Lens Shift: why does this option change everything for your video projector installation?

Installing a video projector in a living room is not necessarily a pleasure: for the image to be rectangular, it must be perfectly aligned facing the center of the screen, the canvas or the wall on which it is projected. The problem is that not all spaces are suitable for placing the device in exactly that ideal location. If keystone correction exists and already makes life easier, lens shift (or lens shift) is even more interesting.

What is lens shift?

The lens shift is a mechanical device that physically moves the optical unit inside the video projector chassis. Thanks to an integrated motor, and with a few clicks on the remote control, the user can slide the image vertically or horizontally on their wall, without ever having to move the projector or tilt it.

The advantages of lens shift compared to keystone correction

To fully understand the interest of this technology, we must compare it to that which already exists today: trapezoid correction, which we see in English under the name of keystone. The vast majority of consumer projectors offer this digital correction to straighten a distorted image when the device is not in front of the screen. It is often even automatic, making installation easier: you can place the video projector aside if you cannot place it perfectly. The problem is that keystone correction is a “destructive” method. To turn a trapezoid into a rectangle, the projector software must remove rows of pixels and recalculate the entire display. This processing inevitably leads to a loss of definition, and your Full HD or 4K image (depending on your model) is no longer really.

Conversely, lens shift is a purely optical solution that preserves the total integrity of the video signal. Since it is the lens that moves and not the image that is recalculated, each pixel of the matrix is ​​used and projected onto the screen. There is therefore no degradation of the definition. You get exactly the image quality promised by the manufacturer, even if your projector is placed on a shelf or attached to a ceiling in a corner.

Another major advantage of lens shift concerns the management of light pollution around the image. When using keystone correction, the pixels “turned off” by the processor to straighten the frame continue to emit a slight light (only Oled TVs can produce ultra-deep blacks), creating a very visible grayish border around the screen, particularly if you are watching a film in the dark. With lens shift, this phenomenon simply does not exist since the entire image coming from the sensor is displaced.

Of course, lens shift has its limits and the angle that can be adjusted is still limited. We can place the video projector a little to the side, but not at the other end of the room either, otherwise it will be necessary to add a keystone correction.

A technology that comes at a price