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Message: <blockquote data-quote="denco@comcast.n" data-source="post: 3665713" data-attributes="member: 25300">Why does Zeiss make such a big deal about their HT Schott glass used in the HT then? The HT has 95% transmission with the HT Schott glass but the SF has 93% transmission with normal HD glass. Glass types and grades must make a difference in transmission."SCHOTT has recently developed this HT optical glass that has significantly improved transmittance levels and which is especially suitable for digital projection and high end optical systems. They currently market eleven of these special versions that are labeled HT or HTultra and are said to be working hard to expand its offerings on an ongoing basis."<a href="https://www.bestbinocularsreviews.com/blog/ht-glass-from-schott-06/" target="_blank">https://www.bestbinocularsreviews.com/blog/ht-glass-from-schott-06/</a><a href="http://www.schott.com/advanced_optics/english/products/optical-materials/optical-glass/ht-and-htultra/index.html" target="_blank">http://www.schott.com/advanced_optics/english/products/optical-materials/optical-glass/ht-and-htultra/index.html</a></blockquote>