Size Matters

The first step to ensuring that the space is an effective presentation forum where each member of the audience can see the presentation is to select a screen that is the right size. An appropriate screen size is determined by taking both the seating arrangement and dimensions of the room into consideration.

As the material projected has changed-from images to data-the guidelines for sizing a screen have been re-evaluated. A few years ago, the standard practice was to establish the width of the projection screen first. The width of the screen was determined by measuring the distance between the screen to the most distant viewer (MDV) and then dividing by six. Previously, projection screens just needed to be big enough for everyone to see, now they must be big enough for everyone in the space to read and evaluate, including the person sitting in the very back row on the outside edge of the room.

Specify projection screens into the presentation space that are large enough for even the most distant viewer to read.

Today's sizing guidelines recommend that designers begin by determining the height dimension of the screen. The general rule for conference rooms and classrooms is that the screen height should be equal to one-sixth of the distance between the screen and the most distant viewer (MDV). The symbol height on the projection screen must increase one-fourth of an inch for every additional seven feet of viewing distance.

Once a screen height has been established based on the distance between the screen and the most distant audience member, it must be checked against the dimensions of the room. Another general rule for presentation spaces is that the bottom of the screen should be a minimum of 4 feet (48 inches) above the audience floor, allowing those audience members seated in the back of the room to see the entire screen. When specifying a screen onto a project, check to ensure that the suggested height of the screen plus the empty space below the bottom of the screen do not exceed the room's ceiling height.

Once the screen height is established, the width of the screen will be determined by the format of the information that will be projected and its associated aspect ratio. The aspect ratio is a ratio of width to height in which the material was recorded and will be projected.

Match the Appropriate Format

When starting a rental video, as the lights are dimming, the popular disclaimer, "This film has been modified from its original version," will dependably appear before the movie begins. This disclaimer exists because the video format of the movie about to be watched at home on a DVD player has been changed from the film format of the original production shown in the movie theater. Movies are recorded on film that is similar to the film in a still camera. This type of film employs chemical reactions to record the visual information on special material. This differs from video formats that store visual information as electronic signals that are then transmitted to the television via radio waves or coaxial cable.

The reason that format is important to consider when selecting a projection screen is that each format captures visual information in a different size or aspect ratio-the ratio of width to height. Movie film, for example, records images that are over twice as wide as they are high. Video formats that can be played on a standard television screen are almost square. In order to make the projected informationfit cleanly onto the available screen, the format of the projected material must match or fit inside of the dimensions of the projection screen.

Today, there are five common format types available, each with its own respective aspect ratio.

• The Cinemascope format is often the format in which movies are originally filmed. The native aspect ratio here is quite wide. It is 2.35:1, which means that in this format the picture is a little more than twice as wide as it is tall.
• The National Television Standards Committee (NTSC) video format is the format that was initially designed to fit cathode ray televisions and has been the standard broadcast format in the United States, Canada, Japan, and elsewhere since that technology first launched into the market. The aspect ratio for this format is 4:3 or 1.33:1, which means that the width of each picture is 1.33 times greater than the height. This aspect ratio is also referred to as a Full Screen format.
• The Letterbox video format attempts to fit the wide-screen image played in movie theaters into the full-screen format that is accepted by most standard televisions. The result is that the picture is pre- sented in the middle of the television screen with black bars above and below it. The problems with the Letterbox format are two-fold. First, the viewing area available on the television screen is significantly shrunk, which can make it difficult to see, and, second, many viewers are terribly distracted by the black bars above and below the image. It does, however, allow viewers to see everything that the director intended them to see on their standard format television screen. The aspect ratio of the Letterbox format is 1.85:1.
• The High-Definition Television (HDTV) video format allows movies to be played in their original wide-screen format without the black bars around the picture. This aspect ratio of 16:9 or 1.78:1 is also becoming a widely popular computer monitor size.
• The AV or square format refers to square screens. These non-standard aspect ratios do not match standard television screens or computer screen formats. Square screens should only be specified on a project where overhead transparency projectors are used.

There is a new format size popping up in computer monitors and in software platforms that boasts an aspect ratio of 16:10. This particular size allows users to clearly display pre-press materials two-up. To meet this new demand, projectors are being introduced onto the market with a native aspect ratio of 16:10. Projection screens built to this ratio are also readily available.

As explained earlier, the height of the projection screen should be determined first based on the distance between the screen and the most distant viewer. The width of the screen is then determined by applying the native aspect ratio of the projector or the aspect ratio of the format of the material that will be projected.