How to choose a projection screen

The most important specifications

• Front vs. rear screens. For most purposes, a front projection screen is the obvious choice, simply because it can fit into any room without the need to build a projection booth. Still, a rear screen has advantages. It will permit the use of visuals in near normal room lighting, allowing your audience to take notes and your speaker to maintain eye contact with audience members. No matter what your lighting levels, the effects of ambient light will be reduced, producing images of better contrast. Speakers may walk in front of a rear screen without casting shadows. Finally, the noise and distraction of equipment is eliminated by moving it to a separate room.

• Screen surface. You’ll need to choose a surface with your projection source and lighting conditions in mind. It will determine the sharpness and brightness of your projected image.

  In front projection, matte white surfaces (by far the most popular) offer excellent definition for finely-detailed images, such as computer text, while providing very good images from color slides and overheads. Smooth silver or white pearlescent surfaces provide particularly bright images best for video or computer projection, but are too prone to hotspotting for overheads. Glass beaded surfaces offer a brighter image with some sacrifice of sharpness. They are intended for general video, slide and film projection use, but are not recommended for computer data. Lenticular surfaces are designed for video and slide projection (not for overheads) and for rooms with side light from windows. They work by focusing projected light that would otherwise be disbursed on the vertical axis onto the horizontal where it can be viewed. In the same way, ambient side light that would otherwise mix with the projected image is reflected away.

  In rear projection situations, there are a variety of coatings and screen materials designed for specific situations. Most standard surfaces are best for rooms with a relatively narrow seating cone and good lighting control, with specialty surfaces available when viewing angles will be wide or lighting high. Your United account representative can help you choose the best for your application.

• Gain measures the ability of a screen to gather light from a projector and direct it to a certain location. A high gain screen can be very important in situations where you want to keep room lights high for note taking or discussion, particularly if you can’t keep those lights from washing onto the screen surface.

  There is a trade-off between gain and viewing angles. There’s only so much projected light to go around. A high-gain screen will focus that light toward an audience seated tightly around the horizontal and vertical projection axes; a wide-angle screen will distribute it more evenly, thus providing less light for viewers at the center. No matter how wide the stated viewing angle, gain values will fall as you measure brightness farther from the center axis. How dim an image can appear and still be useable is something of a judgement call, and for this reason the maximum viewing angles given here are only guidelines.

  Gain varies with screen surface. Most matte white screens are rated at a gain of about 1.0, and most glass beaded provide a gain of about 2.5. Lenticular surfaces are rated from 1.5 up to about 3.0, and rear screens offer gains up to 5.0.

  United can supply a number of special high-gain surfaces when the need arises, including some from Stewart Filmscreen which are not described in this catalog. Please call your United account representative if you have such a need.

• Viewing angles. You should be aware that, no matter what a screen’s stated viewing angle, seating an audience outside of a 90° cone has inherent problems that no screen will overcome. At angles greater than 45° from a line perpendicular to the center of your screen, images will appear distorted, with objects looking taller and thinner than they should. Thus most screens are designed to focus projected light back to an audience within that 90° cone, and images viewed from beyond that will appear quite dim.

  Nonetheless, there are situations where wider viewing angles are needed, and United can supply a number of surfaces for wide-angle viewing.

• The flatness of the projection surface is very important if you plan to project computer text, since most projectors have a very narrow plane of focus and will not provide a consistently sharp image on a rippled screen. Obviously, this will not be a problem with a rigid rear screen or even with a fast-fold, but it is a big factor in a wall screen. Tensioning systems physically pull a flexible material straight to greatly improve the image focus.

Useful features

• Keystone correction on a tripod or wall screen tilts the top of the screen forward to minimize rectangular distortion caused by the projector being positioned lower than the center of the screen. Tilting the screen will not always be necessary, as many video projectors have their own correction built in. It’s important, however, with slide, overhead and many LCD projectors.

• Black borders can be very helpful. They provide a crisp edge for any picture, eliminating any wash onto the wall behind your screen and masking any unevenness due to out-of-level projectors. By their contrast with the projected image, they also fool the eye into perceiving the image as brighter and more colorful than it would otherwise be.

• Seamless material is important in larger screens. Many of the larger screens in this catalog will carry a horizontal seem, though United can supply very large seamless screens (and seamless material up to 40’ x 90’). Please call before ordering if this is a consideration.

Beyond the specifications

• Reliability is a key factor, particularly in motorized screens, since a balky screen can stop a presentation. Too, screen repairs can be expensive.

• Delivery time is also important, as most rear screens, motorized screens and certain tripod and wall screens will be made to order, rather than kept in stock, by the manufacturer. If your schedule is tight, you’ll want to order early.

  United typically recommends screens by Da-Lite, Draper and Bretford out of the many brands available, because we’ve had good experiences with delivery, reliability and after-sale support. If you’re considering another brand, be sure to ask about these issues. Remember, the real cost of a poor screen choice is loss of the use of your meeting space while you’re waiting for a repair or replacement.