Inner Workings: Inside a Front Projector

Click the image to see how a front projector is put together

With the prices of flat-panel HDTVs falling faster than the World Series hopes of a Kansas City Royals fan, it's not surprising that front projectors haven't been getting their fair share of attention.

But prices for high-def front projectors have also been in a freefall and might be the best big-screen bargain available. With models now selling for less than $1,000 and with some 1080p models heading down toward the $3,000 mark, a projector paired with a screen measured in feet instead of inches packs some serious, hard-to-beat home theater wallop.

Although front projectors aren't ideal as everyday TVs - for one thing, their costly lamps can burn out quickly with frequent use - models using the same DLP, LCoS, and LCD technologies found in rear-projection TVs are a big improvement over bulky, finicky CRT projectors. And digital projectors aren't just cheaper - they're also lighter and easier to set up and use, and they don't need the constant calibration that older tube-based models required.

Photo Gallery

Take, for example, Optoma's $999 HD70, a single-chip DLP projector with 720p (1,280 x 720 pixel) resolution. Maybe its most important component is the DLP board, which holds a processor, memory, and a DMD (Digital Micromirror Device) chip covered with nearly a million mirrors. Since each mirror represents a single pixel, the total number of mirrors corresponds to the image's resolution. Other key components are the light source (typically a UHP lamp), a projection lens, and the projector's optics, which include a condensing lens, a light (or integrating) rod, and a relay lens. Colors are produced by passing light through a spinning "color wheel." (In more expensive, three-chip models, the light instead passes through a prism that splits it into red, green, and blue, and a separate DMD chip is used for each color.)