Quote:
Originally Posted by AG Hybrid
Well how 'bout that? "The finest performance requires the finest materials such as high index lanthanum and fluorite type glasses, in some cases costing up to 15x more than ordinary glass types."
I suppose FPL designated glass would be considered Fluorite type glass.
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Not quite all FPL, only FPL-53 (artifical fluorite) has been regarded as being close to calcium fluorite type glass because its abbe value (94.93) is close to that of genuine fluorite (94.99). FPL-51 has an abbe number of 81.54 and FPL-52 has an abbe number of 90.29.
Apparently FPL stands for:
F - Fluorite
P - Lead
L - Low refractive index
51, 52 or 53 - The 51st, 52nd or 53rd glass in its family