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6 July 2006 Large optical glass lenses for ELTs
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ELTs will need large optical lenses for imaging optics and atmospheric dispersion correctors. The extreme dimensions of lenses considered in designs at present (up to 1.7 m diameter) pose severe challenges for the specification, production and inspection of the glass blanks. Possible maximum sizes, their very long production time, technical and economical conditions and probable restrictions are discussed. The inspection of glass blanks for ELT transmission optics can rely on methods already introduced for optical glass blanks of conventional sizes and for large mirror blanks of the glass-ceramic ZERODUR(r) for most of their properties. However, especially for the refractive index homogeneity a scale-up still has to be achieved. At present largest homogeneity interferometers have apertures about 500 to 600 mm. The development of larger ones is very time consuming, about 2 - 3 years. There is a need for a close agreement on the required capability of the measurement method between the optical designers and the supplier and to start soon with this since the optical lenses may turn out to be more critical in production than the segments for the primary mirrors.
© (2006) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Peter Hartmann and Ralf Jedamzik "Large optical glass lenses for ELTs", Proc. SPIE 6273, Optomechanical Technologies for Astronomy, 62730H (6 July 2006);


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