The complementary component of a multimedia projector installation is the projection screen. Type of screen, screen placement, and screen size can all have an impact on the quality of a presentation. A screen is always essential, since trying to project on a painted wall or hanging cloth always gives marginal to poor results. So, the screen investment should be given careful consideration.

What are the different screen types?
Screen types fall into two families: front projection and rear projection. By far, the front projection format is the most widely used. Front projection makes for a simpler, more straightforward installation. The screen is mounted a certain distance from the projector, and the fabric is extended. A rear projection installation requires specialized accommodations. Rear screens are either solid translucent panels or vinyl translucent "fabric." A solid screen always requires a fixed mounting to support the panel. All rear screen installations require either a deep room behind the screen to accommodate the throw distance of the projector or a complex mirror system to direct and focus the light. The one major advantage of a rear screen projection format is that during a presentation, no shadows are cast on the image if the presenter stands between the screen and audience. However, most needs are usually met by front projection.

What fabrics are available?
The actual surface of a screen is called the fabric, although it can be of materials other than cloth. In the front screen format, there are three styles of fabric available, each designed for different applications.

1. Glass Beaded
This fabric has tiny glass bubbles or "beads" covering its surface and gives the advantage of high reflectivity or "gain." Its use is limited because in order to achieve light gain, the viewing angle width is greatly reduced. This makes it uncomfortable for viewers on the outside perimeter of the screen's reflection, as most of the image light is being reflected straight back and away from them. Glass beaded screens are also difficult to clean without causing damage to the beads.

2. Matte White
This fabric is the best all-around screen material. It can be cleaned with mild soap and water. The light reflectivity gain is referred to as "unity." The angle of viewing is wider, making it more practical for use in areas where viewers may be to one side of the screen. It works well with both video and computer or "data" presentations. There are variations of this screen fabric that can incorporate some of the higher reflectivity of a glass beaded screen without using the beads. The amount of gain is controlled to ensure the viewing angle does not become too narrow. These screens can work well with projectors that have low light output. For most situations, matte white remains the best choice.

3. Silver lenticular
This is a silver matte finish screen that has ridge lines embossed into its surface. The special application of this screen is in areas of direct sunlight where ambient light cannot be controlled. The silver screen is less prone to "washout" than a white fabric screen would be in sunlight.

What size screen should we get and where should we place it?
A screen should be chosen that accommodates the size of the audience and the presentation area. A few basic rules will help you get the best screen/audience match. The screen height should be at least one-sixth the distance from the screen fabric to where the most distant viewer sits. The bottom of the fabric should be no closer than four feet from the floor. This affords those in the back of the audience an unobstructed view. The closest viewer should be no closer than one and a half times the width of the screen.
 
If the furthest viewer is 60 feet from the screen, then the top of the screen should be at least 10 feet high.

The screen should be no closer than four feet to the floor, leaving a vertical screen size of six feet.

If you choose a standard width, such as eight feet wide, the closest viewer should be no closer than 12 feet.

Of course, these are ideals. Higher mounting would be okay, but below four feet may not accommodate those in the back of the audience. Larger screens are not always better, as you may not be able to fill the screen with image, leaving a border around the sides, top, or bottom.

What are some considerations for on-screen images?
The image the audience sees presented on-screen can be outstanding, just by observing a few principals of multimedia projection. Be sure to eliminate any keystoning of the image caused by improper projector/screen alignment. No one wants to see a wedge-shaped presentation where part of the image is out of focus.

Make accommodations to control ambient light. This may require turning some lights off or even repositioning some fixtures. Windows that allow direct sunlight to fall on the screen can present washout problems. Simply changing to a silver matte screen may not be a solution, because the screen may also be used at night. A better solution is repositioning the screen, or controlling the amount of light coming through the windows.

Be sure the contrast and brightness are adjusted properly on the multimedia projector. Many projectors have several pre-set combinations in their menus, all designed to accommodate a particular type of presentation, like a movie or a data presentation.

When building data content for slide show presentations, try to avoid using a fancy, hard-to-read font, and be sure the letters are of sufficient size to allow viewers in the back to see them clearly. The rule of font size is that the distance to the furthest viewer should be no greater than 150 times the character height. So, a displayed six-inch letter or number would be visible back to 75 feet. Try to avoid using letters and backgrounds of similar color or luminance. Yellow letters on a white background would be an example of what to avoid. Try not to make your slides too complex with multiple font/color combinations.

An image concern is always brightness. Light behaves according to what is known as the inverse square law, which basically teaches that if you double your throw distance, there is only one-fourth as much light illuminating the screen, so closer throw distances deliver more image brightness.

If you are displaying multiple formats of media, such as video that may be in either 4:3 ratio or 16:9 ratio, be sure the screen width can accommodate the wider format from the chosen throw distance. The vertical dimension of the screen can always be adjusted by raising or lowering the fabric.

This article is courtesy of Long's Electronics, www.longsav.com.