Quote:
Originally Posted by Astronovice
Thank you Greg,
Your comments are most helpful.
Am I right in assuming that Hoya FCD100 and Ohara FPL53 are broadly equivalent?
Calvin
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It depends on how broadly you want to define equivalent.
FPL-53 offers almost indistinguishable performance compared to Fluorite/CaF2, in an astronomical refractor, it’s more stable, has better physical characteristics, cost far less, and it's environmentally better to work with. FPL-53 has an Abbe number of 94.99 .
FCD-100. The relatively new Extra Low Dispersion Hoya FCD-100 glass has an Abbe number of 94.66 compared to 94.99 of S-FPL53.
To most, if not all eyes using it visually, Flourite, FPL-53, and FCD-100, will appear to be the same. FCD-100 is more cost effective currently, but many astronomers buy on reputation, even if they cannot visually tell the difference, and Flourite and FPL-53 continue to sit at the top in people minds.