February 2009
In this issue:
Maximizing Your AV Budget
Product Spotlight - Mediasite
Tech Tip - Front vs. Rear Projection
News Bites
Return to Main Newsletter
Scott Collinsworth
Director of Sales
Rental and Staging
Image Audiovisuals, Inc.
2130 S. Dahlia Street
Denver, CO 80222
303-758-1818
www.imageav.com
http://imageavblog.com
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Tech Tip - Front vs. Rear Projection
This month, Image Audiovisuals answers a question that many meeting planners have when planning for AV with their events: Which is better, front or rear projection?
First, a quick overview…
Front projection systems consist of a matt-white screen with a projector situated on the audience, or front side of the screen.
Rear projection systems consist of a grey, translucent screen with a projector situated behind the screen and hidden from the audience’s view.
Let’s discuss the advantages and disadvantages of both of these screen types:
Front projection screens are reflective, so they “bounce” the projected image off of the screen surface and back in all directions to the audience. Front screen material typically has a gain of at least 1.0, meaning that all of the light reaching the surface is reflected back to the audience, allowing very efficient utilization of the projector’s brightness. Front screens also have a very wide viewing cone, allowing audience members seated to the sides of the screen to still see the same quality of image that those seated directly in front of the screen see. Unfortunately, all that reflectivity a front screen offers comes with some caveats. Along with the projected image, ambient light also gets reflected back to the audience. House lights and stage wash fixtures casting light on the screen surface can reduce contrast and “wash out” the projected image. Front screen set-ups typically take less of a footprint than rear screen sets do, but the projector in a front screen environment is in plain view of the audience, and great care should be taken so that the power and signal cables feeding the projector are well secured to eliminate trip hazards. Also keep in mind that audience, venue staff and others who walk between the projector and screen will cast shadows of the screen, disrupting the quality of your presentation. Front projectors can be rigged, or “flown” from the ceiling in certain venues to eliminate some of these issues, but this can add significant expense to your production.
Rear projection screens are transmissive, meaning the projected image passes though the screen to be viewed by the audience. Rear projection screens have an uneven gain structure; it’s over 2.0 when viewed on-axis, or directly in front of the screen, but drops to under 0.5 when viewed at an angle of 50 degrees off-center. Careful planning is in order if you plan to use rear projection screens in wide rooms where the viewing “cone” is greater than 90 degrees, because of the brightness falloff of the projected image. Rear projection screens reject ambient light from the audience side of the screen surface, so they are a great choice for higher brightness environments, provided that the ambient light is controlled on the projector-side of the screen. With the addition of screen dress kits which “frame” the screen with fabric panels and velour pipe and drape, rear projection set-ups allow you to create a very professional and polished look to the front of your room. The projector, stand and all of the cables are not visible to the audience, and there are no issues with people walking through the projected image and casting shadows on the screen. Rear screen projection needs more space in the room, sometimes moving the “front” of the room 20 to 30 feet out from the front wall, depending on screen width and projection lenses used.
The key to insuring that you have made the proper choice is careful planning.
Ask your AV company to help determine what factors to be aware of, and if you have the space necessary for either screen type.
A room diagram will insure that you have room for seating, food and beverage and, of course, the audio visual equipment necessary to project your message!