Ceiling, Rear, and Tabletop Mounting
One of the first things that you’ll need to decide is how you want to mount the projector. Most projectors today provide several mounting options including: tabletop mounting, rear projector tabletop mounting, and rear projection ceiling mounting.
Table Top Mounting
Projectors were first developed with the business world in mind and because of this, a multitude of business-class functions are readily available to home theater enthusiasts. With that being said, it is important to know that a projector does not shoot an image in a straight line from its lens. It actually shoots the image upward , as shown below.
For example, in a typical business presentation, the presenter sets up a projector and uses it to deliver a presentation. If the projector shot the image straight ahead, half of the image would display above the projector, and the other half would display below the projector, as shown below. Not surprisingly, this would create a problem for the audience trying to view the presentation because the projector itself would block the view of the bottom half of the image. They would literally need to stand up and look over the projector to see the image.
When a projector is tilted upward in order to display a complete image above the projector or above a specified point, the image becomes trapezoidal, where the top of the image is wider than the bottom. This effect is called keystoning and it makes watching a video presentation difficult, if not impossible.
To solve this problem, projector manufacturers use lenses with fixed keystone correction, which shoot images above the projector (first image above). Because this process is not adjustable, it is referred to as fixed keystone correction. Now, some spec sheets list this figure as the degree to which the projector shoots upward. Do not confuse fixed keystone correction with a spec for digital keystone correction or any spec that gives a variable degree of keystone correction. We will discuss digital keystone correction later as it is not recommended for video playback.
Now that you know that projectors shoot upward, it’s time to tell you why this affects how you mount your projector. Fixed keystone correction allows you to place your projector on a tabletop in front of you. It further enables you to place your screen high up for a more theater-like environment.
Ceiling Mounting
Let’s move on to ceiling mounting. Ceiling mounting your projector can be a bit more complicated. Let’s assume that you want to place your projector high on a shelf in the back of your room. If you remember how fixed keystone correction works, you’ll realize that the projector would actually shoot the image onto your ceiling, see below image.
However, projectors combat this problem by enabling you to mount them upside down. If placed near the ceiling, this works out perfectly. The projector will now shoot downward - right at your screen. Okay, so the image will be upside down. You can stand on your head, can’t you?! Don’t panic. Most projectors allow for ceiling mounting so you can easily flip the image right side up using the onscreen menus, see below.
Rear Projection (Behind Screen)
Rear projection table mounting and ceiling mounting work in the same way that front projection does. You still need the same amount of space behind the screen as you would need in front of it, and you still need to allow for keystone correction. But there are some differences. One is that you need a special rear projection screen. Another difference is that you must invert the image and flip it. Fortunately, all of this can be done through the projector’s menu screen. The great thing about rear projection - if you have the space behind a screen to accommodate it - is the advantage that it gives you over ambient light. In a front projection situation, the projector has to shine through ambient light sources such as lamps or sunlight, dimming an image that is already less bright simply because it’s being reflected off a screen. Because there is little to no ambient light behind a rear projection screen and the image isn’t being reflected, it is brighter and less prone to the effects of stray light, making rear projection an excellent option in rooms with minimal light control.