Many people have never heard of or seen an HDTV that uses rear projection. Usually, when you think of rear projection TVs, you think of the old and very large Cathode Ray Tube tvs of old. Happily, technology always finds a way to advance.
The new RP TVs are comparable to LCD and Plasma screens, just much much cheaper. There are three major types of Rear Projection TVs: CRT (Cathode Ray Tube), LCD (Liquid Crystal Diode) and DLP (Digital Light Processing). Each has it's own unique strengths and of course, drawbacks. However, the processor doesn't matter so much as the type of projection lens.
There are so many different configurations of projection lenses. For a smaller display, there are less lenses as full screen focus is possible with fewer lenses for the smaller screen. However, in today's market of enormous TV sets, the technology had to catch up somehow.
So, along with multiple lenses for a sharp focus, there are mirrors to sharpen that image further. All the mirror does it to lengthen the focus area for the lens, thus magnifying the image being projected. It's just like a reflecting telescope. The image comes through the lens and is projected onto the mirror, which reflects it to the screen.
The screen itself is the next major element of the rear projection HDTVs. There are two elements to the actual screen that are very distinct and different from other HDTVs. First, the inner surface of the screen is made to magnify the projected image even more than the mirror does. It helps keep the integrity of the image by dispersing the brightness over the whole screen. The outer surface is perhaps the most unusual though. The outside of the screen is the Lenticular surface, and manages the contrast and the integrity of the shapes on the screen. If you were to touch the outside of the screen (which you really shouldn't do under any circumstances) it would feel rough instead of smooth. Other HDTVs are extremely smooth on the outside of the screen, but the Lenticular surface of the rear projection TV is actually etched on the outside.
One of the downfalls of the rear projection HDTV is the size of the thing. The box housing all of these elements has to be large enough to contain them all, while keeping the focal distances just right for a sharp image. These TVs tend to be much larger, with a much larger back than the slim flat panels you are probably used to seeing. This very downfall can work to your advantage, however. If you have a lot of space, but a smaller budget to spend on a TV, a rear projection TV might be perfect for you. You get a high quality image that is comparable to other HDTVs, but rear projection TVs cost less and take up more space. It really depends on what your priorities are.
