An Introduction to Projection Technology

Projection television takes home cinema to its ultimate limits. No longer is the viewing experience restricted by the physical constraints imposed by a TV tube. With a front projector system an entire wall of your lounge becomes your TV screen. Movies appear as they would in the auditorium of a cinema. You view in total darkness for the best effect. Although there are some models which incorporate a tuner and audio amplifier, this is rare. To casually watch TV you must use the tuner in your VCR for video and your AV amplifier for sound.

Video projectors fall into two categories. Tubed and LCP (liquid crystal projection). Both have unique advantages that affect installation and performance. The tubed projector is a box sporting three lenses. They focus separate red, green and blue images on to the screen to build a TV image as large as you like. It is this type of projector that is commonly used in cinemas and at public displays. On these models, there's more to the optics than meets the eye. As each lens is on a different axis, the pictures don't naturally overlap. An electronic means for converging the picture is therefore provided and a pattern generator produces a grid which has to be focused and aligned so the squares are geometrically true. The process is repeated for all three tubes. If you're inexperienced it can take many hours and if you move the projector you must start again from scratch.

Consequently, tubed projectors are fixed assets usually installed by experts then rarely touched. As the lenses are wide angle, they provide big pictures close to the screen - typically a 60in picture at 2.5m. Typical mountings include ceiling fixing or even floor mounting in the middle of the room.

Your other projection option is more user-friendly. An LCP can be moved from room to room and requires no more set-up than a slide projector. At the heart of the LCP are a number (usually three) of liquid crystal panels. All are illuminated by a single high-wattage metal halide lamp. A complex series of dichroic reflectors and filters split the spectrally pure white light into rays of red, green and blue. Each of these beams illuminates a liquid crystal panel. The images from the panels converge at the focal point of a single lens. Focus and zoom are provided and on many models are controlled via an IR handset.

The disadvantage of LCP has been the so-called 'chicken-wire' effect. Superimposed upon the image is a criss-cross network of pixels or image elements. It is these individual cells that form the picture and, when magnified by the lens, they can become rather obvious.

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