Hi again,
I just re-read the thread and then the relevant paragraph from Don's expertise:
"2. Chromatic Aberration-lateral and fringe. Yes, eyepieces, like achromatic lenses, can produce chromatic aberration in a given scope. What's seen may be from the objective, if a refractor, but eyepieces are not immune to this. On axis chromatic aberration is rare, so that would probably be from the objective. But lateral chromatic aberration can be simply having an oblique angle interact poorly with the coatings used (because their spectra of transmission varies with angle) or because of glass angle interactions. It is very hard to produce an ultrawide field in an eyepiece and NOT have any chromatic dispersion at the edge. Edge chromaticism can be a result of holding the eye at the wrong angle, too, since our eyes are not immune to chomatic effects. If it's seen at the edge, try holding the eye differently to see if it disappears. If it does, it was in the eye. if it doesn't, it's in the eyepiece. Good suppression of this leads to high-priced eyepieces, so a less-costly cure may be to restrict the field of view.
Many eyepieces have a tiny ring of aberrant color at the edge of the field. This is usually due to the oblique angle of vision at the edge of the lens and the coatings selected for the anti-reflection coatings on the lens."
No surprise that CA would be the diagnosis . . .
Best,
Ed
P.S. Sometimes I post for a wider audience than just the OP . . . to benefit others who also read the thread later . . .