Quote:
Originally Posted by Hans Tucker
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
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Those numbers would suggest a major difference between the common glasses used in telescopes, FPL-51 and FPL-53. But, how does that translate at the eyepiece or at the CCD chip? IS the color correction 15-20% better or does it scale differently?