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  1. J

    New user and "new" Kowa TSN3

    Hi, first of all, welcome to BF! What do you mean by the sentence above? Do you really have the rather rare later variant with multicoatings and a protective glass in fromt of the prism assembly? In that case, you will be indeed limited to old or current Kowa small body EPs - the 30x wide is...
  2. J

    New user and "new" Kowa TSN3

    Hi Luca, yes, as I wrote, the old 20-60 zoom from the 90s is not great... and usually lateral CA is caused mainly by the EP, but of course the focal ratio does play a role - and the TSN-3 is quite a bit faster than the 613... and the steeper light cone makes things more difficult for the EP...
  3. J

    New user and "new" Kowa TSN3

    Hi, first of all, welcome to birdforum! A good example of TSN-3 should offer a crisp image at 60x too - with a proper EP and in good seeing. The old Kowa 20-60x zoom with the rubber eyecup is usually not great. Regarding chromatic aberration or CA, there are two kinds - one is called axial or...
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