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Message: <blockquote data-quote="kabsetz" data-source="post: 3665665" data-attributes="member: 10167">Dennis,Dennis says (post#35):"Fluorite crystal glass is one of the highest performing glasses used in optics with very high transmission and CA control. It is also lighter than standard glass another advantage. Canon uses it in their L-series lenses meaning the Canon 10x42 IS-L binoculars has it."Canon says: "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."Close, but not the same thing. In order not to mislead readers, it is better not make exaggerated claims or draw false conclusions.As far as the light transmission question: if calcium fluorite elements are used in a birding binocular or a telescope, thus far there has been one lens element made of it in the optical train. The thickness of said element is about one tenth or less compared to the length of the light path in the erecting prisms. The contribution to the total light loss of changing that one lens from fluoro crown glass or similar to true calcium fluorite is practically zero. The value of CaF2 comes from reduced CA, and this improvement is very real and desirable.Kimmo</blockquote>