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Projection Screens
By: Wally Dalziel

Most people do not put enough thought into the screen purchase when putting together a projection package.  The size, shape and screen surface are some of the items that need to be considered. One of the most important decisions in screen selection is to determine the correct size of screen based upon:

* The dimensions of the audience area
* The projection format(s) to be used

In some situations, these two questions yield the same answer; in others, they do not and compromises must be made. Here are the key considerations:

Audience Area?
In determining the correct screen size in relation to the audience area, the goal is to make the screen large enough so those in the rear of the audience area can read the subject matter easily, but not so large that those in the front of the audience area have difficulty seeing the full width of the projected image.

Use the following formulas for calculating screen height for maximum legibility.

For 4:3 moving video and entertainment, screen height should be at least 1/6 the distance from the screen to the furthest seat; for charts and data, as in a conference or lecture room, use 1/4; for complex graphics, as in a command/control center, use 1/2.

For 16:9, 1.85:1, or 2.35:1 projection, screen height should equal or exceed 1/3 the distance from the screen to the optimum seat.

Screen width is generally determined by the height of the screen and the projection formats to be used.

Ceiling Height?
The bottom of the screen should be approximately 4048" above the floor in a room with a level floor and several rows of seats. In rooms with theatre seating or only one or two rows, the bottom of the screen should usually be 2436" above the floor. Try to make sure that the lower part of the screen will be visible from all seats. Extra drop may be required to position the screen at a comfortable viewing level in a room with a high ceiling.

Projection Format?
Once you have determined the correct size of screen for the audience area, that size may be modified based upon the type(s) of projection equipment to be used. If the screen will only be used with one type of projector (NTSC video, HDTV, etc.), it is easy to determine exact screen dimensions based upon the projection format of that projector. Projection formats are expressed in terms of aspect ratio, which is the relationship of the height of the projected image to its width.

Surface Types?
For screen surfaces, color and fabric have lot to do with the quality you end up with. Here are some common screen surface types.

Matte White is the most versatile screen surface and the premier choice when ambient light is controllable. It evenly distributes light over a wide viewing area while colors remain bright and life-like, with no shifts in hue.

High Contrast Matte White, designed for moderate output DLP and LCD projectors, is a great choice when video images are the main source of information being projected and where ambient light is moderately controlled.

A Glass Beaded surface has the ability to achieve a higher gain by reflecting more of the projected image back along the projection axis. Glass beads impregnated into the screen's surface provide additional reflectance. This attribute creates an unparalleled screen surface that reproduces vibrant life-like color at moderate viewing angles.

Wally Dalziel is the owner of www.ChurchProjectors.com.

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