We have developed a new optical system for projection television to achieve high luminance and excellent image quality with light weight compact size cabinet. This optical lens system has a hybrid structure employing four plastic and one glass lens. By introducing an aspherical surface on both sides of all plastic lenses, we have achieved an improvement of image quality over the entire screen. The lenses controlled to be thinner in this design method simplifies molding. Plastic lenses are imperfect in that they are subject to focus drift due to changes in ambient temperature. To minimize this effect, glass is employed in the main power lens. Furthermore, the lenses are arranged in such a way to eliminate the drift by optimum use of power distribution. This system has a short focal length and thus employs a single-reflection optical path system, ensuring a compact cabinet size and a reduction of chromatic abberation which cannot be achieved by simply introducing aspherical lenses. The design reduced the focal length from our conventional figure of 156 mm to 86 mm. Despite the large aperture FN0 of 1.0 an approximate increase of 30% in the MTF value has been achieved. The image quality is perfectly maintained over a temperature fluctuations of ± 20°C. Overall weight of the lens assembly has been reduced by 1/5. The system has been in operation in Pioneer 40 and 50 inch T.V. sets since 1987. The system is applicable to and essential for the future HDTV.

Date Published: 11 July 1989
PDF: 7 pages
Proc. SPIE 1081, Projection Display Technology, Systems, and Applications, (11 July 1989); doi: 10.1117/12.952842

Published in SPIE Proceedings Vol. 1081:
Projection Display Technology, Systems, and Applications
Frederic J. Kahn, Editor(s)