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The ED80 is a doublet with an ED ( extra dense flint glass element), there are no additional lens assemblies on the inside.
You may have been seeing the edge of the internal baffle?
I have a "high end" televue 4" f5 Genesis refractor and that design has a secondary lens assembly just infront of the focusser to give a better colour corrected flat field. ( But costs about ten times as much as the ED80!)
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