Quote:
Originally Posted by rmuhlack
isn't an apo optical system meant to bring visible light to focus at a common focal point?
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An achromat brings two wavelengths to focus at the same point. An apochromat brings three wavelengths to focus at the same point. The laws of Physics prevent a refractor from being perfect, alas, but you can get closer at long f/ratios. At short f/ratios even an apo has noticeable shortcomings. We do out best to fix those in PixInsight
Cheers,
Rick.