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Fluorite
It will be a fluoro crown glass Barry used, not a CaF2 crystal (real Calciumfluorit).
But nowerdays many lenses with fluoro crown glass like Ohara FLP-53 are called fluorite, this is marketing.
Fluoro crown glass in doublets cannot match Calciumfluorites in doublets due to the superior optical properties of Calciumfluorite.
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