Digital fabrics

Projection screens are just as important part of an AV solution as the projector itself. But there are a myriad of factors out there which will influence your decision on which to specify.

Behind every good projector, is a good screen, as the old saying goes. Well it would do if the cliché writers were AV specialists. Whatever, you can choose the brightest, highest resolution projector you like for your customer, but if it’s not matched with an appropriate projection surface then it won’t perform to its full potential and more than likely the client won’t be happy.

More than that, a good choice of projection screen can actually help alleviate a number of the problems you can run into when specifying projection. High gain coatings can improve the brightness of an image, and glare from ambient light can be attenuated using a surface with high ambient light rejection.

For fixed installation there are a number of factors to consider with screen choice. Firstly there are fixed frame, or rolled screens. Within both of these there are options for front or rear projection although fixed screens tend to be more popular for the latter.

A fixed frame screen will give you the flattest possible image, due to the tension that can be introduced into the fabric, however clearly it’s not always possible or desirable to have a screen permanently in place. Projection screen fabrics tend to be sensitive to sunlight especially if made from vinyls such as PVC.

Rolled screens can be motorised, or manual, and the larger sizes can often be ordered with tensioned edges to produce a flatter projection surface. At the higher end of the price spectrum, there are now motorised screens, which are completely concealed from view when not in use – popular in high-end boardrooms or multipurpose venues.

A good example of this is the Integrator Electrol from Projecta. The company’s Marco Adriaans said: “A lot of companies spend a lot of money on designing beautiful boardrooms. But, in many cases, a screen is not a beautiful product. This is why we have developed this concealable product, and focused on making them easily integrated into the AV system.”

The Integrator Electrol can be controlled via RS-232 and Infrared, and has a clever flush fitting cover to conceal it when not in use. It’s currently available up to three metres in width, with the company working on a 4m version.

Other screens of this type are available from Draper. The firm’s Ultimate Access, Envoy and Ambassador ranges all feature close-able shutters, or finishes that can be covered to match the ceiling material.

Stewart Filmscreen’s Stealth Trapdoor is another possibility available up to 240cm wide normally or 250 using the company’s large ABT rollers. Unlike the other two, the Stewart model features a tabbed tensioning system, which the company calls Tab-Guy.

Screen type will also be dictated by the size of screen required. Rolled, top hung screens exert their own weight on the roller and therefore increasing screen widths require more and more heavy-duty support. The tension in the outside edges of the screen also causes them to bow inward leading to distorted projections. This can be solved with the addition of tabbed or tensioned screens - wire cables running along the outside edges of the screen alleviate the strain in the fabric and these are available from all the major manufacturers.

These are either used in larger sizes of screens, or in those for applications where a very flat image is important. Really large screens such as those over 5m wide require heavy-duty construction, and more powerful motors. Good examples are AV Stumpfl’s Magnum range, which can be up to 9m wide, and the Big Mot from Screen Line International, which is available in 16:9 format up to 10m wide.

Stewart Filmscreen’s Visionary Grande was announced at InfoComm 08, and is a size upgrade to its Visionary Electriscreen. The new model covers screen sizes from 10ft – 18ft (3m – 5.5m).

Projecta’s two large products are the GiantElectrol and GiantKing Electrol, which between them cater for images with sizes from 4.5m – 10m.

AV Stumpfl, also produces what it calls the Monobloc system. This is a modular, fixed frame solution, allowing the customer to build a temporary screen frame from aluminium structural elements. Stumpfl then supplies a screen of the appropriate size in any of the screen materials available. These are popular on exhibition booths and for corporate events. In this way, screens up to 7.50m x 5.69m in size can be assembled.

An alternative to tensioned screens comes in the shape of Projecta’s Matt White M fabric, this is

Aspect ratio is another key decision for screen choice. All the major manufacturers offer 1:1, 4:3 and 16:9 as off the shelf products, and most of them now have 16:10 versions of their integration products to cope with the advent of WUXGA type projectors in professional and business applications.

These days it is also not uncommon for more than one aspect ratio to be required. Normally this would have to be coped with by installing more than one screen, or the slightly undesirable method of shooting 16:9 content onto a 4:3 screen, leading to unattractive letter boxing in the projected image.

However, British manufacturer Harkness Screens has a solution, a double roller screen. This will feature two rollers in the same case, which means only one installation is required.

The choices listed above will be governed by the purpose of the installation, the size / shape of screen required, its budget, and the requirements of the customer. But on top of these there are also decisions to be made about the type of projection surface you need and the properties they give you.

There are a couple of key properties that need consideration. The first is Gain, which is a relative measure of the screen’s reflectivity. A screen with a gain of 1.0 reflects the same amount of light that arrives at the surface. Screens with higher gain values of 1.4 or even 2.0 focus the reflected light so that the screen appears brighter when viewed straight on. However this is achieved by sacrificing viewing angle and / or contrast in the image.

The viewing angle or cone means the same as it does when talking about any video display, but it is affected by the coating on the projection surface. When we talk about gain, it doesn’t mean that a screen is generating more brightness, it is simply focusing the available light in a smaller area.

Contrast is the ability of the surface to accurately reproduce and differentiate dark and light characters and backgrounds, or light and dark areas of a screen.

The most common surface type is a matt white. It’s the basis for all standard screens, with a gain value of 1.0 and uniform reflective properties. It also provides true-to-life colour reproduction. The downside is that it doesn’t cope too well with ambient light, requiring the room to be dim.

On top of this foundation, various coatings can then be added to, improve contrast or gain. Stewart Filmscreen’s UltraMatt range goes from 130-200, representing gains of 1.3 to 2.0. Harkness Hall runs a similar nomenclature with its Pearlux materials, which are available with gains up to 2.2

Projecta’s high gain or reflective range is called Datalux with options of gain from 1.5 – 2.2 The high gain comes at the expense of viewing angle, which is reduced to around 35 degrees off axis. The company also has a product called High Power, with a fixed, ultra high gain of 2.8, but the viewing angle here is reduced even further to 25 degrees off axis.

The other main type of surface available is high contrast. These are grey coloured materials, which improve the appearance of blacks in a projected image. As the gain of these screens generally means they need to be used in low lighting conditions – they don’t cope well with sunlight or other sources interfering. Projecta’s High Contrast material has gains in the range 0.8 – 1.0, which is comparable with Draper’s HiDef Grey and High Contrast Grey screens.

Stewart Filmscreen produce a number of grey surfaces. GrayHawk G3 is optimised for use with high definition projectors with a gain of 0.92. GrayMatte 70 is a much lower gain material designed for use in edge blending applications or in curved / circular projections.

Rear projection materials are also know as diffusive reflective fabrics. Light is transmitted by the screen and diffused as it passes through. These are more commonly used in fixed screens, although retractable screens are also available. Rear projection materials are limited in their gain values to 1.0 as they cannot increase the amount of light they transmit beyond what hits them!

StarGlas from Stewart Filmscreen is one such fixed material with some pretty impressive capabilities. It qualifies as safety glass meaning that it can be used in some construction situations, or as a table surface.

Films can also be applied to glass or Perspex surfaces to make them suitable for rear projection. This has proven extremely popular in retail applications. They started as a fairly expensive option but companies such as Harkness have released new products lowering the cost.

Finally it is possible to perforate certain projection materials. This allows them to transmit sound, and means that audio components can be installed behind a screen. This has interesting applications in digital signage, and also in settings where a rear projection solution has been installed. If carefully integrated, all the AV equipment can be concealed behind a screen!

As with projector choice, there is no cookie cutter answer to what the right selection is. All of the screen manufacturers mentioned here will create a bespoke combination of screen material, mounting options and screen shape / size depending on the situation.

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