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I was going to ask if this was genuine fluorite as some manufacturers (notably William Optics) call FPL53 fluorite. FPL53 has a lot of fluorite in it but its deliberately misleading. Fluorite lenses have less scatter and enable the optics designer to achieve a faster F ratio with better colour correction as with TEC fluorite scopes. If you look at the strehl for different wavelengths the fluorite models seem to do better. Fluorite has less light scatter as well if you do the green laser test where its invisible when it goes through the fluorite element but you can see it in the other lesser glass elements.
So if there is any doubt shine a green laser through it and see if you can see the beam. If you can its not fluorite.
Greg.
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