FEATURE: PROJECTORS
Time to focus on lenses
Twenty-three Optoma EX875 projectors with short throw lenses and off-axis capabilities were used in an underground exhibition commemorating Dunkirk
In recent years, the excitement in the projector world in any discussion of image quality has been about increasing resolution, higher brightness and improved contrast. The focus of attention has been on the light modulator and the illumination source. Ian McMurray looks to redress the balance
[KEY POINTS]
IT’S BEEN very easy to overlook the fact that, without appropriate lens technology, many advances in projection would not have been possible. Beyond this, the new ways in which projectors can be deployed – helping projection to continue to remain relevant in applications that would otherwise perhaps have fallen under the spell of fl atpanels – have been largely a function of lens technology.
RESOLUTION DRIVES DEVELOPMENT “Projection lenses have been continuously developed to meet the requirements of increased resolution with smaller pixel DMDs,” notes Mark Wadsworth, international marketing manager at Digital Projection, “and increased angular coverage and depth of fi eld for wide-angle installation such as domes. Image fi elds have been increased to allow greater off set, and complex apertures included to increase contrast by taking advantage of the asymmetric illumination characteristics of DMDs.” Richard Marples, strategic
marketing director, venues and attractions at Barco, has noted a similar phenomenon in relation to DLP. “The main developments
26 June 2014
Higher resolutions have driven the design of new lenses that can do justice to the increased pixel count
in the last year or two have been the increases in resolution and the subsequent changes in lens that it has needed,” he says. “With the DLP pixels getting smaller and more numerous, we have needed to introduce new lenses that can cope with this.”
Short throw – and especially ultra-short throw – lenses are hot, and allowing new applications for projectors
“Lenses, of course, had to
follow the developments in resolution,” adds Hartmut Kulessa, marketing manager, projector products at Panasonic. “With the widespread adoption of WUXGA resolution, we upgraded our lens range with lenses that can cope with the detail and crispness of high- defi nition images.” Few would doubt the
contribution the lens makes to projected image quality – but to what extent is that task shared with the sophisticated image processing technology now found, to a greater or lesser extent, in modern projectors?
‘In order to
project perfect images you need both
excellent image processing and very high- quality lenses’ Richard Marples, Barco
IMAGE QUALITY: IT’S ABOUT THE LENS – MOSTLY “Lenses and image processing go hand in hand,” avers Kulessa. “Without a precise and uniform physical focus right on the surface of the screen, the best signal processing won’t work any magic in improving the picture quality. Signal processing, of course, is very powerful when it comes to enhancing the original source content with frame interpolation for better motion sharpness
Both image processing and lens design contribute to image quality – but of the two, the lens is the more signifi cant
or frequency dependant sharpness control.” “Perceived detail and motion artefacts, such as frame judder and smearing, are down to image processing,” says Justin Halls, head of product marketing at Optoma. “The quality of lens impacts upon pixel sharpness. The better the lens, the clearer the image will be. Optoma recently launched the HD91 LED home cinema projector. In home cinema, viewers sit relatively closer to the screen than they would in a typical conference room or lecture theatre, so excellent quality optics are vital for picture quality.” “The projection lens essentially relays the illuminated static DMD source onto the screen,” notes Wadsworth. “The ‘photographic’ quality of the image – distortion, pixel blur or sharpness, chromatic shifts and so on – will depend on the quality of the projection lens. Misaligned DMD optical systems can produce registration errors of the DMD in three chip systems, and the electronics can produce motion and greyscale artefacts in the
Most lens designs are a compromise between functionality, image quality and cost. The fewer the compromises, the higher the price
image. The overall visual experience will depend on eliminating errors in all these areas.” “In order to project perfect
images you need both excellent image processing and very high-quality lenses,” agrees Marples. “It’s no use having one without the other. Artefacts produced in the processing will not be hidden by a good lens, and a bad lens will always look bad, regardless of how good the processing is.” Vivitek’s director of EMEA
operations James Hsu is in no doubt. “A good lens is an
DEFINING UST
It’s a somewhat hazy area, but it’s generally agreed that, to qualify for the description ‘ultra-short’, a lens should have a throw ratio of 0.38 or less – in other words, to deliver a 60in wide image, the projector lens can be placed 22.8in from the screen. ‘Short throw’ is generally defi ned as representing a throw ratio of between 0.38 and 0.75, while the typical projector has a throw ratio of between 1.5 and 3.5.
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