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A lot of theory. I would want to simply evaluate images taken with the scopes/ The images tell you if the lens is OK or not.
I have used several fluorite scopes and they are a slight cut above FPL53 scopes. Usually better colour in the images and a little bit brighter image.
Fluorite allows the optical designer the freedom to achieve a faster F ratio without sacrificing optical performance. It also has less light scatter.
But a fluorite doublet - is it really an APO? Tak calls them APOs but I my old FS152 was superb as a visual instrument but you did get the odd blue ringed bright star with it imaging.
These ED glass/Lanthanum element lenses look interesting. I have not heard of one in a triplet yet only doublets. Which scopes have them in a triplet?
Greg.
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