Fixed-pixel pitfalls
If you're not willing to install a large, heavy CRT projector, you'll find two other common types of projectors: liquid crystal display (LCD) and digital light processing (DLP). Neither of these suffers from the same problems as CRT-based projectors, but the newer technologies do bring some new problems. Both LCD- and DLP-based projectors have plenty of light output to drive big screens. In fact, in the case of DLP projectors, you'll have light output to burn, so to speak.
 The image above approximates the screen door effect, which occurs when you shine an LCD or DLP projector at too large a screen or sit too close to the screen. |
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LCD and DLP projectors are fixed-pixel displays. Rather than creating a video image by scanning an electron beam from left to right (the lines you see when you put your face too close to your TV), with these systems, individual pixels make up the structure of the picture. When you blow up an image on a giant screen then, these pixels become increasingly visible. Very high-resolution LCD and DLP projectors can, of course, project a larger image without the pixel elements becoming visible. But even the highest-resolution LCD and DLP projectors will show the structure of the picture when projecting too large an image.
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 Calculate the distance between your couch and the screen by multiplying the height of the screen by 3 or 4. |
The most common resolutions of both LCD and DLP projectors are 800x600 pixels and 1,024x768 pixels. For high-end, high-resolution projectors, a good rule of thumb would be to use a screen that's no wider than 84 inches. For best results with other 4:3 LCD and DLP projectors, stick with an 84-inch-diagonal, 4:3 aspect-ratio screen. If you start to go beyond these recommendations, you'll get what is commonly referred to as the screen door effect. It's literally like looking through a screen door. You'll see the little square pixels or mirrors that make up the structure of the picture, which is very distracting. The severity of this effect depends upon how far you're sitting from the screen.
Going the distance
The last thing to take into consideration when deciding on the size of the screen you want for any projector is how far you'll be sitting from the screen. There are some basic guidelines to consider here: Assuming there will be video processing (line doubling, tripling, scaling, and so forth), you would multiply the height of the screen by three or four to determine the correct distance between your chair and the screen. Grab a calculator, and follow along with this example: With a 7-inch or 8-inch CRT projector using the ideal screen width of 72 inches, you would multiply 40.5 inches (the height of a 72-inch-wide, 16:9 screen) by three. You'll find that, ideally, you should be seated about 121.5 to 162 inches--or 10 to 13.5 feet--from the screen. Provided that you have a high-quality projector with good video processing, this arrangement should yield excellent results. To further minimise the screen door effect with DLP and LCD projectors, multiply the height of the screen by four rather than three.
So do yourself--and your projector--a favor and resist the temptation to go with a monster-sized screen just because it's big. Take into serious consideration the type of projector you will be using, the room constraints, and the seating distance from the screen. Once all that is out of the way, you can start planning where to put the ticket office.
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