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To the original poster. Yes I think you have that right.
The reason why reflecting telescopes are considered APO (well the term isn't really applied to them) is because a mirror reflects without splitting white light into its colours unlike an objective lens.
Hence FPL53 etc which splits the light into its various colours far less than regular glasses.
3 elements in an objective is inapplicable for a definition. Roland Christen has made the comment that he could make an APO doublet. Tak FS series were close to APO but had some false colour.
Greg.
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