Selecting the right projection screen

Screens are an essential part of a display system. It is the screen that delivers the message. A good screen will compliment and enhance the quality of any projected image. And that is important in getting your message across to all in the audience.

Developments in software and electronics have made a large contribution to the enormous steps forward in projectors. Because projectors provide increasingly enhanced light output, contrast and resolution, the quality of the projected image is constantly improving. However, a good projector on its own is not enough. Optimal image quality can only be achieved if the projector and projection screen are matched to each other and to the application. For that reason, selection of the right screen and screen fabric is an essential step for ensuring the best projection result.

The most important selection criteria are explained below. Given that every situation is unique, this information should be regarded only as a guideline.

Step 1. Screen type
Determination of the type of screen is the first step. Selection of a portable, wall or ceiling mounted screen - electrically driven or manual - depends on the situation and your personal preference. Generally speaking, if the projection location is permanent, a wall or ceiling screen is to be preferred. A portable screen is a better choice if you want to be able to project at various locations.

Step 2. Screen size
An important aspect of a projection screen is the screen size. Since presentations now increasingly involve projection of data, the screen should not only be big enough for everything to be seen but, more importantly, for the texts and figures to be read clearly. The correct screen size can be determined using the following three rules of thumb:
- The height of the screen should be at least one sixth of the distance from the screen to the back row of seats.
- The distance from the bottom of the screen to the floor should be at least 125 cm.
- The front row of seats should be around twice the screen height away from the screen.

Step 3. Screen format
Depending on the projector type, the projected image has a given ratio of width to height, also known as the aspect ratio. For a good-looking result, it is recommended to use a projection screen with the same aspect ratio as the projected image. All screens in standard format have two borders on each side, while video or HDTV formats are finished with black borders all around. These black borders increase the perceived contrast and set the projected image off in an attractive manner. Projecta supplies projection screens in the following screen formats:

Step 4. The correct screen fabric
However good the projector might be, the audience will only be properly served if they can clearly see and read the projected image which reaches them. And that is exactly the added value of the projection screen. A projection screen does more than just reflect. It is capable of reflecting and distributing the projected image in a given direction. Why should the image be distributed over the entire room if the audience is seated in a particular area?

The ability of the screen to distribute light in a given direction has direct consequences for the viewing angle and the brightness of the image. This perceived brightness is often referred to as the reflection value or gain. A screen with a wide viewing angle distributes light evenly over a wide viewing area and offers limited gain. Screens with a smaller viewing angle offer a higher gain factor.

Thus, the right choice of screen fabric depends directly on the application. A number of ambient factors also play a role. The most important of these factors are:

• Projector
  Each projector has its own specific light output (ANSI Lumen). Depending on the light output, a higher or lower reflection value may be desirable. If different projection methods are used, the screen fabric should be matched to the projection method with the lowest light output.
• Ambient light
  All the light that does not come from the projector can have a negative influence on the image quality. In applications where the ambient light can not be controlled, a screen fabric with a higher gain is recommended.
• Position of the projector
  Depending on whether the projector is mounted to the ceiling or placed on a projector stand, a ‘reflective’ or 'retro-reflective' screen fabric needs to be selected. For a full explanation, see ”Screen fabrics and characteristics”.
• Projection room
  The arrangement of the seats determines the angle at which the viewers look at the image. The wider this arrangement, the greater the viewing angle of the recommended fabric type needs to be.

This content was copied from http://www.projecta.nl/imagekey.htm