Rear-Projection Television - What You Need To Know 4 - Lens, Mirror, Screen, Box

The previous pages outlined the first basic element of rear-projection televisions; the projection technology used. The remaining four elements in rear-projection television construction are outlined on this page.

Projection Lenses

The second key element in rear-projection television, are the type of lenses used to magnify the projected image. There are usually several lens elements employed. It is usual for a rear-projection television to employ four or five lens elements; some sets employ more. The reason for this is that several successive lens are needed to maintain shape and brightness integrity of the image. It is very easy for a single lens to make things look good in the center of the image, but as the light and image content is dispersed across the area needed for the size of screen employed, additional lens elements are needed to maintain the overall image shape so that objects in the image look the same on the sides and corners as they do in the center of the screen.

In terms of the physical construction of the lens assemblies themselves, all-glass assemblies are the best, especially in terms of withstanding high temperature variations from both internal and external factors. However, many manufacturers use a combination of glass and acrylic-based lens construction. This may not be bad, but there may be differences noticeable not only in the final image, but overall image performance in the long term. Before making a rear-projection television purchase, it may be wise to check the manufacturer's website for information on the type of lenses used in their projection assemblies.

Mirrors

The third element necessary in the design of a rear-projection television is the mirror. Since the projected image has to projected on a large surface within a relatively small space (in comparison to a standard video projector and screen) a mirror is placed in the path of the projection element, magnifying lenses, and the screen. This is enables the projection elements and magnifying lenses to be placed at the bottom of the projection television cabinet. This gives the projected image a longer path to the screen itself so that a larger image can be presented as well redirecting the path of the projected image so that it will be facing the viewer correctly.

The Screen

The fourth element of a rear-projection television is the actual screen upon which the image is seen by viewer. The type of screen used in projection televisions is much different than those used for front video projection or film. A rear-projection television screen is made up of two primary elements. First, there is the inner Fresnel surface, which further magnifies and disperses the brightness of the image across the screen. Second, there is an outer Lenticular surface, which helps in the final shape integrity of the image, as well as contributing to contrast and the wideness of the televisions viewing angle. If you were to touch a rear-projection television screen (which you should never do under normal circumstances) you would notice that its surface is not smooth, as is a standard film or video projection screen. This is because you are actually touching the Lenticular surface etched into the screen itself.

The Box

Of course, the fifth key element of the rear-projection television itself is the box in which all the elements are sealed in. The size of the box is directly related to the size of the screen surface itself. Rear projection televisions can be of any size, but, practically speaking, they come in sizes housing 41-inch to 76-inch screens. The size of the box that is right for you is determined by your room size and/or you actual viewing distance from the television screen. For a good calculator to determine optimum television screen viewing distance, Click Here.