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Message: <blockquote data-quote="denco@comcast.n" data-source="post: 3665630" data-attributes="member: 25300">There are a lot of astronomers over at Cloudy Night's that  disagree with you. They could be wrong but they are pretty knowledgeable when it comes to optical glass. I challenge you to find some facts that says Fluorite Crystal does not have higher transmission than other glasses used in optics. From Cloudy Night's."The use of CalciumFluorite crystal in optics is based on the fact that caracteristics like refractive index (<1.435), low disperiosn (~95.24) and light transmission of this material are at extreme ends which cannot be achived with commercial available modern abnormal index glass compositions.Whilst fluoro crown glass like FK 54 (Schott), FCD 10 (Hoya) oder FPL 53 (Ohara) has properties which are closer to Calciumfluorite, it is still falling short.To call lenses made of fluoro crown glass fluorite lenses is misleading and is a marketing attempt to sell on the back of the outstanding performance/ reputation of telescopes which used Calciumfluorit elements such as the Takahashi FS-102, FS-128, FS-150, the Vixen 102 and Calciumfluorit doublets of current production.Doublets with one Calciumfluorite lens and a glass will still (if properly deisgned) outperform glass doublets based on the best commercial available glas compositions. Calciumfluoride is still widely used in photographic, microscopic, lithograpy and other high performance optics, including latest HD TV camera lenses as well as in some current telescope designs. Latest might be the new 90/500 Borg which is said to have a CaF2 lens in the doublet (a new Sky90 type of scope?). To my knowledge the biggest pieces of commercially available Calciumfluorite manufactured right now are about 400mm diameter.There are quite a number of suppliers worldwide, amongst others the Canon subsidiary Canon Optron in Japan, Hellma in Germany and SCHOTT LITHOTEC in Jena/ Germany.It must be said that on laboratory scale companys like Schott, Hoya, Ohara and Corning have glass based compositions which approach Calciumfluorite caracteristics, but these are not available on the market today due to prohibitive cost.bratislav"Canon says this about their UD lenses used in the Canon 10x42 IS-L. So they are not specifically fluorite crystal but close in performance."UD glass is similar to fluorite in that it features a low refractive index and low dispersion. Although it is not quite as good as fluorite, its performance is significantly better than ordinary optical glass. So by using UD glass Canon has been able to manufacture a range of lenses with superior performance and at a lower cost than before."<a href="http://cpn.canon-europe.com/content/education/infobank/lenses/fluorite_aspherical_and_ud_lenses.do" target="_blank">http://cpn.canon-europe.com/content/education/infobank/lenses/fluorite_aspherical_and_ud_lenses.do</a></blockquote>

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