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This is a KzFSN2 and FPL 53 doublet (one of Skywatcher ED120/900 variants after a redesign).
3 color crossings. Two lenses.
And plenty of those measured by Wolfgang Rohr, confirming the performance in his lab.
BTW, we'd have very similar curve ("S" curve, denoting three crossings) if we paired KzFSN2 with FPL51, FPL52, FCD-1, FCD100 or FPL55. We can also use some Lantanum glass to have same effect. And don't get me started on Fluorite.
Plenty of doublets with 3 crossings.
Last edited by bratislav; 15-03-2019 at 09:32 PM.
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