Tel: 905–690–4709 dk@tfwm.com - Darryl Kirkland, Publisher

Screening Imperfections

Church audio/video design offers many challenges in today’s not-so-perfect world of light and hard surfaces of Houses of Worship. We all love the very high cathedral ceilings and the wonderfully inspiring stained glass windows, along with plenty of light. Isn’t it nice to have bright white paint on all the walls and a very wide sanctuary creating a sense of spaciousness?

The above are all important features for a church that is comfortable and open. However, high cathedral ceilings make it difficult to hang an electric projection screen. Those wonderfully inspiring stained glass windows let in a great deal of light (granted, colored light but still light), which along with the bright white walls are harsh on a projected image. Viewing angles for those on the outskirts of the congregation area work against the laws of physics, because a projected image is less bright at extreme angles.

This article is designed to help you understand how to overcome these challenges by choosing the right screen, and two-piece front and rear-projection systems to help get the message to your church body.

SOURCE, ENGINE, DISTRIBUTION
Your church’s visual system can be thought of much in the same way as the sound system. First, your audio system has a source (CD player, Microphones, etc.). That source is then processed through an engine (an audio amp and mixing board), is then sent for distribution (through your speaker system, stage monitors, etc.).

Your visual system has much the same type of distribution path. It has a source (such as a video camera, PC or Mac presentation, or DVD). The projector serves as the engine, and the distribution is the projection screen; a crucial part of the video chain, and the one thing the audience actually ends up viewing.

With all quality audio/visual projects, each component must be of excellent design to give a first-rate presentation to your sanctuary. If you wish to have high quality sound, for example, the last thing you would want to do is buy and install low-end speakers with high-end components. You’d end up with less than inspiring audio.

The same holds true for the video system. In the video realm, high quality means high horse power (ANSI lumens) projectors and high-quality projection screens. It is a known fact that the projection screen is 50 percent of a two-piece visual system, viewed 100 percent of the time during worship. Buying a top-of-the-line projector and skimping on the screen is the same as buying top-of-the-line audio components and chintzy speakers.

AMBIENT LIGHT
Let’s take a look at some of the ways we can maximize our visual presentation in the sanctuary. Ambient light (anything from natural light coming through a stained-glass window to chandeliers) washes out screen image contrast, destroying the contrast between white and dark parts of the image. The worst-case scenario for ambient light is light from untreated windows coming from directly behind the congregation. Slightly less offensive, but still very undesirable is to have ambient light close to and above the screen, with light flooding the screen surface. If you must have some ambient light–and certainly less is better–then it is ‘best’ to have it come from the left or right side of the congregation.

However, there are ways to combat ambient light issues. One solution is to purchase a high contrast Neutral Density Gray Screen with optical coating. A neutral density gray screen makes blacks blacker and therefore improves contrast. Also important is the right video projector with 4000 ANSI lumens or higher depending on image size (larger image sizes need higher lumen projectors). Another key consideration is ambient light direction related to the Neutral Density Gray screen location and the direction of the ambient light.

To illustrate this concept, let’s take this one step further and relate Lumen output from a video projector to what your eyes actually see reflected off the screen surface. The projector output, as I stated earlier, is measured in ANSI lumens and the light that is reflected to your eyes is measured in Foot Lamberts. The image on all projection screens always measures a higher Foot Lambert reading in the very center. A commercial theater screen, at best, has a Foot Lambert reading in the center of around 14 to 16 Foot Lamberts (in a darkened theatre depending on age and wattage output of the projector lamp). An easy way to calculate image brightness on your sanctuary screen is with the following formula:

Image Brightness Calculation

Projector Lumens ÷ Projection Screen Square Footage = Y

Y x Screen Gain (reflectance optical quality of the screen material) = Foot Lamberts

Example:

Screen: 0.92 Gain Neutral Density Gray Screen

Screen Image Size: 9′ x 12′ = 108 Sq Ft.

Calculation:

4,000 Lumen Projector ÷ 108 Sq. Ft. = 37.03

37.03 x 0.92 Screen Gain = 34.06 Foot Lamberts

If you want to maintain a brighter sanctuary when projecting an image, then you need a very bright projector (8,000 to 10,000 ANSI lumens or more) and a high contrast neutral density gray projection screen. Again, ambient light control near and around the screens when projecting an image is the best solution to this ever-present problem. The lower the room’s ambient light, the better the image quality will be.

Peak Brightness and Projection Screen Gain
Front Projection Reflective Gain

Most Front Projection screens used in churches today are Angular Reflective. This term relates to the angle of light coming from the projector (projector location related to the screen surface location). On an angular reflective screen, light coming from the projector makes contact with the projection screen at the same angle that the light reflects off the screen. In other words, if the projector is located in the upper third of the image plane then the angle from the lens to the center of the screen may be around 15 degrees. The light rays from the screen will reflect at that same 15 degrees to your congregation. Those seated in the center of the sanctuary will be receiving the maximum amount of Foot Lamberts (Peak Brightness/Gain). Everyone to the left and right of center have a slightly less bright image depending on their angle of view (seat location) and the reflective quality of the front projection screen material used. There are different screen materials for different applications.

Rear Projection Translucency Gain

Most Rear Projection screens used in churches today are of the Rigid Diffusion type. The thickness of the acrylic or glass depends on the size of the screen. Larger sizes require thicker glass or acrylic to maintain their rigidity. The optical diffusion coating is laminated either between two pieces of glass or laminated on the viewing side of acrylic or glass. This diffusion coated glass or acrylic comes in several translucency gains, as well as color tints for enhanced image contrast.

Rear Projection Screen Technology
Rear Projection is popular in larger Houses of Worship (usually 750 seats or more). Rear projection can be a very effective way to combat ambient light as it is more forgiving— it maintains a high contrast, assuming you have the right screen and projector combination. Another benefit of using rear projection is that the issue of dropping a screen from a high cathedral ceiling is rendered moot. Screens can be enclosed on either side of the stage, six to eight feet above the floor height, depending on sanctuary layout and size.

With a rear projection system, first surface mirrors (either glass or Mylar) can be use to “fold” the image to save space behind the screen. Folding the image with either one or two mirrors (depending on space availability behind the image) works well, assuming you purchase a projector with enough power (ANSI lumens) to still have a bright image on the screen. Again, the bigger the rear-projection image the more output is needed from your projector.

Most rear screens for the church environment are of the Rigid Diffusion type (Acrylic or Glass) and are coated with a dark gray translucent film to enhance the image black levels for higher contrast presentations. One new product for the rear projection screen market (called StarGlas) allows the optical film to be placed between two sheets of tempered class (tempered for safety reasons) and tinted to reject ambient light.

Rigid Rear projection keeps the image stable, and your projector doesn’t have to hang out in the middle of the sanctuary, detracting from the beauty of the architecture.

Another way to do rear projection (and front projection for that matter) in a House of Worship is with a “lift” rear projection screen that comes up either out of the stage or out of a roll-around case. This is an excellent solution for saving space and cost when only one center rear screen and projector are needed to present the message. This screen can be raised and lowered (electrically) at will during the service. Screens such as this are hugely beneficial for the aesthetics of the sanctuary. Screens can be out of sight when not in use, leaving religious art and icons, as well as the architecture and spirituality of the structure as the main attraction.

DETERMINING SCREEN SIZE
The “Art” of determining screen size is somewhat based on personal preference. However, you need to be cognizant of the following:

1) Distance from back row of seats to screen surface.

2) Shape of the sanctuary, (shoebox shape or not too deep but very wide)

3) Special considerations for sanctuaries with balconies.

4) Flat floor vs. a floor that slopes to the front.

5) One, two or three projector/screen combinations.

6) Lens throw distance needed from projector to screen.

7) Font size desired for Bible verses and words to songs presentations.

8) Ceiling height considerations (how high is the screen case mounted).

9) Screen size (does a larger screen block the view of the Cross, stain glass window, etc.?)

10) Projector location related to image size.

Taking all the above into consideration the general “rule of thumb” for calculating image size related to viewing distance is as follows:

Image Size Calculation

1/6 the distance from the desired screen location to the last row of seats

Example:

Let’s say this distance is 60 feet. The screen height should be 1/6 that distance (recommended for data projection) or a 10’ high image. If the desired aspect ratio is 4:3

(1.33:1 NTSC format) then the image size will be 10’ high by 13’ 4” wide. If the desired aspect is 16:9 ( 1.78 :1 HDTV format) then the image size will be 10’ high by 17’ 9 1/4” wide. The most common aspect ratio used in churches today is still 1.33:1 as almost all source material available is in 4:3 (NTSC) format. I know of some churches that are preparing for the future by purchasing 16:9 (HDTV) screens even though their source material is not in High Definition format. Using a 16:9-formatted screen while the existing source material is 4:3 means that both the left and right sides of the image will remain dark when under projection.

Looking at the format example above the difference in image width between the 4:3 and 16:9 aspect ratios is that the 16:9 ratio is 4’ 5 _” wider or 2’ 2 5/8” larger on each side of the 4:3 aspect image. Therefore the dark part of the screen image would be over 2’2” on each side of the image when projecting 4:3 format (133:1).

The goal of every technology minister and church audio visual leader should be to push the envelope and achieve the best quality presentation. Using the right combination of quality components is something to strive for, to be the best we can be in this less than perfect world.