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Comparing Keystone Correction vs. Lens Shift


Keystone correction and Lens shift are common terms used when it comes to the projector. Each of these features allows you to make adjustments to an image, even though they do so in different ways.

They are different, and you will get to know the reason for this as you read on. First, let’s look at each of these projector features individually.

Keystone correction

keystone correction in projector

This is a feature that helps to correct keystone effects in projectors. The keystone effect happens when the projector is placed at an angle to the screen or is not perpendicular to the screen, resulting in a trapezoidal-shaped image instead of a perfect rectangle or square.

The image appears skewed or tilted on the screen and would require an adjustment to set it back in place. Keystone correction is the procedure used to make this adjustment.

It could be either vertical or horizontal depending on the side of the image which is to be adjusted. In vertical Keystone correction, you adjust the top and bottom of the image while in horizontal keystone correction you adjust the left and right sides of the image.

You could do a keystone correction manually or automatically. The type of projector that you are using will determine the type of Keystone correction that you can do.

In the manual method, you make use of the keystone correction buttons on your projector or remote control. The buttons have a trapezoidal shape on them, and they also have arrows that point in different directions indicating which side the adjustment will be made. Click on the button that has the arrow pointing to the side that you want to adjust: whether up, down, left or right.

In the automatic method of Keystone correction, there is no need to adjust the sides individually. The projector automatically squares the image by using an infra-red beam and an image altering algorithm. For projectors that enable digital keystone correction, there is usually a button on the projector, to make this adjustment.

Lens shift

lens shift in projector

This is different from Keystone correction. Lens shift allows you to move the lens of the projector physically. In this mechanism, the projector’s lens can move in different directions: up, down, left, and right, but the geometry of the image is not distorted.

Lens Shift can also be vertical or horizontal, although not all projectors support both. Some projectors support only vertical lens shift, while some others support only horizontal lens shift. Some other projectors have a fixed angle for the lens offset.

In Lens shift, there is a reference point which is usually the center of the screen, and this allows the projector to be fixed perpendicular to the screen. Therefore, lens shift will be an offset from the vertical center of a particular screen.

For vertical lens shift, you can move the projector’s lens up or down. This method of lens shift allows you to center the image vertically on the projector screen. While for horizontal lens shift, you can move the lens from left to right, and center the image horizontally to the screen.

Using a knob that is located on the projector, or a dial, you can move the lens up or down as well as side-to-side without having to move the projector itself. The Lens shift feature can also be accessed using the remote control, although this is usually found in high-end models of projectors.

Keystone correction vs. Lens shift: How do they differ?

keystone correction vs lens shift

When you need them

Keystone correction is needed when the projector is not perpendicular to the screen and thus causes a tilted image. In this case, the image has an odd angle, and usually one of the sides is bigger than the other. If you are unable to refocus the image, then Keystone correction may be the only option.

However, for Lens shift, the projector is perpendicular to the screen. There is less work to do, and the adjustment is not in the image but the projector’s optics.

How they affect image quality

Keystone correction alters the image quality to a large extent. This is because a compression mechanism is involved in this process. The number of pixels on the image gets reduced and this results in a lower image resolution. The edges of the image are mostly affected because they are more affected. Artifacts and several other distortions are also likely to occur.

On the other hand, Lens shift does not affect image geometry. It only moves the lens from one position to another. It allows the image to fit onto the screen when the projector is placed either above or below the vertical center of the image, so no artifact is produced.

Lens Shift Capabilities in Digital Projection Projectors

Keystone correction and Lens shift: Are they similar?

These two features are similar because they both enable changes to the shape and location of the projected image, and they make these changes without altering the angle of your screen or moving the projector itself.

Conclusion

Considering their effects on image quality and resolution, Lens shift is preferable to Keystone correction. It helps to ensure optimal picture quality, uniform luminance, and a reasonable contrast and brightness as well.

It is not advisable to use both Keystone correction and lens shift on an image. This will result in lower image quality and cause more artifacts and distortions.


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