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The best projector on earth is useless if it doesn't fit in your theater. To make projectors easier to use in a variety of rooms and help them accommodate different screen sizes, many projectors now incorporate long zoom lenses and physical lens shift.
Zoom Range
A zoom lens is able to make the projected image larger or smaller by shifting the internal optical elements of the lens. This allows a projector to deliver the desired image size from a range of throw distances. Some projectors have a very limited zoom range. For example, a 1.20:1 lens, sometimes noted as 1.2x, means the maximum image size is just 20% larger than the minimum size. On the other hand, some projectors have zoom lenses of 2.0:1, or 2.0x, meaning that the maximum image size is double that of the minimum image size. Such a lens provides a lot more flexibility to create the image size you want from the place you want to locate the projector.
Though long zoom ranges offer great flexibility, the projector's potential light output usually drops somewhat if you use the telescopic end of a long zoom lens. Some representative samples have shown lumen loss of 25% to 41% when using the lens's telephoto position, and light output drops off linearly--meaning that it will lose half as much light at the lens's midpoint, and so on. If you want to maximize light output, it is best to avoid the longest throw distance the lens will allow.
In your search for the right projector, first determine the size of the image you want on the wall. Then use the Projection Calculator to see if the model you are looking at will create that size image with the room size and throw distances you have to work with.
Lens Shift
Another feature that makes installation easier is lens shift. Lens shift is the ability to move the projected image up or down, left or right, while keeping the projector stationary. This makes it a great deal easier to place the projector where you want it, and adjust the lens so that the image fits your screen perfectly. If you do not have any lens shift capability, you will need to take extreme care to position the projector at the precise location demanded by its fixed throw angle.
If the projector does not have lens shift, one alternative is to tilt the projector such that the image fills the screen from the position you want to place the projector. However, this will result in a trapezoidal image. You can square it up using keystone correction, but this is something you should avoid if possible. Keystone correction causes the projector to use fewer pixels to display the image, which causes the projector to scale the image to fit the new smaller pixel matrix. This eliminates some of the benefits of using an HD projector to begin with, namely native display of HD signals, resulting in maximum detail and sharpness.
Vertical lens shift, which moves the projected image up and down, allows the projector to be placed at different heights and still properly light up your screen. The range of shift varies by projector, from a modest range of half a screen height to a maximum of about three screen heights. If you plan to install your projector on a rear shelf so that the projector is about the same height as the screen, you only need a modest lens shift range. On the other hand, if you plan on ceiling mounting your projector and having it throw the image downward to the screen, or using a high rear shelf, a more extensive vertical lens shift range is required. Without lens shift, it is sometimes possible to ceiling mount the projector in the precise location dictated by its fixed throw angle. However, this often requires the use of a drop tube to distance the projector from the ceiling to achieve your preferred screen height.
Horizontal lens shift moves the projected image from side to side, allowing the projector to be placed off-center horiontally from the screen. While horizontal lens shift is not normally as extensive in its range as vertical shift, it does allow for some movement, which is crucial if you cannot place your projector in line with the center of your screen. Horizontal lens shift can vary between 5% and over 50% of a projected image's width, and it is less common than vertical shift.
The availability of vertical and/or horizontal lens shift on a given model is noted in ProjectorCentral's database, but the specific range data is not. However, these specifications are always discussed in ProjectorCentral reviews. They can also be found in the Owner's Manuals, many of which are available from the projector's specification page in our database.
