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  1. E

    115 objective focal length and f-number

    Thank you for pointing out that we are not looking at simple refractors any more, even though optics remain stuck with measurements from that era. You are of course spot on, scopes are not simple designs, so that even basic measurements are hard to find. Swaro seems on course to keep its secrets.
  2. E

    115 objective focal length and f-number

    Is there not some convention for this, such as center of the first glass surface to center of the focused image?
  3. E

    115 objective focal length and f-number

    So now I'm confused. Is the focal length 1% more than 551 mm, as measured by Henri Link above, or 431 mm as measured by the OP?
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