Projection Screens

Technical Information

Projection Methods | Using Screens Outdoors | Screen as Cyclorama
Minimizing Bounce Light | FAQ

Projection Methods

FRONT PROJECTION

Front projection is the use of a source to bounce an image off a surface and back to the viewer. In this case, the surface should be highly reflective, in order for the audience to get the brightest image possible. "On equal-intensity, distance, and size-of-image bases a front projection is brighter than a corresponding rear projection. In short, it takes less wattage to project the same image from the front than from the rear". The source is normally hidden from the audience, but must be placed with a clear throw to the surface. If the throw is very long, a source with the appropriate wattage should be chosen.

This method is best for situations where the source is not very strong, as a highly reflective surface will maximize the amount of light being bounced back at the user. A front projected image maintains its intensity, clarity, and contrast through a wide angle of vision, meaning those sitting house right and left can see the image almost as well as those in the center of the audience.

Using a front projection surface has some disadvantages, however. First, having a very light colored surface on the stage can be distracting. Some designers feel their audiences are left "waiting for the movie to start". The bright surface also reflects ambient or "bounce" light back to the viewer, which can cause the image to look washed out if care is not taken in lighting the areas adjacent to the surface. Backlighting and side lighting actors and scenery becomes very important in this situation in order to keep the actors shadow off of the surface. Hiding the source in an extreme lighting position to avoid casting shadows can cause distortion in the image and requires correction in the slide to compensate.

REAR PROJECTION

Rear projection is the use of the source to transmit the image through a screen to the viewer. In this case, the surface should transmit an image with true optical clarity and brightness. A higher intensity source is necessary as the light rays are forced through the surface to the viewer. By definition the source is masked to the audience, but space must be left backstage between the source and the surface, in order to prevent the actors and crew from casting shadows on the surface. The darker colors included in the rear projection palette allow the

surface to blend inconspicuously into the scenery. Actors can stand in front of the screen without blocking the image. Because the image is usually projected on an angle directly perpendicular to the surface, distortion is generally not a problem. If the surface is painted, varied and interesting effects can be achieved by projecting them from behind so that they blend with the painted picture. Day to night effects are a perfect example of this.

Rear projection also has its disadvantages. In order to allow the image to pass through it, and because the viewer is usually looking almost directly at the source through the screen, a bright spot ("hot spot") is often visible at the center of rear projected images. Because of the density of the material required to diffuse the image and prevent hot spoiling, the image quality falls off sharply when the viewer is seated outside the 60 to 110 degree viewing cone. The actual size of the viewing cone is dependent on the color of the surface chosen, with darker (and therefore denser) surfaces "falling off" fairly close to the center axis.

Using Screens Outdoors

1. Exposure to UV rays will break down any vinyl product over time. Rosco screens can be expected to stand up to UV exposure for about 3 years, depending on conditions.
2. Extreme cold will cause the vinyl to freeze. The screen should be allowed to come to room temperature before its is handled, or the screen will crack.
3. Provisions must be made for wind speed, such as perforations, scalloping, strong supporting structures, or break away tie downs.
4. Water will not affect the screen as long as any residues and/or cleaning chemicals are removed promptly and completely.

Using Screen as a Cyclorama

Twin white screen is an excellent cyclorama for film, video, and theatre. The milky white color diffuses light exceptionally well, with no scalloping to give away lighting instruments. Beautiful, infinitely varied effects can be achieved by front lighting from the ground row and rear lighting from the top. Instruments can also be hidden from view by a vinyl cyc, eliminating the need for masking, or by breasting the screen forward 5 degrees. Vinyl screens are durable, easy to care for, and can be made up to 200 feet high, with no practical limit on width. Once a mark gets on a muslin cyc, there is little to be done except spot cleaning. Vinyl screens can be wiped clean with mild detergent, and can be rolled on a batten for permanent storage.

Tips on Minimizing Bound Light (Ambient Light)

1. Rear-screen projection is less affected by ambient light than front-screen projection, so work with rear-screen techniques whenever possible.
2. All Rosco screens have a matte front to deflect ambient light.
3. Deaden the reflective quality of the floor by using Rosco Tough Prime Black, or Supersaturated Black mixed with Rosco Clear Flat as a sealer.
4. Hang a seamless black scrim at least 2" in front of the screen. The scrim will absorb the light without affecting image quality.
5. Adjust the image or the screen to two feet or more above the stage floor so that bounce light is reflected below the screen.
6. Make sure lighting instruments in the vicinity of the screen are angled to reduce light being thrown directly on the screen.
7. Use high-hats and barn doors to focus light off of or around the screen.
8. Have the actors maintain a "neutral zone" at four feet from the screen so that lighting them with backlight and sidelight is easier.
9. Maximize the brightness of the image by using high contrast imagery when working with projection materials. Keep the image size as small as possible, and use the proper focal length lens. Keep the projector as close to the screen as possible.

FAQ

Q. I need a screen with the widest possible viewing angle; which screen material should I use?

If you are doing rear projections your best choice is twin white for a wide viewing cone. If you need a front projection screen choose front white for wide viewing.

Q. I want to do front and rear projections; which screen should I choose?

Twin white is the screen of choice if you need to do both front and rear projections. You may also use grey screen if you want the projection surface to blend into your scenic elements.

Q. Can I use screen as a bounce drop?

Yes. Light translucent and front white are excellent choices for bounce drops. Twin white will also do a good job.

Q. What is the "standard" edge finish on a custom screen?

"Standard" finish is grommets on 12" centers on the top edge with a pipe pocket on the bottom.

Q. What options do I have for edge finishing on my custom screen?

You have many options ranging from no finish to velcro to snaps to grommets all around. Contact our sales department for full details.

Q. Can I have custom screens made in different shapes?

Yes. We will manufacture screens in any shape. Please call us for pricing.

Q. How can I get the wrinkles out of my custom screen?

Upon receipt of your screen; bring to room temperature and hang immediately. The wrinkles should disappear within a day or two. If you have very stubborn wrinkles turn the stage lights on to warm the screen up a bit, this will speed the process. Please note: We do not recommend the use of heat guns on screens for wrinkle removal as the intense, concentrated heat may damage the screen.

Information courtesy of Rosco.