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Message: <blockquote data-quote="maico" data-source="post: 3665826" data-attributes="member: 139687">I used to have a mark.1 Canon 300 f2.8 S.S.C (1974-78), which was black and used to rack out for focusing. One of the front elements was a large fluorite crystal not a fluorite glass melt. The control of chromatic aberrations was noticeably better than the slower 300mm f4 or f4.5 lenses of that time and the lens shorter. These large crystals had a reputation of fracturing where the ring held the element down and for hazing over. Later Canon super telephoto lenses solved these use problems.I sold it for spares or repair for a pittance but regret now not retrieving the crystal as a paperweight and curio !<a href="http://www.mir.com.my/rb/photography/companies/canon/fdresources/fdlenses/fluorite300mmSSC/300mmFlouriteSteven9.jpg" target="_blank">http://www.mir.com.my/rb/photography/companies/canon/fdresources/fdlenses/fluorite300mmSSC/300mmFlouriteSteven9.jpg</a><a href="http://www.mir.com.my/rb/photography/companies/canon/fdresources/fdlenses/fluorite300mmSSC/300mmFlouriteSteven6.jpg" target="_blank">http://www.mir.com.my/rb/photography/companies/canon/fdresources/fdlenses/fluorite300mmSSC/300mmFlouriteSteven6.jpg</a>Schott are the largest growers of synthetic calcium fluorite crystal and apparently have 80% of the World market these days.</blockquote>