Choosing a video projection screen seems like a simple task. Beyond knowing screen size and the type of mount, how much more complicated can it be? After all, it's just a bit of white reflective cloth, right?

Wrong.

A projector screen must be carefully chosen to work specifically with the projector technology that will be used, the room geometry, seating arrangements, projector placement, and level of ambient light, just to name a few of the important factors. Choose poorly, and you'll disappoint viewers with "hot spots," dim corners, or unreadable text, or you'll end up spending thousands to compensate by getting a new projector—which may only make the problems worse.

Projection Objections
For many churches that have never had a screen in their sanctuary before, the first hurdle is overcoming objections about installing a screen in the sanctuary. Some of the concerns involve experiences at other churches where projected images on the screen were washed out, too dark, or the print was too small. Members don't want the same problems in their church. Choosing to work with a qualified lighting professional minimizes or eliminates such problems.

"Don't just go shopping for a screen—get a professional," advises Manfred Freiberger of Stewart Filmscreen. Together, you and a lighting professional will be able to overcome the objections some of your parishioners might have to a screen in the sanctuary.

Perhaps the most common objection to installing a screen in the worship center is that it hides or covers some important element of the architecture or furnishings—a cross, altar, or stained glass window. Screen makers have many innovative designs that allow a screen to be retracted and remain out of view when not in use.

Someone in your church is sure to remind you that a projector and screen isn't needed because "we've never done it that way before." Gently remind them that the people you are trying to attract never knew life without television and they prefer and expect visual images to accompany what they are hearing. Since we can't eliminate television in our world, neither can we ignore those who grew up watching it. If the system under consideration will enhance evangelism among seekers, provide innovative education for members, or improve the quality of worship, then emphasize the screen's connection with current ministries of the congregation.

David Hull of The Screen Works sees their church customers using video systems to launch new ministries or improve existing presentations. New ministries include weekday movie-nights, community-building programs, after school programs, educational videos produced by inspired teachers, and presentation of budgets and treasurer's reports.

An understanding of the church's mission and the purpose of their video system is even more important than room measurements, says Dennis LaBissioniere of Harbinger Communications in Elgin, Illinois. And he says it isn't enough for a congregation to want a screen because others have one. The best way to overcome objections of reluctant members is to emphasize the mission of audio-visual equipment.

The Dynamic Duo
Although many churches buy a projector first and then the screen, the reverse order may be better. Think of buying priorities this way: which will most members see—the screen or the projector? While only the technically apt can understand the specifications and features of a projector, everyone knows when the screen is too small or the images too dull. The screen is where the medium meets the membership.

Pure reflection: the screen acts like a mirror in reflecting the projected image.

The projector is certainly the more expensive of the two parts of an audio-visual system. And you will need to know where the screen and projector will be located before purchasing either. While it is true that no matter how good the screen is, it cannot make a bad projector good, it is also true that even the best projector cannot overcome a mismatched or inadequate screen. Keep projector and screen as one purchase—well coordinated, balanced, compatible, and suitable.

A primary decision is whether to use a front or rear projection system. In many ways, rear projection is preferred and will generally offer higher quality images. However, the tradeoff is the necessity of space behind the screen, and control of ambient light between the projector and the screen. Many times, rear projection is just not feasible in a church setting. Jim Huttlebrink of Draper knows that to retrofit a worship area for a rear projection system is generally very difficult. That is why he suggests that lighting professionals be contacted early in the construction process to assure new buildings offer the widest range of options for an audio-visual system.

Ambient light is the amount of light in the room before the projector is turned on, and is an important factor in selecting both the projector and the screen. It's important to note how many windows the room has, which direction they face, and what kind of glass they have. A movie theatre has no windows and requires a different kind of screen than a church with several stained glass windows on the east wall of the sanctuary.

Keep in mind that projectors do not project a uniform brightness across the width of a screen, although some do a better job than others. Proper screen selection will help create the most uniform image brightness possible with the type of projector being used.

All About Angles
You might think that the purpose of a projector screen is to reflect an image projected on it, but that is not true. Replace the screen with a mirror, and you would have pure reflection. The reflected image would very nearly match the projected image in brightness and clarity. Unfortunately, there would be only one spot where the reflected image could be seen.

The real job of a projector screen is to impart the right amount of light scattering to the projected image so that the image can be seen from many different locations in the room. A Matte White screen surface is as close as you can get to perfect scattering. This surface makes the image on the screen visible from anywhere in front of the screen, and the image has uniform brightness regardless of the angle of the viewer from the screen.

Pure scattering: the image can be seen from any angle.

This type of screen would be used in a setting where a wide angle of viewing is necessary. Because the light is scattered in many directions, the brightness seen will be only a fraction of the brightness projected. Therefore, the projector must be powerful enough to overcome ambient light and create the appropriate brightness at any angle of viewing.

In many cases, a combination of reflection and scattering is useful. For example, when the projector is mounted overhead and shines down on the screen, some amount of reflection will direct more light energy to the viewers than will pure scattering. This type of screen is made by using a light-scattering coating over a reflective backing material. The density of the coating and the reflectivity of the backing determine the relative amount of scattering and reflection.

Another common situation is where the projector and viewers are both below the screen. Here, a screen that takes advantage of "refraction" is very useful. When light travels from one medium to another, it often changes direction. Glass has the ability to change light's direction, compared to light traveling through air. Screens are often covered with a layer of very small glass beads to provide refraction.

The end result is that some of the light is scattered, while some of the light is directed back in the direction from which it came. Again, the relative amounts of refraction and scattering are controlled by the construction of the screen.

Scattering and reflection

This brings us to the often-misunderstood concept of screen "gain." While gain is an important parameter in selecting a screen, a higher gain is not necessarily what you'll need. It may even be undesirable. Gain refers to the amount of light returned in the direction of the source when compared to a Matte White surface where the scattering is uniform. Matte White has a gain of one. The higher the gain, the brighter the image will appear, but in a narrower viewing range.

In the situation where the projector and viewer are on the same side of the screen, some degree of gain may help return more of the image brightness to the viewers rather than sending it off to the ceiling. Higher gain is useful when the viewing range is narrow, and there is a desire to get as much light energy as possible directed to those viewers. The same concept of gain applies to rear projection screens, except that the gain is achieved by allowing some light to pass directly through the screen in addition to being scattered.

Extend a line from the center of the screen, perpendicular to the screen's surface, to the rear of the sanctuary. Any viewers that are more than 50 degrees away from that line might find the image quality to be unacceptable due to reduced brightness and image distortion. That is why multiple screens at different angles or different positions may be needed when the room is very wide and a large number of seats are outside the screen's cone of vision. It is no wonder drama and music critics prefer sitting at "fifth-row-center" in many theaters and concert halls—it is the seat in the house that offers the brightest and least distorted image.

A Clear Resolution
Resolution is the ability to define small images. When projecting an image onto a surface, image resolution will be limited by the size of surface irregularities. Since a high-gain screen intentionally introduces irregularities by using glass or acrylic beads, resolution is affected. The compromise of a high-gain screen could be a loss of resolution.

Screen size is important when considering the resolution required. Obviously, a huge screen projecting large images and letters does not need the same resolution as a smaller screen. The important lesson here is to make sure that you don't pay for more resolution than what you really need.

What size screen is needed? The answer depends on sanctuary layout and the distance from the screen to the most distant viewer. It's also important that viewers not be too close to the screen.

Scattering and refraction.

Looking straight forward, we can comfortably take in a horizontal field of view of about 30 degrees. Any field greater than 30 degree causes discomfort after a short time of viewing. This sets a limit for how close viewers should be to a screen. The minimum viewing distance from the screen is about twice its width because at that distance the screen fills 28 degrees of the vision field.

The height of screen needed is easily determined by dividing the distance from the screen to the most distant viewer by eight. For example, if the farthest row to view the screen is 50 feet away, then an appropriate screen height is about six feet (50 divided by 8 equals 6.25 feet).

It's also helpful to know the size that displayed letters need to be for easy reading. To get this, convert the distance to the farthest viewer to inches and multiply by .0026. In our example, 50 feet equals 600 inches, times .0026 equals 1.56 inches. Letters should be displayed at about one-and-a-half inches high.

Ready to Buy
While technical characteristics are important, the simple reality is that the availability of money limits the kind of system your church will be able to purchase. You don't necessarily need the most expensive system to have an adequate and effective audio-visual component for your mission and ministry. "Every application requires a compromise of some sort," says Huttlebrink of Draper. Be prepared, knowing where you will compromise and where you won't. To keep the inevitable compromises minor, deal with a manufacturer or distributor who offers a large variety of screen surfaces and sizes.

Wendy Long of Da-Lite, a company that offers a broad variety of screens, says a manually operated, fixed screen costs between $150 and $950. Make that a motor driven screen and the price range expands to $1,000 to $4,000. To have an electric screen, the motor and concealed screen are usually installed on a wall or in the ceiling. The permanent installation of a rear projection screen, including the frame and mirror system, can cost up to $10,000, according to Long. On top of that is the cost of remodeling the space behind the screen.

Good viewing is limited to about 50 degrees either side of the projection axis.

One screen manufacturer, Vutec Corporation, has introduced a motorized screen that rises out of the floor when a wall or ceiling mount is not possible. According to Kirk Hammond, national sales manager, Vutec has obtained several patents for cutting edge screen technologies including the floor-recessed screen and high contrast/high gain screens. These innovations increase the options available to churches.

A portable screen represents another option for churches. Prices range from $700 to $1,500 depending mostly on size. A fixed frame, portable screen costs between $700 and $3,000.

Don't take a video projector screen purchase lightly. The information in this article should be enough to make you realize that there's more to it than getting the right size. Hire a lighting professional to help, and work with manufacturers that offer a wide range of products. Do these things, and you'll be sure to pass the "screen test."

John Stahlman (nonfictionwriter@msn.com) is a freelance writer living in Springfield, Illinois.