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18 December 2012 110 years BK7: optical glass type with long tradition and ongoing progress
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The SCHOTT glass catalog of 1906 lists the borosilicate crown glass type BK7 for the first time. Since that time it has grown to a high volume glass with equivalents available from all glass manufacturers and became so omnipresent, that many people value it as a cheap bulk commodity type not worthwhile to be looked at closer. This might hold for small thin lenses. However, BK7 can be produced from strip glass format over thick blocks up to large disks of more than 1 m diameter and half a meter thickness. Achieving high homogeneity in thicknesses of 50 mm and above is far from trivial and with increasing thickness it is a challenge even for outstanding glass producers. The present state-of-the-art at SCHOTT is represented by a world record refractive index homogeneity of 1•10-6 peak-to-valley in block glass with more than 200 x 200 mm2 and 100 mm thickness measured in all directions top-to-bottom and in lateral directions. The progress in transmittance led to the introduction of a new quality grade N-BK7HT. The transmittance improvement in the blue-violet spectral range leads to noticeably better twilight vision in use with binocular prisms and image stability in cinema digital projection.
© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Peter Hartmann "110 years BK7: optical glass type with long tradition and ongoing progress", Proc. SPIE 8550, Optical Systems Design 2012, 85500U (18 December 2012);

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