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WP: Silver 5D

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FAQ's


 


Why Silver 5D?

The preservation of a polarized state of projected light into discreet information streams for each eye is a cornerstone of many 3D displays. The polarized nature of the projected light is oriented so that each eye ignores the content intended for the other eye via the simple phenomenon of crossed polarizing filters. There are of course other regimens for delivering 3D but we focus on "passive polarized" systems for this discussion.

Providing a "Silver" screen designed to deliver polarized light minimally altered, has been part of Stewart Filmscreen Corporation's business activity since the earliest days of the company in the fifties. The "silver" screen would preserve the state of polarization delivered by synchronized projectors, and since the screen was high gain, it would make up for the insertion losses of the projector mounted filters, and the corresponding filters in the glasses.

The Problem

Silver screens designed to preserve the polarized state of light projected upon them, have super high gain factors, very narrow viewing cones, and as a result, perform poorly in most measurable qualities valued in projection screen applications. Insertion loss, an inevitable aspect of the implementation of any 3D regimen, results in very low light levels coming off the screen. If a venue is also used for 2D projection, without filters and glasses, the silver screen is revealed to be plagued with a distracting hot spot, inferior center to edge uniformity, and excessive color shift particularly when viewed even slightly off axis.

Why Does this Happen?

As 3D has been refined over the years, the Silver screen has been a boon, but also a weakness of these displays, because of the compromises that need to be made to preserve polarization. Legacy technology silver screens tend to have metrics which are somewhat similar. The make-or-break metric for a silver screen is the extinction ratio. This metric provides a contrast ratio between the maximum light passable through filter and glasses in the open condition, divided by the lowest amount of light passed by the same filter regimen in the "closed" condition. A high performance silver screen can hold two channels of information discreet at the ratio of 250:1 using quality linear polarizing filters. Circular polarization ratios tend to yield a bit lower, due to the quarter wave baseline component, but they are much more forgiving for head movement from side to side.

The unfortunate side effect of a high ratio of extinction is a real narrow viewing cone. A quality matte fabric made to deliver perfect white field with optimum center to edge performance will have a viewing cone of at least 85 degrees, Stewart Filmscreen Corp makes this and many other high performance matte types with elevated gains, and tailored off axis behavior, with viewing cones well over 65 degrees. They fall flat with polarized light. To this point, a screen with excellent ratio of extinction usually has a viewing cone between 14 and 24 degrees, and typically very high gain, 3.0 to 4.0 and distinct hot spot behavior under projection.

Most commercial cinema projection is designed at fairly long throws 3:1, 5:1 and higher in big houses. The long throw can help disguise the silver screen's flaws, since long throw projection delivers light at a more orthogonal distribution than a short throw system. Home cinema and post production screening rooms are often built with much shorter throws. In these sorts of setups, the typical silver screen shows a pronounced hot spot and the expected lack of center to edge uniformity and color shift common to many high gain screens. When you display 3D, the depth effect does mask the hotspot and fall off pretty well until a well lit high key shot comes along and reveals problems. If you attempt to show high definition 2D material on such a screen, you immediately become aware of the planar surface of the screen, the unkind and inaccurate colorimetric tendencies, and the solarizing beam splitting treatment of white fields. In the world of commercial cinema, the proliferation of 3D content has been extensive, with many features competing for a limited, but expanding amount of 3D capable theatres. In home cinema, the market penetration of 3D content is not as extensive, and few viewers have purpose built venues for 2D and 3D. A single home cinema is available and usually there is one screen. Typical silver screens are very far from the performance of reference quality for 2D and many rooms just cannot accommodate a two screen solution, and are too short in throw to work correctly with Silver screens. Parabolic screen surfaces are offered but they do not co-exist with proper masking systems and offer sub par performance for both formats. The silver screen is problematic in home cinema.

The Basic Solution

So what if you could cut that problematic behavior in half? One of Stewart Filmscreen's core customer groups is post production, color timing and Q.C. suites operated near our Los Angeles area headquarters. These customers are heavily involved in stereography, and the silver screen is front and center before some highly critical eyes. Conventional silver screens can be fatiguing, and the consensus request is for us to reduce hot spotting and improve center to edge uniformity, however possible. Lowering the gain of a silver screen seems like an easy answer. The challenge, however, is that when you lower the gain of the screen, the crucial ratio of extinction plummets disproportionately. Insufficient ratio of extinction results in ghosting, and often times a grain to the appearance of the screen. When the tipping point of functionality is reached, the screen may present an image which resembles the fog of analog static interference. None of these behaviors is acceptable in a screen. If you can lower the gain, naturally, the viewing cone will widen and the screen will start behaving more like a normal screen, better center to edge uniformity, less hot spotting. The upside of this possibility was too enticing for Stewart's engineers and chemists to ignore. So we got to work to really explore how to lower the gain of a silver screen without crashing the critical ratio of extinction. This is the premise and delivery of Stewart's Silver 5D fabric.

Stewart Silver 5D

Stewart's R&D team has spent several years quantifying, re-formulating, refining and prototyping new ways of producing silver projection surfaces. No stone has been left unturned, from the method and formulation of the substrate, to the formulation and application of the optical coating. Stewart's team crafted many hundreds of sample formulations, exploring the function and nature of the ratio of extinction, how it works on a microscopic scale. Theories were tested and verified under projection. Stewart did the work necessary to really understand how each change in formulation and each trend in the metrics, affects all measureable and observable behaviors of the surface. We learned a lot and we're re-defining what can be done with a polarization preserving screen. Silver 5D has significantly wider viewing cone than ever achieved by a Silver screen, 30 degrees plus, providing much improved center to edge uniformity. The fabric has significantly lower gain, 2.0 and yet furnishes a robust ratio of extinction, 140:1, more than adequate to furnish ghost free images. The net effect is a much more uniform 3D presentation for shorter throw displays, and a very nice high contrast 2D screen, that's more in scale with the 3D in terms of overall illumination. The screen is not a matte white screen, but with some calibration and a medium throw design, you will be surprised at how vivid and watchable the image will be. Stewart Silver 5D is available micro-perforated, and in all of Stewart's mounting systems for front projection application. Any electrically operated screen option, or any fixed frame option from basic frames to fully automated digitally operated memory equipped masking systems. Thank you for taking the time to read this article. We suggest a Stewart 5D Silver screen for your next stereoscopic theater project, and stand ready to help you at (800)762-4999.

 
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