Projectors: Lens Shift Demystified

When buying a new projector, many people tend to consider only the obvious specifications like resolution, throw, etc.. Lens shift is a spec that often slips under the radar, especially among first time buyers, but can be extremely vital.

Basically, lens shift gives you the ability to move the projected image vertically and/or horizontally without changing the physical position of the projector. If a projector does not have lens shift, you may need to continuously adjust the location of the device to get a clear image without any keystoning.

Keystoning? What is that?

When a projector is properly setup, it should produce a perfectly rectangle image on the screen. But, you may have noticed instances where the output has a distinctly trapezoidal shape – wider at the top than the bottom. This happens mostly when the projector is placed at an angle to the screen (like on shorter table) and is called keystoning. Most modern projectors come with in-built digital keystone correction to help resolve this issue. But, digital correction is not very effective and could also lead to a loss in detail.

What are the different types of lens shift I will come across?

There are basically two types of lens shift: horizontal and vertical. Generally, a projector will come with either one or the other. Some high-end models even have both.

Horizontal lens shift allows you to move the projected image from left to right (and vice versa), which allows you to place the projector horizontally off-center from the screen. It has a decent amount of range and allows you to alter the position of the image anywhere from 5% to over 50% along the X-axis. Actual range would vary from model to model. However, horizontal lens shift is not as common as vertical lens shift since most people don’t have a problem horizontally centering the projector.

Vertical lens shift moves the image along the Y-axis, allowing you to place the projector at different heights without worrying about keystoning. Most projectors come with this feature and the shift range varies from a modest half-screen length to more than three screen lengths depending on the model you choose. This feature is especially useful if you are going to ceiling mount the projector where the image has to be thrown downwards towards the screen.

Why should I choose a projector with lens shift?

Variable lens shift is the best way to easily make sure that the projected image stays rectangular, which also makes installation much easier. If your projector does not have this feature, you may have to keeping tweaking the position of the projector for a while in order to find the best position for it. And even then, the best position may not be feasible. With lens shift, you can place the device in the general area you want, and modify the position of the lens to prevent get a clear, sharp and properly dimensioned output.