct it, it actually shrinks the longer side of the image by using digital scaling. Information can be removed and unwanted results can appear. The second issue that is likely to occur is the loss of maximum lumen output since the scaled image is actually smaller than the resolution of the display. To counter these issues, vertical or horizontal lens shift is used, depending if the projector is under a horizontal or vertical angle.
What Does Lens Shift Mean
Lens shift is the process of physically shifting the projector’s lens in order to allow the projector to be placed under an angle without affecting the quality of the projected image. For example, vertical shift will move the projected image up or down, while the horizontal shift will move it left or right, allowing you to position the projector higher or lower, or to the sides, respectively. Some better projectors have their lens shift expressed as a ratio or a percentage. Lens shift is useful when a projector is not going to be moved around often, while keystone correction will prove beneficial to those who want more freedom. You can learn more about lens shift here.