Front Projection Screens - Viewing Surfaces
Courtesy of Draper, Inc.
Front projection screens are available with a wide variety of viewing surfaces, most of which fall into a few categories. Here are descriptions of some general types. Some of these viewing surface types may not be available from all projection screen manufacturers.
First, let's look at two basic ways projection screen surfaces can be made:
Textile Backed Screen Material—Textile-backed screen surfaces are usually mounted on a roller without a tensioning system. The reflective surface is laminated to a woven textile base (usually fiberglass). These surfaces generally cannot be tensioned. The screen surface hangs suitably flat without tensioning because of the stability of the material and the weight of the bottom dowel. Good for all types of projection. Commonly used for single lens video projection, as well as for CRT video and data-graphics projection.
100% Vinyl Screen Material—These screen surfaces are tensioned vinyl with no backing. Available only on motorized, crank-operated and fixed screens that are equipped with a tensioning system. Advantage—The surface is stretched perfectly flat, resulting in better picture quality. Flatness is always desirable and highly recommended for CRT video or data-graphics projection.
The following is a list of projection screen surface types based on their optical qualities. Some of these are typically made with either a textile backed or 100% vinyl construction, while other types are available in both configurations.
Matt white—The standard to which all other screen surfaces are compared. A matt white surface diffuses projected light in all directions, so the image can be seen from any angle. Provides accurate color rendition and superior clarity. Recommended for use with all high light output projection devices. Requires control of ambient light in the audience area. Available with fiberglass backing for free-hanging screens, or in 100% vinyl for tensioned screens.
Glass beaded—A glass beaded viewing surface generally consists of a fiberglass matt white substrate, to which a uniform covering of spherical glass beads has been adhered. The effect is brighter on-axis viewing than matt white surfaces within a narrower viewing cone. The beads are not as smooth as a matt white surface, so there is some loss of clarity and resolution. The optics of a sphere cause the projected light to be reflected directly toward its source, so a glass beaded surface works best when the projector is mounted at or near the audience's eye level. Not recommended for use with ceiling or floor mounted projectors. Glass beaded surfaces cannot be cleaned.
Acoustically transparent—Acoustically transparent screen surfaces have tiny holes to allow sound to pass through the surface, so that speakers can be located directly behind the screen and still perform well. The best acoustically transparent surfaces are similar in gain performance to standard matt white. Some acoustically transparent viewing surfaces are 100% vinyl, requiring a tensioning system. Others have fiberglass content permitting them to be used on a wide range of screen models. Most acoustically transparent screens have a slightly lower resolution than other viewing surfaces.
Moderate contrast—Some viewing surfaces are similar to matt white, with increased contrast and gain, within a narrower viewing cone. Consider a moderate-contrast surface for data-graphics projectors producing 1000 ANSI lumens or less. These surfaces are generally unbacked vinyl, so they require tensioning systems, and have smooth surfaces, for good resolution. Moderate-contrast surfaces usually tolerate a slightly higher ambient light level than matt white.
Grey high contrast—Grey front projection surfaces began to grow in popularity about two years ago, in response to the increasing availability (and affordability) of brilliant LCD and DLP projectors. Grey surfaces provide much better contrast and black reproduction than standard surfaces, with a lower gain. The grey color enhances black levels in the projected image, so the whites appear brighter. A grey viewing surface usually allows for more ambient light in the audience area than traditional surfaces. Grey viewing surfaces are available with and without fiberglass backing.