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Projection ScreensVideo Projection screens Projection screens are installations consisting of blank surface and a support structure used for displaying a projected image for and audience to view. Projection screens may be permanently installed as found in a movie theater, painted on the wall, or mobile. Uniformly white or grey screens are used almost exclusively as to avoid any discoloration of the image, while the most desired brightness of the screen depends on a number of variables, such as the ambient light level and the projector light power of the image source. Screens can be further designed for front or rear projection, the more common front projection systems have the image source situated on the same side of the screen as the audience.
Screen typesRigid wall-mounted screens maintain their geometry perfectly just like the big movie screens, which makes them suitable for applications that demand exact reproduction of image geometry. In the church environment the rigid screen works well because the screens are usually always being used when people are present for the service. Such screens are often used in along with the pull-down screens.
Pull-down screens or manual wall Screens are often used in spaces where a permanently installed screen would require too much space. These commonly use vinyl fabric that is rolled in the screen case when not used, making them less visible when the screen is not in use.
Electric screens are wall mounted, ceiling mounted or ceiling recessed. Electric screens are similar to pull-down screens; an electric motor raises and lowers the screen. Electric screens are usually raised or lowered using either a remote control or wall-mounted switch.
Both mobile and permanently installed pull-down screens will be of tensioned or not tensioned variety. Tensioned models attempt to keep the fabric flat and immobile, whereas the not tensioned models have the fabric of the screen hanging freely from their support.
Screen geometry and opticsThe most popular aspect ratio is 4:3 (common video) and widescreen ratio is16:9 (letter box), which are often used as dedicated data projection and home cinema use, respectively. Most churches us 4:3 video aspect ratio.
Gray vs White-ScreensA recent method of improving the perceived image quality is the introduction of gray screens, which are more capable of darker tones than their white counterparts. A gray screen reflects less light, both light from the projector and ambient light. This decreases the luminance (brightness) of both the projected image and ambient light. The light areas of the projected image are dimmer and the dark areas are darker; white is less bright, but intended black is closer to actual black. Many screen manufacturers thus appropriately call their gray screens "high-contrast" models. If a gray screen is chosen a projector with 20% highter ANCI should be considered.
In a church, the projection screen is reflective, whereas the surroundings are not. The ambient light level affects the overall reflectivity of the screen, as well as that of the surroundings. The location of the room fixtures and light levels need to be designed to maximize the projected image on the screen and not be in competition with it.
In most case a standard white screen will meet the needs of a church if ambient lighting levels are adjusted to accommodate and optimize the video picture.
Rear projection verses front projectionThe church using a rear projection screen is superior to the more familiar front screen choices. Here are the advantages:
A rear screen is aesthetically attractive because you can take the projector and all of its additional equipment and hide them away. Space and sight lines are thereby improved in the church.
In addition to that physical advantage, rear screens provide a large variety of optical benefits. The selection may be simplified, however, if we reduce it to a few, basic principles. The first of these is that rear screens utilize refraction to control and manipulate the light passing through them while all front screens depend largely on reflection. All the lighting in the church is now in competition with the front projection system and brightness and color quality can be reduced. An advantage of rear projection is the amount of light output required of the projector need not be as high as in front projection.
If space behind the projection screen is limited the image from the projector may be bounced off one or two mirrors to reduce the length of space behind the in wall screen.