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Back in the 70's I changed from a 6" f8 to a 12" f5 telescope and found my old ramsden eyepieces could not cope with the fast f5, I changed to UO orthos and they worked reasonably well. As my eye become more "trained" over the years I found the distortions to be more and more objectionable and ended up selling them to go to TV Plossls. The orthos only have three glass elements, and although the quality of glass has improved, my opinion is that the basic design is still limited to shorter EP focal lengths and slow systems ie > f8.
There's not much to beat a good plossl or Nagler, especially on fast systems < f5.
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