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Projection Screens

The following factors should be considered when purchasing a screen:-

Mechanical Factors
These include the mounting hardware and the type of roller assembly. Mounting hardware with some screens is such that it cannot be positioned tight to the wall. Some roller mechanisms require constant tension on the screen to keep it in position - this can lead to distortion of the screen over time, and is also less convenient than mechanisms which hold the screen in the position to which it is unrolled.

Screen size will necessarily be a compromise in a church installation. Particularly in a traditional church, a large screen may well look out of place. A screen size which is too small will be impossible to read for people at a distance, whereas a large screen will be difficult for those who are too close to it - especially if it is at a height above them. (Minimum recommended viewing distance should be at least 1.5 times the height of the screen - maximum recommended is 6 times the height of the screen).

Screen Material
There are a variety of screen materials available, the most common two being PVC or similar plastics, and fibreglass. (Cotton may also be used). Fibreglass screens are obviously stronger than the cheaper plastic types, and hold their shape better over time. They are less inclined to curl at the edges. It is also important to select a seamless screen, as some manufacturers have welds in the plastic to reduce manufacturing costs, but the joins are visible, and become more obvious as the screen ages.

Screen Surface
The screen surface is an important element in determining how visible a projected image will be. As a rule, the more reflective a screen is (screen "gain"), the narrower the viewing angle will be. Screen surfaces fall into three categories - diffusion, reflective, and retro-reflective. Diffusion screens have a gain of 1, and can be used in virtually any circumstances, provided bright light (apart from the projector!) does not illuminate them. Reflective screens with a gain of around 2, are best used when the projector can be mounted at high level above the screen - they appear brighter, but have a slightly narrower field of vision. Retro-reflective screens (gain around 2.8) have tiny beads - usually glass - embedded in the screen and appear to be very bright. Unfortunately they suffer from very narrow fields of vision.

Research has shown that under normal circumstances, 400 lux of reflected light from a screen is a reasonable level for showing images under typical ambient light levels. Lux = Light Output (in lumens) x Screen Gain, divided by Screen Area.


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