Quote:
Originally Posted by g__day
A slight aside - given the common claim of apo grade optics - on ED refractors - its interest to see Takahashi coin the term ortho apochoramatic for their line - meaning true colour correctness - even if slightly out of focus either way - that's impressive!
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I think Takahashi's use of ortho apochromatic has more to do with differentiating it from a regular triplet apochromat through it's use of two fluoro-glass elements, compared to the common triplet apo's use of one fluoro-glass or fluorite element.
With regard to the Apo claim on ED Apo refractors - most of them will meet the requirements of visual astronomers. It is not until you start using them photographically that you will really start to notice a big difference as you need colour correction across a far broader spectrum.