The Perils of 16:9 Rear Projection in the Real World
By Will Craig
Multimedia Systems Consultant
Elert & Associates
A university medical school hired an architect to design the renovation of a historic Art-Deco auditorium that has served the institution for 50 years but has fallen on hard times due to wear-and-tear and neglect. The original architectural pre-design called for the latest and greatest state-of-the-art technology, but unplanned abatement and construction cost overruns forced the university to be cost-conscious in selecting their technology. Nevertheless, everyone has to have their say. The user groups requested that the system be highest-possible resolution. The architects requested that the system have as high a brightness as possible. Everyone agreed that both the screen and the projection system needed to have a 16:9 native aspect ratio.
The consultant dreamed of specifying a Barco iCon H600 or a Sanyo PLV-HD10, each offering 1920x1080 native resolution and greater than 5500 ANSI lumens brightness. However, the high cost of these projectors (around $50K each) and the desire of the University to standardize (meaning that it would be cost-prohibitive to put these in other rooms, even if the budget supported them for this particular project) overruled the consultant’s initial ambitions.
The second plan was to step down to 1366x768 WXGA projectors, double-stacking a pair of Panasonic PT-DW7000UK projectors (6000 ANSI 3-chip DLP). At this brightness, the projectors could be run at the reduced light output level, providing an 8,000 ANSI image with long-life lamps. At around $25K each, the university balked at the price and also was concerned with the lamp replacement implications of four bulbs burning at a replacement cost of over $1200/pair.
The third plan was to go in on the low end, with double-stacking a pair of 3000-ANSI Sanyo PLV-80 projectors (around $10K each, $20K for two). The advantage of double-stacking is that if one projector or lamp fails, then the other will still provide an image, even though it will be half as bright as the two projectors. This is especially important with this model of projector, as it has only the single lamp – good news for the lamp replacement budget, bad news if the lamp g'es out just before a major event or lecture and you don’t have a contingency plan (such as a double-stack arrangement).
Then the screen and mirror manufacturers weighed in with the physical space constraints. The installation of double-stacked projectors requires careful alignment of the two images on the vertical plane. With most mid- to high-level projectors, this is possible through the vertical lens shift feature. However, the ultra-wide-angle lenses that are required to fill a rear projection screen from a short distance (typically .8:1.0 throw:width ratio) are generally not capable of being used with a lens shift, making them unavailable for multiple-stack installations. The next larger throw ratio, 1.2:1.0, required the second mirror in the projection room to be larger than what the screen and mirror manufacturers could fabricate.
They provided two suggestions: reduce the screen size, or go to a side-by-side edge-blending scenario. The architect and consultant immediately recommended against reducing the screen size – the auditorium is historic and the available screen size was already limited by the proscenium opening, which could not be modified. Reducing the screen size even further would dramatically reduce the useful capacity of the room for the graphics-intensive curriculum activities planned for the space.
In edge-blending, two typically non-16:9 projectors are placed side-by-side and spaced so that each fills half the screen, with the line at which the two images meet being digitally blended so that (in theory) it is not apparent to the audience that the image is coming from two projectors. When comparing this approach with the University’s project priorities, namely having a contingency plan for projector failure at the worst moment, this approach fell short. If either projector or lamp fails, there’s only half an image on the screen, which is not useful. The other problem with this approach is budget: the rear projection mirror assemblies cost almost as much as the projectors themselves. With the edge-blending strategy, the project pays for not one but two separate mirror assemblies (albeit slightly smaller ones), making this solution not-especially-budget-friendly.
The final decision was made by the project manager to balance these competing priorities of budget, performance, and reliability. A single Panasonic PT-DW7000UK projector was selected, with a .8:1.0 ratio lens and set at full brightness (6000 ANSI). This compares favorably with the performance of the edge-blending solution. Budget-wise this configuration is half the cost of the double-stack, half-power configuration of this model (if it were possible given the limitations of lensing and mirrors). The downside is higher cost-of-ownership given the 1500-hour life expectancy of the lamps and their relatively high replacement cost.
The lesson? Don’t get too hung up on a single solution. In the world of audiovisual systems, there are usually several solutions available, each with their own advantages and pitfalls. And, whenever possible, learn from other people’s experiences.
Will Craig CTS-D, CSI is a multimedia systems consultant with Elert & Associates, a nationwide technology consulting firm specializing in working with higher education and K-12 clients.