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Shine a green laser through the objective. If you can see the laser in the lens its not fluorite. Flourite lenses have low dispersion so a triplet of lesser glasses but one element of fluorite will show up the laser in the non-fluorite lenses but nothing in the fluorite element.
I have done this myself with a TEC 180 fluorite triplet. You can clearly see the beam in the 2 non fluorite elements and it disappears in the fluorite element.
Its enough to make you want to only use fluorite scopes.
You'll notice that in an astrophoto using a fluorite scope. There will be some faint wisps of nebula that it picks up that other lenses do not as well.
Greg.
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