Considering Projection HDTV Design - dummies

Considering Projection HDTV Design

By Danny Briere, Pat Hurley

Projection HDTVs have two distinct formats:

  • Rear-projection systems encapsulate the projection system and the screen into a single chassis. These systems beam the TV picture onto the back of the screen.
  • Front-projection systems consist of two pieces: the projector itself and a separate screen. A front-projection system beams the image onto the front side of the screen.

Rear projection

Most projection HDTVs sold today are rear-projection TVs (RPTVs). When compared with front-projection systems, the biggest advantage of the RPTV is simplicity — all the pieces and parts are in one chassis, just as they are in an old-fashioned CRT (cathode-ray tube) TV. So, with an RPTV, there’s no lens adjusting and focusing of the picture on the screen. In fact, with most modern RPTV systems (such as DLP and LCD RPTVs), you don’t even need to align or aim the picture to avoid those awful ghosty images you might have seen on older RPTVs.

Compared with a front-projection HDTV, an RPTV has the following features:

  • Has a large (but relatively smaller) screen: RPTVs typically range from 42 to 70 inches diagonally (they can get bigger, but those are the most common sizes), whereas front-projection systems can fill screens 100 inches or larger.
  • Is generally less expensive: However, the most expensive RPTVs cost more than entry-level front projectors.
  • Is easier to install and set up: For most RPTVs, you simply plug it in and turn it on — that’s it. Even the easiest-to-install front-projection system requires adjustment in the placement of lens and chassis to focus the picture to the right size on your screen.

As far as picture quality is concerned, RPTVs (just like front projectors) can have extraordinary picture quality. The biggest factor, when it comes to picture quality, isn’t so much RPTV versus front projector as it is the type of projection system — and the quality of the individual projector.

The biggest picture shortcoming with most RPTVs revolves around the viewing angle of the RPTV — how far from perpendicular to the screen a viewer can be and still see the picture clearly. Some RPTVs have poor viewing angles, so they’re less than best when viewers are seated far to either side of the HDTV.

The other potential shortcoming of RPTVs is their size — not in terms of screen size, but rather in terms of bulkiness. RPTVs based on traditional CRT technologies can be humongous — taking more of your room than you might be willing to allow.

Most new RPTVs, which use microdisplay technologies such as DLP, are quite slim — barely thicker than flat-panel TVs such as plasmas. You can even find some that are wall-mountable like a plasma or LCD!

These microdisplay RPTVs are perhaps the best bang for your buck in HDTVs, combining a large screen with a slim overall package, and a picture as good as plasma at a lower price. This is particularly true when you start looking at screens of larger sizes (more than 50 inches).

Front projection

When you really have to have a big, BIG screen for your HDTV, you have only one choice: a front-projection system. A front-projection system is really a lot like being at the movies because you see a (possibly silver) screen in front of you, and a projector is situated behind you. In fact, some movie theaters have begun to give up film and install DLP (digital light processing) projectors that are really just souped-up versions of the same projectors you can buy for your home HDTV use.

Because you’re projecting the image across the room and onto a separate screen, theoretically there’s almost no limit to the size of your screen and picture. The only real limit revolves around the brightness of the image put out by the projector. Because a projector must be farther away from a bigger screen (and because it is lighting up a larger physical area), it needs to put out a brighter picture than it would with a smaller screen. Projector brightness is measured in ANSI lumens. Projectors with 500 or so lumens are best on smaller screens or in darker rooms, whereas projectors with 1,000 or more lumens are considered quite bright. Some projectors (usually those designed for PC use) are really bright, throwing out 2,000 or more ANSI lumens. These super-bright projectors have been designed for use in brightly lit rooms (like a conference room at an office), but they can do double duty as projectors for very large screens.

Many front-projection TVs have no built-in TV tuner — neither HDTV/ATSC nor standard-definition/NTSC. So you need to use an external tuner, set-top box, or satellite receiver to watch TV.