If you wandered the LDI show floor, looking at various pattern projectors — ellipsoidal reflector spotlights, automated spots, and effects projectors — did you consider how you might describe the clarity of their projected images? Is it the sharpness of the edges in the images that makes the difference between those that are sharp and those that are fuzzy? Or is it how dark the black areas are in contrast to the light areas that make the big difference between images that are clear and those that are murky? Perhaps it's a combination of both that sets apart the really good image projectors from the not-so-good. After you have found a luminaire that seems to be the best at projecting a clean, sharp image, how do you tell someone else about it? Did you bring a colleague over to see your “best” choice at LDI, and did he take you over to the other side of the hall to see his choice?
This is a problem Mike Wood (Mike Wood Consulting LLC) has been grappling with as part of his work as a consultant and product reviewer: How do you tell someone, when you can't show him, how good a luminaire is at projecting clear, sharp images? There are ways of measuring and describing the performance of high-quality projection lenses, but these methods don't work well with the lens commonly used in theatrical luminaires. The lenses used in them aren't as good as projection lenses, so using projection lens measurement techniques is a bit like measuring the size of a bedroom with a micrometer. We need something simple, like a yardstick, to do the job. Wood has developed one such “measuring” device that looks like it will work. It's a method that compares the contrast ratios of a projected coarse-grid gobo and a fine-grid gobo. It's broadly applicable to many different types of luminaires, so it would be handy to have it as a standard. The Photometric Working Group, part of ESTA's Technical Standards Program, has started a project to turn the method into a standard that anyone can use. The project is called BSR E1.35, Standard for Lens Quality Measurements for Pattern Projecting Luminaires Intended for Entertainment Use. Look for forthcoming public reviews of the draft standard; input from the public will be needed to make sure that the standard is clearly written and that the method addresses the needs of the industry.