2018-07-05 14:03:00

Keystone Correction vs Lens Shift, In Setting Up A Video Projector


 Maybe you are installing a new projector, using your projector in a new environment or are in a situation where you have to use an unfamiliar projector; sometimes you might discover that the image on the projector screen is positioned improperly. The image may not be aligned with the borders of the screen or might extend beyond its borders. Its edges might not be parallel to the border of the screen. The image may not appear rectangular but might have angled edges that form a trapezoid. While settings like focus and zoom can improve the size and sharpness of the images and make them appear more crip, however, they cannot help with such distorted images.

What Causes Image Distortion?

A projector must be installed in such a way so that its front side (the one with lens) is parallel to the screen and its bottom side (base) is perpendicular to the screen. Also, the center of the lens of the projector must be inline with the center of the screen. Sometimes it may not be possible to install a projector perfectly. It is common especially in areas that have space constraints or for aesthetic reasons such as if the owner of the premises wants the projector to stay out of sight.

The images of a projector appearing like a trapezoid are caused by tilting of the projector. If the projector is installed ideally, its bottom surface will be perpendicular to the screen. However, if the front end of the projector is tilted downward or upward, its bottom surface will no longer be perpendicular to the screenor parallel to the ground resulting in trapezoid-like images.


 The frontside (the one with the lens) of the projector must be parallel in relation to the frontside of the projector screen. If the image is not rectangular, then the projector screen might not be exactly parallel to the projector. It causes the projector to produce angled images.

These issues can be addressed by changing the angle of the projector, adjusting its mount or the screen so that they are parallel to each other. However, it may not be possible in an area that has limited space or where the screen and mount can’t be adjusted or reached. Even furniture arrangement might become a limitation affecting the viewing experience of the users.

There are two advanced features specifically designed for addressing these issues and improving the positioning of the image on the projector screen. These are keystone correction and lens shift. By becoming familiar with these two features, you can deal with the issues mentioned previously.

 Keystone Correction 

The Keystone Correction is a commonly found feature on most models of digital projectors available from different brands. It digitally corrects the images that have one side wider and the other side narrower so that they appear as rectangular images. The Keystone correction setting is measured in degrees and it denotes the maximum tilt angle that the projector can correct. The range of keystone correction in degrees may vary from one projector to another. The projector performs keystone correction by digitally rectifying the image using compression and scaling. It proportionally adjusts the pixels for rectifying the image though it impacts image quality.

 There are two Keystone Correction options found in the projectors.

1. Vertical Keystone Correction – The Vertical Keystone Correction feature is found in most digital projectors that support keystone correction. It helps to correct the trapezoid-like images produced by upward or downward tilting of the projector. Users can increase or decrease the keystone setting depending on the direction of the tilt. It is an essential requirement for projectors whose bottom surface will not be perpendicular to the screen (parallel to the ground) but at an angle.


 2. Horizontal Keystone Correction – The Horizontal Keystone Correction is a feature rarely found on most projectors although a few projectors do have it like the JMGO J6S smart projector which comes with both vertical and horizontal keystone correction functions. It can rectify the angled images produced by the projector whose front side is not parallel to the screen. The feature can be handy in projectors that will be installed at an angle to the screen.


 Lens Shift

The Lens Shift feature, just like its name, allows you to move the lens assembly of the projector. In this, the lens of the projector moves as you adjust the settings. The lens shift capability of projectors is represented either in percentage or ratio. The higher the supported percentage or ratio, the more is the correction capability of the projector. Some models of projectors from different brands may have a knob or a dial which can be rotated for centering the image. Higher end models of projectors may enable you to adjust the lens shift setting using a remote. It is beneficial especially when the projector is mounted and you can’t move it. Lens shift technology also causes bowing of the image where in the center of the image may be lower than the corners. However, it is not as prominent and does not affect the viewing experience as much.

 There are two lens shift options available in projectors.

1. Vertical Lens Shift – The VerticalLens Shift options enables you to move the lens of the projector up or down for correcting its top and bottom borders. It is found in most feature-packed projectors and allows you to center the image on the projector screen vertically. It is a great option for projectors whose lens side will not be parallel to the screen.

2. Horizontal Lens Shift – The Horizontal Lens Shift option allows you to move the image left or right for horizontally centering the image on the projector screen and rectifying its left and right borders. Projectors whose lens is not going to be inline with the center of the projector screen but more towards one side should ideally have horizontal lens shift.


 A few projectors might also have the diagonal lens shift capability (also called variable lens shit)that allows you to change the lens position both vertically and horizontally at the same time. Variable lens shift is generally seen in top-end LCD projectors that are quite expensive.

Keystone Correction vs Lens Shift

There are a few major differences between the Keystone Correction and the Lens Shift features found in projectors.

- The keystone correction feature is found on most affordable projectors while the lens shift feature is found on medium or high-end projectors that are relatively costlier.

- Keystone correction adjusts the pixels digitally which lowers the quality of the output images. Lens shift aligns the lens of the projector so that the image appears as it should.

- The keystone correction feature is accessible through remote or the settings menu while the lens shift feature might be available through a dial or knob or a remote depending on the projector.

- The size of the output image with the keystone correction may be less than the resolution of the projector while the lens shift feature does not alter the output image size.

- Keystone correction is measured in degrees while the lens shift correction is measured in percentage or ratio.

- Keystone correction projectors are relatively cheaper and portable while lens shift projectors are expensive but have superior image quality.

When To Buy A Projector With Keystone Correction?

Individuals who are on a tight budget can opt for a projector with keystone correction. These projectors are cheaper and easier on the pocket. Users who are going to be using the projector in different environments can also consider a projector with the keystone correction features. Offices having projectors that are ported from one room to another or individuals who carry a projector with them for presentations at different venues can benefit from a projector with the keystone correction feature.

When To Buy A Projector With Lens Shift?

Premises like schools, offices, bars, and pubs that have their projectors installed permanently should opt for a projector with the lens shift feature. Situations wherein optimum image quality is vital for providing users with an enhanced viewing experience must consider projectors with lens shift. Lens Shift does not scale the images, and therefore the output images retain their quality. These premises include venues that display matches or movies and hometheatres among others.

Ideally, care must be taken to install a projector so that it is perpendicular to the screen and the center of its lens is inline with the center of the projector screen. However, if this is not feasible buyers who have do not want to compromise on the image quality and have the money to spare must opt for lens shift projectors. Individuals looking for a portable and affordable projector can buy one with the keystone correction feature.